1.
Radar
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Radar is an object-detection system that uses radio waves to determine the range, angle, or velocity of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, Radio waves from the transmitter reflect off the object and return to the receiver, giving information about the objects location and speed. Radar was developed secretly for military use by several nations in the period before, the term RADAR was coined in 1940 by the United States Navy as an acronym for RAdio Detection And Ranging or RAdio Direction And Ranging. The term radar has since entered English and other languages as a common noun, high tech radar systems are associated with digital signal processing, machine learning and are capable of extracting useful information from very high noise levels. Other systems similar to make use of other parts of the electromagnetic spectrum. One example is lidar, which uses ultraviolet, visible, or near infrared light from lasers rather than radio waves, as early as 1886, German physicist Heinrich Hertz showed that radio waves could be reflected from solid objects. In 1895, Alexander Popov, an instructor at the Imperial Russian Navy school in Kronstadt. The next year, he added a spark-gap transmitter, in 1897, while testing this equipment for communicating between two ships in the Baltic Sea, he took note of an interference beat caused by the passage of a third vessel. In his report, Popov wrote that this phenomenon might be used for detecting objects, the German inventor Christian Hülsmeyer was the first to use radio waves to detect the presence of distant metallic objects. In 1904, he demonstrated the feasibility of detecting a ship in dense fog and he obtained a patent for his detection device in April 1904 and later a patent for a related amendment for estimating the distance to the ship. He also got a British patent on September 23,1904 for a radar system. It operated on a 50 cm wavelength and the radar signal was created via a spark-gap. In 1915, Robert Watson-Watt used radio technology to advance warning to airmen. Watson-Watt became an expert on the use of direction finding as part of his lightning experiments. As part of ongoing experiments, he asked the new boy, Arnold Frederic Wilkins, Wilkins made an extensive study of available units before selecting a receiver model from the General Post Office. Its instruction manual noted that there was fading when aircraft flew by, in 1922, A. Hoyt Taylor and Leo C. Taylor submitted a report, suggesting that this might be used to detect the presence of ships in low visibility, eight years later, Lawrence A. Australia, Canada, New Zealand, and South Africa followed prewar Great Britain, and Hungary had similar developments during the war. Hugon, began developing a radio apparatus, a part of which was installed on the liner Normandie in 1935
2.
Doppler effect
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The Doppler effect is the change in frequency or wavelength of a wave for an observer moving relative to its source. It is named after the Austrian physicist Christian Doppler, who proposed it in 1842 in Prague, a common example of Doppler shift is the change of pitch heard when a vehicle sounding a siren or horn approaches, passes, and recedes from an observer. Compared to the frequency, the received frequency is higher during the approach, identical at the instant of passing by. When the source of the waves is moving towards the observer, therefore, each wave takes slightly less time to reach the observer than the previous wave. Hence, the time between the arrival of successive wave crests at the observer is reduced, causing an increase in the frequency, while they are travelling, the distance between successive wave fronts is reduced, so the waves bunch together. The distance between wave fronts is then increased, so the waves spread out. For waves that propagate in a medium, such as sound waves, the total Doppler effect may therefore result from motion of the source, motion of the observer, or motion of the medium. Each of these effects is analyzed separately, for waves which do not require a medium, such as light or gravity in general relativity, only the relative difference in velocity between the observer and the source needs to be considered. Doppler first proposed this effect in 1842 in his treatise Über das farbige Licht der Doppelsterne und einiger anderer Gestirne des Himmels, the hypothesis was tested for sound waves by Buys Ballot in 1845. He confirmed that the pitch was higher than the emitted frequency when the sound source approached him. Hippolyte Fizeau discovered independently the same phenomenon on electromagnetic waves in 1848, in Britain, John Scott Russell made an experimental study of the Doppler effect. The frequency is decreased if either is moving away from the other, the above formula assumes that the source is either directly approaching or receding from the observer. If the source approaches the observer at an angle, the frequency that is first heard is higher than the objects emitted frequency. When the observer is close to the path of the object. When the observer is far from the path of the object, to understand what happens, consider the following analogy. Someone throws one ball every second at a man, assume that balls travel with constant velocity. If the thrower is stationary, the man will receive one every second. However, if the thrower is moving towards the man, he will receive balls more frequently because the balls will be spaced out
3.
Microwave
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Microwaves are a form of electromagnetic radiation with wavelengths ranging from one meter to one millimeter, with frequencies between 300 MHz and 300 GHz. Different sources define different frequency ranges as microwaves, the broad definition includes both UHF and EHF bands. A more common definition in radio engineering is the range between 1 and 100 GHz, in all cases, microwaves include the entire SHF band at minimum. Frequencies in the range are often referred to by their IEEE radar band designations, S, C, X, Ku, K, or Ka band. The prefix micro- in microwave is not meant to suggest a wavelength in the micrometer range and it indicates that microwaves are small, compared to waves used in typical radio broadcasting, in that they have shorter wavelengths. The boundaries between far infrared, terahertz radiation, microwaves, and ultra-high-frequency radio waves are fairly arbitrary and are used variously between different fields of study. At the high end of the band they are absorbed by gases in the atmosphere, microwaves are extremely widely used in modern technology. Although at the low end of the band they can pass through building walls enough for useful reception, therefore on the surface of the Earth microwave communication links are limited by the visual horizon to about 30 -40 miles. Microwaves are absorbed by moisture in the atmosphere, and the attenuation increases with frequency, beginning at about 40 GHz, atmospheric gases also begin to absorb microwaves, so above this frequency microwave transmission is limited to a few kilometers. A spectral band structure causes absorption peaks at specific frequencies, in a microwave beam directed at an angle into the sky, a small amount of the power will be randomly scattered as the beam passes through the troposphere. A sensitive receiver beyond the horizon with a high gain antenna focused on that area of the troposphere can pick up the signal. This technique has been used at frequencies between 0.45 and 5 GHz in tropospheric scatter communication systems to communicate beyond the horizon and their short wavelength allows narrow beams of microwaves to be produced by conveniently small high gain antennas from a half meter to 5 meters in diameter. Therefore beams of microwaves are used for point-to-point communication links, an advantage of narrow beams is that they allow frequency reuse by nearby transmitters. Parabolic antennas are the most widely used directive antennas at microwave frequencies, flat microstrip antennas are being increasingly used in consumer devices. Where omnidirectional antennas are required, for example in wireless devices and Wifi routers for wireless LANs, small monopoles, dipole, or patch antennas are used. Due to the high cost and maintenance requirements of waveguide runs, the term microwave also has a more technical meaning in electromagnetics and circuit theory. As a consequence, practical microwave circuits tend to away from the discrete resistors, capacitors. Open-wire and coaxial transmission lines used at lower frequencies are replaced by waveguides and stripline, high-power microwave sources use specialized vacuum tubes to generate microwaves
4.
Aviation
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Aviation is the practical aspect or art of aeronautics, being the design, development, production, operation and use of aircraft, especially heavier than air aircraft. The word aviation was coined by French writer and former naval officer Gabriel La Landelle in 1863, from the verb avier, itself derived from the Latin word avis and the suffix -ation. The modern age of aviation began with the first untethered human lighter-than-air flight on November 21,1783, the practicality of balloons was limited because they could only travel downwind. It was immediately recognized that a steerable, or dirigible, balloon was required, jean-Pierre Blanchard flew the first human-powered dirigible in 1784 and crossed the English Channel in one in 1785. Rigid airships became the first aircraft to transport passengers and cargo over great distances, the best known aircraft of this type were manufactured by the German Zeppelin company. The most successful Zeppelin was the Graf Zeppelin and it flew over one million miles, including an around-the-world flight in August 1929. However, the dominance of the Zeppelins over the airplanes of that period, the Golden Age of the airships ended on May 6,1937 when the Hindenburg caught fire, killing 36 people. The cause of the Hindenburg accident was blamed on the use of hydrogen instead of helium as the lift gas. An internal investigation by the manufacturer revealed the coating used to protect the material over the frame was highly flammable. Changes to the coating formulation reduced the risk of further Hindenburg type accidents, although there have been periodic initiatives to revive their use, airships have seen only niche application since that time. In 1799 Sir George Cayley set forth the concept of the airplane as a fixed-wing flying machine with separate systems for lift, propulsion. Seven years later, on 14 October 1897, Aders Avion III was tested without success in front of two officials from the French War ministry, the report on the trials was not publicized until 1910, as they had been a military secret. In November 1906 Ader claimed to have made a flight on 14 October 1897. Although widely believed at the time, these claims were later discredited, however, the most widely accepted date is December 17,1903 by the Wright brothers. The Wright brothers were the first to fly in a powered and controlled aircraft, previous flights were gliders or free flight, but the Wright brothers combined both, setting the new standard in aviation records. Aircraft began to transport people and cargo as designs grew larger, the Wright brothers took aloft the first passenger, Charles Furnas, one of their mechanics, on May 14,1908. By the beginning of World War II, many towns and cities had built airports, the war brought many innovations to aviation, including the first jet aircraft and the first liquid-fueled rockets. Manufacturers such as Cessna, Piper, and Beechcraft expanded production to provide aircraft for the new middle-class market
5.
Major League Baseball
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Major League Baseball is a professional baseball organization, the oldest of the four major professional sports leagues in the United States and Canada. A total of 30 teams now play in the National League and American League, the NL and AL operated as separate legal entities from 1876 and 1901 respectively. After cooperating but remaining legally separate entities since 1903, the merged into a single organization led by the Commissioner of Baseball in 2000. The organization also oversees Minor League Baseball, which comprises about 240 teams affiliated with the Major League clubs, with the World Baseball Softball Confederation, MLB manages the international World Baseball Classic tournament. Baseballs first professional team was founded in Cincinnati in 1869,30 years after Abner Doubleday supposedly invented the game of baseball, the first few decades of professional baseball were characterized by rivalries between leagues and by players who often jumped from one team or league to another. The period before 1920 in baseball was known as the dead-ball era, Baseball survived a conspiracy to fix the 1919 World Series, which came to be known as the Black Sox Scandal. The sport rose in popularity in the 1920s, and survived potential downturns during the Great Depression, shortly after the war, baseballs color barrier was broken by Jackie Robinson. The 1950s and 1960s were a time of expansion for the AL and NL, then new stadiums, Home runs dominated the game during the 1990s, and media reports began to discuss the use of anabolic steroids among Major League players in the mid-2000s. In 2006, an investigation produced the Mitchell Report, which implicated many players in the use of performance-enhancing substances, today, MLB is composed of thirty teams, twenty-nine in the United States and one in Canada. Baseball broadcasts are aired on television, radio, and the Internet throughout North America, MLB has the highest season attendance of any sports league in the world with more than 73 million spectators in 2015. MLB is governed by the Major League Baseball Constitution and this document has undergone several incarnations since 1875, with the most recent revisions being made in 2012. Under the direction of the Commissioner of Baseball, MLB hires and maintains the sports umpiring crews, and negotiates marketing, labor, MLB maintains a unique, controlling relationship over the sport, including most aspects of Minor League Baseball. This ruling has been weakened only slightly in subsequent years, the weakened ruling granted more stability to the owners of teams and has resulted in values increasing at double-digit rates. There were several challenges to MLBs primacy in the sport between the 1870s and the Federal League in 1916, the last attempt at a new league was the aborted Continental League in 1960. The chief executive of MLB is the commissioner, Rob Manfred, the chief operating officer is Tony Petitti. There are five other executives, president, chief officer, chief legal officer, chief financial officer. The multimedia branch of MLB, which is based in Manhattan, is MLB Advanced Media and this branch oversees MLB. com and each of the 30 teams websites. Its charter states that MLB Advanced Media holds editorial independence from the league, MLB Productions is a similarly structured wing of the league, focusing on video and traditional broadcast media
6.
Meteorology
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Meteorology is a branch of the atmospheric sciences which includes atmospheric chemistry and atmospheric physics, with a major focus on weather forecasting. The study of meteorology dates back millennia, though significant progress in meteorology did not occur until the 18th century, the 19th century saw modest progress in the field after weather observation networks were formed across broad regions. Prior attempts at prediction of weather depended on historical data, Meteorological phenomena are observable weather events that are explained by the science of meteorology. Different spatial scales are used to describe and predict weather on local, regional, Meteorology, climatology, atmospheric physics, and atmospheric chemistry are sub-disciplines of the atmospheric sciences. Meteorology and hydrology compose the interdisciplinary field of hydrometeorology, the interactions between Earths atmosphere and its oceans are part of a coupled ocean-atmosphere system. Meteorology has application in diverse fields such as the military, energy production, transport, agriculture. The word meteorology is from Greek μετέωρος metéōros lofty, high and -λογία -logia -logy, varāhamihiras classical work Brihatsamhita, written about 500 AD, provides clear evidence that a deep knowledge of atmospheric processes existed even in those times. In 350 BC, Aristotle wrote Meteorology, Aristotle is considered the founder of meteorology. One of the most impressive achievements described in the Meteorology is the description of what is now known as the hydrologic cycle and they are all called swooping bolts because they swoop down upon the Earth. Lightning is sometimes smoky, and is then called smoldering lightning, sometimes it darts quickly along, at other times, it travels in crooked lines, and is called forked lightning. When it swoops down upon some object it is called swooping lightning, the Greek scientist Theophrastus compiled a book on weather forecasting, called the Book of Signs. The work of Theophrastus remained a dominant influence in the study of weather, in 25 AD, Pomponius Mela, a geographer for the Roman Empire, formalized the climatic zone system. According to Toufic Fahd, around the 9th century, Al-Dinawari wrote the Kitab al-Nabat, ptolemy wrote on the atmospheric refraction of light in the context of astronomical observations. St. Roger Bacon was the first to calculate the size of the rainbow. He stated that a rainbow summit can not appear higher than 42 degrees above the horizon, in the late 13th century and early 14th century, Kamāl al-Dīn al-Fārisī and Theodoric of Freiberg were the first to give the correct explanations for the primary rainbow phenomenon. Theoderic went further and also explained the secondary rainbow, in 1716, Edmund Halley suggested that aurorae are caused by magnetic effluvia moving along the Earths magnetic field lines. In 1441, King Sejongs son, Prince Munjong, invented the first standardized rain gauge and these were sent throughout the Joseon Dynasty of Korea as an official tool to assess land taxes based upon a farmers potential harvest. In 1450, Leone Battista Alberti developed a swinging-plate anemometer, and was known as the first anemometer, in 1607, Galileo Galilei constructed a thermoscope
7.
Radar gun
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A radar speed gun is a device used to measure the speed of moving objects. A radar speed gun is a Doppler radar unit that may be hand-held, vehicle-mounted or static. The radar speed gun was invented by John L. Barker Sr. and Ben Midlock, originally, Automatic Signal was approached by Grumman Aircraft Corporation to solve the specific problem of terrestrial landing gear damage on the now-legendary PBY Catalina amphibious aircraft. Barker and Midlock cobbled a Doppler radar unit from coffee cans soldered shut to make microwave resonators, the unit was installed at the end of the runway, and aimed directly upward to measure the sink rate of landing PBYs. After the war, Barker and Midlock tested radar on the Merritt Parkway, in 1947, the system was tested by the Connecticut State Police in Glastonbury, Connecticut, initially for traffic surveys and issuing warnings to drivers for excessive speed. Starting in February 1949, the police began to issue speeding tickets based on the speed recorded by the radar device. In 1948, radar was used in Garden City, New York. Speed guns use Doppler radar to perform speed measurements, Radar speed guns, like other types of radar, consist of a radio transmitter and receiver. They send out a signal in a narrow beam, then receive the same signal back after it bounces off the target object. From that difference, the radar speed gun can calculate the speed of the object from which the waves have been bounced. After the returning waves are received, a signal with a equal to this difference is created by mixing the received radio signal with a little of the transmitted signal. Since this type of speed gun measures the difference in speed between a target and the gun itself, the gun must be stationary in order to give a correct reading. Instead of comparing the frequency of the signal reflected from the target with the transmitted signal, the frequency difference between these two signals gives the true speed of the target vehicle. Modern radar speed guns normally operate at X, K, Ka, Radar guns that operate using the X band frequency range are becoming less common because they produce a strong and easily detectable beam. Also, most automatic doors utilize radio waves in the X band range, as a result, K band and Ka band are most commonly used by police agencies. For these reasons, hand-held radar typically includes an on-off trigger, Radar detectors are illegal in some areas. Traffic radar comes in many models, hand-held units are mostly battery powered, and for the most part are used as stationary speed enforcement tools. Stationary radar can be mounted in vehicles and may have one or two antennae
8.
Radiology
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Radiology is a specialty that uses medical imaging to diagnose and treat diseases seen within the body. Interventional radiology is the performance of medical procedures with the guidance of imaging technologies, the acquisition of medical images is usually carried out by the Radiographer, often known as a Radiologic Technologist. Depending on location, the Diagnostic Radiologist, or Reporting Radiographer, then interprets or reads the images and produces a report of their findings and this report is then transmitted to the Clinician who requested the imaging, either routinely or emergently. Radiographs are produced by transmitting X-rays through a patient, the X-rays are projected through the body onto a detector, an image is formed based on which rays pass through versus those that are absorbed or scattered in the patient. Röntgen discovered X-rays on November 8,1895 and received the first Nobel Prize in Physics for their discovery in 1901, in film-screen radiography, an X-ray tube generates a beam of X-rays, which is aimed at the patient. The film is then developed chemically and an image appears on the film, film-screen radiography is being replaced by computed radiography but more recently by digital radiography and the EOS imaging. In the two latest systems, the X-rays strike sensors that converts the signals generated into digital information, in digital radiography the sensors shape a plate, but in the EOS system, which is a slot-scanning system, a linear sensor vertically scans the patient. Plain radiography was the imaging modality available during the first 50 years of radiology. Due to its availability, speed, and lower costs compared to other modalities, also despite the large amount of data in CT scans, MR scans and other digital-based imaging, there are many disease entities in which the classic diagnosis is obtained by plain radiographs. Examples include various types of arthritis and pneumonia, bone tumors, fractures, congenital skeletal anomalies, mammography and DXA are two applications of low energy projectional radiography, used for the evaluation for breast cancer and osteoporosis, respectively. Fluoroscopy and angiography are special applications of X-ray imaging, in which a fluorescent screen and this allows real-time imaging of structures in motion or augmented with a radiocontrast agent. Two radiocontrast agents are presently in common use, barium sulfate is given orally or rectally for evaluation of the GI tract. Iodine, in multiple forms, is given by oral, rectal, intra-arterial or intravenous routes. Iodine contrast may also be concentrated in areas more or less than in normal tissues. CT imaging uses X-rays in conjunction with computing algorithms to image the body, in CT, an X-ray tube opposite an X-ray detector in a ring-shaped apparatus rotate around a patient, producing a computer-generated cross-sectional image. CT is acquired in the plane, with coronal and sagittal images produced by computer reconstruction. Radiocontrast agents are used with CT for enhanced delineation of anatomy. Although radiographs provide higher resolution, CT can detect more subtle variations in attenuation of X-rays
9.
Health care
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It includes the work done in providing primary care, secondary care, and tertiary care, as well as in public health. Access to healthcare varies across countries, groups, and individuals, largely influenced by social, countries and jurisdictions have different policies and plans in relation to the personal and population-based health care goals within their societies. Healthcare systems are organizations established to meet the needs of target populations. Their exact configuration varies between national and subnational entities, in some countries and jurisdictions, healthcare planning is distributed among market participants, whereas in others, planning occurs more centrally among governments or other coordinating bodies. Healthcare can contribute to a significant part of a countrys economy. In 2011, the healthcare industry consumed an average of 9.3 percent of the GDP or US$3,322 per capita across the 34 members of OECD countries.1 years, a gain of 10 years since 1970. The USA ranges only on place 26 among the 34 OECD member countries, all OECD countries have achieved universal health coverage, except Mexico and the USA. Healthcare is conventionally regarded as an important determinant in promoting the general physical and mental health, an example of this was the worldwide eradication of smallpox in 1980, declared by the WHO as the first disease in human history to be completely eliminated by deliberate health care interventions. The delivery of health care depends on groups of trained professionals and paraprofessionals coming together as interdisciplinary teams. Healthcare can be defined as public or private. Primary care refers to the work of professionals who act as a first point of consultation for all patients within the health care system. Depending on the nature of the condition, patients may then be referred for secondary or tertiary care. Primary care is used as the term for the health care services which play a role in the local community. It can be provided in different settings, such as Urgent care centres which provide services to patients same day with appointment or walk-in bases, consequently, a primary care practitioner must possess a wide breadth of knowledge in many areas. The International Classification of Primary Care is a tool for understanding and analyzing information on interventions in primary care by the reason for the patient visit. Common chronic illnesses usually treated in primary care may include, for example, hypertension, diabetes, asthma, COPD, depression and anxiety, back pain, Primary care also includes many basic maternal and child health care services, such as family planning services and vaccinations. Physicians in this model bill patients directly for services, either on a monthly, quarterly, or annual basis. Examples of direct primary care practices include Foundation Health in Colorado, the World Health Organization attributes the provision of essential primary care as an integral component of an inclusive primary health care strategy
10.
Bistatic radar
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Bistatic radar is the name given to a radar system which comprises a transmitter and receiver which are separated by a distance that is comparable to the expected target distance. Conversely, a radar in which the transmitter and receiver are collocated is called a monostatic radar, a system containing multiple spatially diverse monostatic radar or bistatic radar components with a shared area of coverage is called multistatic radar. Many long-range air-to-air and surface-to-air missile systems use semi-active radar homing which is a form of bistatic radar and this is a special case of bistatic radar, known as a forward scatter radar, after the mechanism by which the transmitted energy is scattered by the target. The RCS in this mode is calculated as σ=4πA²/λ², where A is the silhouette area and it is a generalisation of the bistatic radar system, with one or more receivers processing returns from one or more geographically separated transmitter. A bistatic or multistatic radar that exploits non-radar transmitters of opportunity is termed a passive coherent location system or passive covert radar, any radar which does not send active electronic magnetic pulse is known as passive radar. Passive coherent location also known as PCL is a type of passive radar. Bistatic Doppler shift Bistatic angle Bistatic imaging Bistatic range Bistatic sonar
11.
Surface-to-air missile
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A surface-to-air missile, or ground-to-air missile, is a missile designed to be launched from the ground to destroy aircraft or other missiles. It is one type of system, in modern armed forces, missiles have replaced most other forms of dedicated antiaircraft weapons. The first serious attempts at SAM development took place during World War II, further development in the 1940s and 1950s led to the first operational systems being introduced by most major forces during the second half of the 1950s. Smaller systems, suitable for work, evolved through the 1960s and 1970s. The American Nike Ajax was the first operational guided missile SAM system, widely used modern examples include the Patriot and S-300 wide-area systems, SM-6 naval missiles, and short-range man-portable systems like the Stinger and Strela-3. The first known idea for a guided missile was in 1925. A selenium cell was mounted on the tip of each of the rockets four tail fins, when one selenium cell was no longer in the light beam, it would be steered in the opposite direction back into the beam. During World War II, efforts were started to develop surface-to-air missiles as it was considered that flak was of little use against bombers of ever-increasing performance. The lethal radius of a shell is fairly small. Against the Boeing B-17, which operated just within the range of the numerous German eighty-eights flak guns, bombers flying at higher altitudes require larger guns and shells to reach them. This greatly increases the cost of the system, and slows the rate of fire, faster aircraft fly out of range more quickly, reducing the number of rounds fired against them. Against late-war designs like the Boeing B-29 Superfortress or jet-powered designs like the Arado Ar 234, the first serious consideration of a SAM development project was a series of conversations that took place in Germany during 1941. Von Braun became convinced a better solution was a manned rocket interceptor, the directors of the Luftwaffe flak arm were not interested in manned aircraft, and the resulting disagreements between the teams delayed serious consideration of a SAM for two years. None of these saw any real development until 1943, when the first large-scale raids by the Allied air forces started. As the urgency of the problem grew, new designs were added, including Enzian and Rheintochter, in general, these designs could be split into two groups. One set of designs would be boosted to altitude in front of the bombers and these designs included the Feuerlilie, Schmetterling and Enzian. The second group were high-speed missiles, typically supersonic, that flew directly towards their targets from below, both types used radio control for guidance, either by eye, or by comparing the returns of the missile and target on a single radar screen. Development of all systems was carried out at the same time
12.
Weather radar
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Weather radar, also called weather surveillance radar and Doppler weather radar, is a type of radar used to locate precipitation, calculate its motion, and estimate its type. Modern weather radars are mostly pulse-Doppler radars, capable of detecting the motion of rain droplets in addition to the intensity of the precipitation, both types of data can be analyzed to determine the structure of storms and their potential to cause severe weather. During World War II, radar operators discovered that weather was causing echoes on their screen, techniques were developed to filter them, but scientists began to study the phenomenon. Soon after the war, surplus radars were used to detect precipitation, since then, weather radar has evolved on its own and is now used by national weather services, research departments in universities, and in television newscasts. Raw images are used and specialized software can take radar data to make short term forecasts of future positions and intensities of rain, snow, hail. Radar output is even incorporated into weather prediction models to improve analyses. During World War II, military radar operators noticed noise in returned echoes due to rain, snow, after the war, military scientists returned to civilian life or continued in the Armed Forces and pursued their work in developing a use for those echoes. In the United States, David Atlas, at first working for the Air Force and later for MIT, Marshall and R. H. Douglas formed the Stormy Weather Group in Montreal. By 1950 the UK company EKCO was demonstrating its airborne cloud, in 1953 Donald Staggs, an electrical engineer working for the Illinois State Water Survey, made the first recorded radar observation of a hook echo associated with a tornadic thunderstorm. Between 1950 and 1980, reflectivity radars, which measure position, the early meteorologists had to watch a cathode ray tube. During the 1970s, radars began to be standardized and organized into networks, the first devices to capture radar images were developed. The number of scanned angles was increased to get a view of the precipitation, so that horizontal cross-sections. Studies of the organization of thunderstorms were then possible for the Alberta Hail Project in Canada, the NSSL, created in 1964, began experimentation on dual polarization signals and on Doppler effect uses. In May 1973, a tornado devastated Union City, Oklahoma, for the first time, a Dopplerized 10 cm wavelength radar from NSSL documented the entire life cycle of the tornado. The researchers discovered a mesoscale rotation in the cloud aloft before the tornado touched the ground – the tornadic vortex signature, NSSLs research helped convince the National Weather Service that Doppler radar was a crucial forecasting tool. The Super Outbreak of tornadoes on 3–4 April 1974 and their devastating destruction might have helped to get funding for further developments, between 1980 and 2000, weather radar networks became the norm in North America, Europe, Japan and other developed countries. Conventional radars were replaced by Doppler radars, which in addition to position, in the United States, the construction of a network consisting of 10 cm radars, called NEXRAD or WSR-88D, was started in 1988 following NSSLs research. In Canada, Environment Canada constructed the King City station, with a 5 cm research Doppler radar, by 1985 and this led to a complete Canadian Doppler network between 1998 and 2004
13.
Pulse-Doppler radar
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It combines the features of pulse radars and continuous-wave radars, which were formerly separate due to the complexity of the electronics. Pulse-Doppler systems were first widely used on fighter aircraft starting in the 1960s, earlier radars had used pulse-timing in order to determine range and the angle of the antenna to determine the bearing. However, this worked when the radar antenna was not pointed down. As the ground moves at the speed but opposite direction of the aircraft, Doppler techniques allow the ground return to be filtered out, revealing aircraft. This gives pulse-Doppler radars look-down/shoot-down capability, a secondary advantage in military radar is to reduce the transmitted power while achieving acceptable performance for improved safety of stealthy radar. Pulse-Doppler techniques also find use in meteorological radars, allowing the radar to determine wind speed from the velocity of any precipitation in the air. Pulse-Doppler radar is also the basis of synthetic aperture radar used in radar astronomy, in air traffic control, they are used for discriminating aircraft from clutter. The earliest radar systems failed to operate as expected, the reason was traced to Doppler effects that degrade performance of systems not designed to account for moving objects. Fast-moving objects cause a phase-shift on the pulse that can produce signal cancellation. Doppler has maximum effect on moving target indicator systems, which must use reverse phase shift for Doppler compensation in the detector. Doppler weather effects were found to degrade conventional radar and moving target indicator radar. This phenomenon was adapted for use with weather radar in the 1950s after declassification of some World War II systems, Pulse-Doppler radar was developed during World War II to overcome limitations by increasing pulse repetition frequency. This required the development of klystron, the traveling wave tube, Pulse-Doppler is incompatible with other high power microwave amplification devices that are not coherent. Early examples of systems include the AN/SPG-51B developed during the 1950s specifically for the purpose of operating in hurricane conditions with no performance degradation. The USs first pulse-Doppler radar, the system had look-down/shoot-down capability, weather, chaff, terrain, flying techniques, and stealth are common tactics used to hide aircraft from radar. It became possible to use radar on aircraft after digital computers were incorporated in the design. Pulse-Doppler provided look-down/shoot-down capability to support air-to-air missile systems in most modern military aircraft by the mid 1970s, Pulse-Doppler systems measure the range to objects by measuring the elapsed time between sending a pulse of radio energy and receiving a reflection of the object. Radio waves travel at the speed of light, so the distance to the object is the elapsed time multiplied by the speed of light, Pulse-Doppler radar is based on the Doppler effect, where movement in range produces frequency shift on the signal reflected from the target
14.
Precipitation
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In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravity. The main forms of precipitation include drizzle, rain, sleet, snow, graupel, Precipitation occurs when a portion of the atmosphere becomes saturated with water vapor, so that the water condenses and precipitates. Thus, fog and mist are not precipitation but suspensions, because the vapor does not condense sufficiently to precipitate. Two processes, possibly acting together, can lead to air becoming saturated, Precipitation forms as smaller droplets coalesce via collision with other rain drops or ice crystals within a cloud. Short, intense periods of rain in scattered locations are called showers, moisture that is lifted or otherwise forced to rise over a layer of sub-freezing air at the surface may be condensed into clouds and rain. This process is active when freezing rain is occurring. A stationary front is often present near the area of freezing rain, provided necessary and sufficient atmospheric moisture content, the moisture within the rising air will condense into clouds, namely stratus and cumulonimbus. Eventually, the droplets will grow large enough to form raindrops. Lake-effect snowfall can be locally heavy, thundersnow is possible within a cyclones comma head and within lake effect precipitation bands. In mountainous areas, heavy precipitation is possible where upslope flow is maximized within windward sides of the terrain at elevation, on the leeward side of mountains, desert climates can exist due to the dry air caused by compressional heating. The movement of the trough, or intertropical convergence zone. Precipitation is a component of the water cycle, and is responsible for depositing the fresh water on the planet. Approximately 505,000 cubic kilometres of water falls as precipitation each year,398,000 cubic kilometres of it over the oceans and 107,000 cubic kilometres over land. Given the Earths surface area, that means the globally averaged annual precipitation is 990 millimetres, Climate classification systems such as the Köppen climate classification system use average annual rainfall to help differentiate between differing climate regimes. Precipitation may occur on celestial bodies, e. g. when it gets cold, Mars has precipitation which most likely takes the form of frost. Precipitation is a component of the water cycle, and is responsible for depositing most of the fresh water on the planet. Approximately 505,000 km3 of water falls as precipitation each year,398,000 km3 of it over the oceans, given the Earths surface area, that means the globally averaged annual precipitation is 990 millimetres. Mechanisms of producing precipitation include convective, stratiform, and orographic rainfall, Precipitation can be divided into three categories, based on whether it falls as liquid water, liquid water that freezes on contact with the surface, or ice
15.
Christian Doppler
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Christian Andreas Doppler was an Austrian mathematician and physicist. He is celebrated for his principle — known as the Doppler effect — that the frequency of a wave depends on the relative speed of the source. He used this concept to explain the color of binary stars, Christian Doppler was born in Salzburg in Austria in 1803. After completing high school, Doppler studied philosophy in Salzburg and mathematics and physics at the Imperial–Royal Polytechnic Institute where he work as an assistant in 1829. In 1835 he began work at the Prague Polytechnic, where he received an appointment in 1841, there is a facsimile edition with an English translation by Alec Eden. While he worked at the Prague Polytechnic as a professor he published over 50 articles on mathematics, physics and astronomy. In 1847 he left Prague for the professorship of mathematics, physics, and mechanics at the Academy of Mines and Forests in Selmecbánya, Dopplers research was interrupted by the revolutionary incidents of 1848. During the Hungarian Revolution, he fled to Vienna, there he was appointed head of the Institute for Experimental Physics at the University of Vienna in 1850. While there, Doppler, along with Franz Unger, influenced the development of young Gregor Mendel, the father of genetics. Doppler died on 17 March 1853 at age 49 from a disease in Venice. His tomb, found by Dr. Peter M. Schuster is just inside the entrance of the Venetian island cemetery of San Michele, some confusion exists about Dopplers full name. Doppler referred to himself as Christian Doppler, the records of his birth and baptism stated Christian Andreas Doppler. Forty years after Dopplers death the misnomer Johann Christian Doppler was introduced by the astronomer Julius Scheiner, scheiners mistake has since been copied by many. Teil, Helmuth Grössing, Wissenschaft, Leben, Umwelt, Gesellschaft,2, List of Austrian scientists List of Austrians List of minor planets named after people Alec Eden, Christian Doppler, Leben und Werk. The Life of an Unknown Person, Christian Doppler’s Youth in Salzburg and Vienna. In, Ewald Hiebl, Maurizio Musso, Christian Doppler – Life, proceedings of the Commemorative Symposia in Salzburg, Salzburg, Prague, Vienna, Venice. Pöllauberg/Austria, Hainault/UK, Atascadero/US, pages 33 –46, Christian Doppler at Find a Grave OConnor, John J. Robertson, Edmund F. Christian Doppler, MacTutor History of Mathematics archive, University of St Andrews
16.
Frequency
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Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as frequency, which emphasizes the contrast to spatial frequency. The period is the duration of time of one cycle in a repeating event, for example, if a newborn babys heart beats at a frequency of 120 times a minute, its period—the time interval between beats—is half a second. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as vibrations, audio signals, radio waves. For cyclical processes, such as rotation, oscillations, or waves, in physics and engineering disciplines, such as optics, acoustics, and radio, frequency is usually denoted by a Latin letter f or by the Greek letter ν or ν. For a simple motion, the relation between the frequency and the period T is given by f =1 T. The SI unit of frequency is the hertz, named after the German physicist Heinrich Hertz, a previous name for this unit was cycles per second. The SI unit for period is the second, a traditional unit of measure used with rotating mechanical devices is revolutions per minute, abbreviated r/min or rpm. As a matter of convenience, longer and slower waves, such as ocean surface waves, short and fast waves, like audio and radio, are usually described by their frequency instead of period. Spatial frequency is analogous to temporal frequency, but the axis is replaced by one or more spatial displacement axes. Y = sin = sin d θ d x = k Wavenumber, in the case of more than one spatial dimension, wavenumber is a vector quantity. For periodic waves in nondispersive media, frequency has a relationship to the wavelength. Even in dispersive media, the frequency f of a wave is equal to the phase velocity v of the wave divided by the wavelength λ of the wave. In the special case of electromagnetic waves moving through a vacuum, then v = c, where c is the speed of light in a vacuum, and this expression becomes, f = c λ. When waves from a monochrome source travel from one medium to another, their remains the same—only their wavelength. For example, if 71 events occur within 15 seconds the frequency is, the latter method introduces a random error into the count of between zero and one count, so on average half a count. This is called gating error and causes an error in the calculated frequency of Δf = 1/, or a fractional error of Δf / f = 1/ where Tm is the timing interval. This error decreases with frequency, so it is a problem at low frequencies where the number of counts N is small, an older method of measuring the frequency of rotating or vibrating objects is to use a stroboscope
17.
Electromagnetic radiation
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In physics, electromagnetic radiation refers to the waves of the electromagnetic field, propagating through space carrying electromagnetic radiant energy. It includes radio waves, microwaves, infrared, light, ultraviolet, X-, classically, electromagnetic radiation consists of electromagnetic waves, which are synchronized oscillations of electric and magnetic fields that propagate at the speed of light through a vacuum. The oscillations of the two fields are perpendicular to other and perpendicular to the direction of energy and wave propagation. The wavefront of electromagnetic waves emitted from a point source is a sphere, the position of an electromagnetic wave within the electromagnetic spectrum can be characterized by either its frequency of oscillation or its wavelength. Electromagnetic waves are produced whenever charged particles are accelerated, and these waves can interact with other charged particles. EM waves carry energy, momentum and angular momentum away from their source particle, quanta of EM waves are called photons, whose rest mass is zero, but whose energy, or equivalent total mass, is not zero so they are still affected by gravity. Thus, EMR is sometimes referred to as the far field, in this language, the near field refers to EM fields near the charges and current that directly produced them, specifically, electromagnetic induction and electrostatic induction phenomena. In the quantum theory of electromagnetism, EMR consists of photons, quantum effects provide additional sources of EMR, such as the transition of electrons to lower energy levels in an atom and black-body radiation. The energy of a photon is quantized and is greater for photons of higher frequency. This relationship is given by Plancks equation E = hν, where E is the energy per photon, ν is the frequency of the photon, a single gamma ray photon, for example, might carry ~100,000 times the energy of a single photon of visible light. The effects of EMR upon chemical compounds and biological organisms depend both upon the power and its frequency. EMR of visible or lower frequencies is called non-ionizing radiation, because its photons do not individually have enough energy to ionize atoms or molecules, the effects of these radiations on chemical systems and living tissue are caused primarily by heating effects from the combined energy transfer of many photons. In contrast, high ultraviolet, X-rays and gamma rays are called ionizing radiation since individual photons of high frequency have enough energy to ionize molecules or break chemical bonds. These radiations have the ability to cause chemical reactions and damage living cells beyond that resulting from simple heating, Maxwell derived a wave form of the electric and magnetic equations, thus uncovering the wave-like nature of electric and magnetic fields and their symmetry. Because the speed of EM waves predicted by the wave equation coincided with the speed of light. Maxwell’s equations were confirmed by Heinrich Hertz through experiments with radio waves, according to Maxwells equations, a spatially varying electric field is always associated with a magnetic field that changes over time. Likewise, a varying magnetic field is associated with specific changes over time in the electric field. In an electromagnetic wave, the changes in the field are always accompanied by a wave in the magnetic field in one direction
18.
Albert Einstein
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Albert Einstein was a German-born theoretical physicist. He developed the theory of relativity, one of the two pillars of modern physics, Einsteins work is also known for its influence on the philosophy of science. Einstein is best known in popular culture for his mass–energy equivalence formula E = mc2, near the beginning of his career, Einstein thought that Newtonian mechanics was no longer enough to reconcile the laws of classical mechanics with the laws of the electromagnetic field. This led him to develop his theory of relativity during his time at the Swiss Patent Office in Bern. Briefly before, he aquired the Swiss citizenship in 1901, which he kept for his whole life and he continued to deal with problems of statistical mechanics and quantum theory, which led to his explanations of particle theory and the motion of molecules. He also investigated the properties of light which laid the foundation of the photon theory of light. In 1917, Einstein applied the theory of relativity to model the large-scale structure of the universe. He was visiting the United States when Adolf Hitler came to power in 1933 and, being Jewish, did not go back to Germany and he settled in the United States, becoming an American citizen in 1940. This eventually led to what would become the Manhattan Project, Einstein supported defending the Allied forces, but generally denounced the idea of using the newly discovered nuclear fission as a weapon. Later, with the British philosopher Bertrand Russell, Einstein signed the Russell–Einstein Manifesto, Einstein was affiliated with the Institute for Advanced Study in Princeton, New Jersey, until his death in 1955. Einstein published more than 300 scientific papers along with over 150 non-scientific works, on 5 December 2014, universities and archives announced the release of Einsteins papers, comprising more than 30,000 unique documents. Einsteins intellectual achievements and originality have made the word Einstein synonymous with genius, Albert Einstein was born in Ulm, in the Kingdom of Württemberg in the German Empire, on 14 March 1879. His parents were Hermann Einstein, a salesman and engineer, the Einsteins were non-observant Ashkenazi Jews, and Albert attended a Catholic elementary school in Munich from the age of 5 for three years. At the age of 8, he was transferred to the Luitpold Gymnasium, the loss forced the sale of the Munich factory. In search of business, the Einstein family moved to Italy, first to Milan, when the family moved to Pavia, Einstein stayed in Munich to finish his studies at the Luitpold Gymnasium. His father intended for him to electrical engineering, but Einstein clashed with authorities and resented the schools regimen. He later wrote that the spirit of learning and creative thought was lost in strict rote learning, at the end of December 1894, he travelled to Italy to join his family in Pavia, convincing the school to let him go by using a doctors note. During his time in Italy he wrote an essay with the title On the Investigation of the State of the Ether in a Magnetic Field
19.
Special relativity
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In physics, special relativity is the generally accepted and experimentally well-confirmed physical theory regarding the relationship between space and time. In Albert Einsteins original pedagogical treatment, it is based on two postulates, The laws of physics are invariant in all inertial systems, the speed of light in a vacuum is the same for all observers, regardless of the motion of the light source. It was originally proposed in 1905 by Albert Einstein in the paper On the Electrodynamics of Moving Bodies, as of today, special relativity is the most accurate model of motion at any speed. Even so, the Newtonian mechanics model is useful as an approximation at small velocities relative to the speed of light. Not until Einstein developed general relativity, to incorporate general frames of reference, a translation that has often been used is restricted relativity, special really means special case. It has replaced the notion of an absolute universal time with the notion of a time that is dependent on reference frame. Rather than an invariant time interval between two events, there is an invariant spacetime interval, a defining feature of special relativity is the replacement of the Galilean transformations of Newtonian mechanics with the Lorentz transformations. Time and space cannot be defined separately from each other, rather space and time are interwoven into a single continuum known as spacetime. Events that occur at the time for one observer can occur at different times for another. The theory is special in that it applies in the special case where the curvature of spacetime due to gravity is negligible. In order to include gravity, Einstein formulated general relativity in 1915, Special relativity, contrary to some outdated descriptions, is capable of handling accelerations as well as accelerated frames of reference. e. At a sufficiently small scale and in conditions of free fall, a locally Lorentz-invariant frame that abides by special relativity can be defined at sufficiently small scales, even in curved spacetime. Galileo Galilei had already postulated that there is no absolute and well-defined state of rest, Einstein extended this principle so that it accounted for the constant speed of light, a phenomenon that had been recently observed in the Michelson–Morley experiment. He also postulated that it holds for all the laws of physics, Einstein discerned two fundamental propositions that seemed to be the most assured, regardless of the exact validity of the known laws of either mechanics or electrodynamics. These propositions were the constancy of the speed of light and the independence of physical laws from the choice of inertial system, the Principle of Invariant Light Speed –. Light is always propagated in empty space with a definite velocity c which is independent of the state of motion of the emitting body. That is, light in vacuum propagates with the c in at least one system of inertial coordinates. Following Einsteins original presentation of special relativity in 1905, many different sets of postulates have been proposed in various alternative derivations, however, the most common set of postulates remains those employed by Einstein in his original paper
20.
Speed of light
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The speed of light in vacuum, commonly denoted c, is a universal physical constant important in many areas of physics. Its exact value is 299792458 metres per second, it is exact because the unit of length, the metre, is defined from this constant, according to special relativity, c is the maximum speed at which all matter and hence information in the universe can travel. It is the speed at which all particles and changes of the associated fields travel in vacuum. Such particles and waves travel at c regardless of the motion of the source or the reference frame of the observer. In the theory of relativity, c interrelates space and time, the speed at which light propagates through transparent materials, such as glass or air, is less than c, similarly, the speed of radio waves in wire cables is slower than c. The ratio between c and the speed v at which light travels in a material is called the index n of the material. In communicating with distant space probes, it can take minutes to hours for a message to get from Earth to the spacecraft, the light seen from stars left them many years ago, allowing the study of the history of the universe by looking at distant objects. The finite speed of light limits the theoretical maximum speed of computers. The speed of light can be used time of flight measurements to measure large distances to high precision. Ole Rømer first demonstrated in 1676 that light travels at a speed by studying the apparent motion of Jupiters moon Io. In 1865, James Clerk Maxwell proposed that light was an electromagnetic wave, in 1905, Albert Einstein postulated that the speed of light c with respect to any inertial frame is a constant and is independent of the motion of the light source. He explored the consequences of that postulate by deriving the theory of relativity and in doing so showed that the parameter c had relevance outside of the context of light and electromagnetism. After centuries of increasingly precise measurements, in 1975 the speed of light was known to be 299792458 m/s with a measurement uncertainty of 4 parts per billion. In 1983, the metre was redefined in the International System of Units as the distance travelled by light in vacuum in 1/299792458 of a second, as a result, the numerical value of c in metres per second is now fixed exactly by the definition of the metre. The speed of light in vacuum is usually denoted by a lowercase c, historically, the symbol V was used as an alternative symbol for the speed of light, introduced by James Clerk Maxwell in 1865. In 1856, Wilhelm Eduard Weber and Rudolf Kohlrausch had used c for a different constant later shown to equal √2 times the speed of light in vacuum, in 1894, Paul Drude redefined c with its modern meaning. Einstein used V in his original German-language papers on special relativity in 1905, but in 1907 he switched to c, sometimes c is used for the speed of waves in any material medium, and c0 for the speed of light in vacuum. This article uses c exclusively for the speed of light in vacuum, since 1983, the metre has been defined in the International System of Units as the distance light travels in vacuum in 1⁄299792458 of a second
21.
Continuous-wave radar
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Continuous-wave radar is a type of radar system where a known stable frequency continuous-wave radio energy is transmitted and then received from any reflecting objects. Continuous-wave radar uses Doppler, which renders the radar immune to interference from large stationary objects, CW radar systems are used at both ends of the range spectrum. They have no minimum or maximum range, although the broadcast power level imposes a limit on range. Continuous-wave radar maximize total power on a target because the transmitter is broadcasting continuously, the military uses continuous-wave radar to guide semi-active radar homing air-to-air missiles, such as the U. S. AIM-7 Sparrow and standard missile. The launch aircraft illuminates the target with a CW radar signal, since the missile is moving at high velocities relative to the aircraft, there is a strong Doppler shift. Most modern air combat radars, even pulse Doppler sets, have a CW function for missile guidance purposes, maximum distance in a continuous-wave radar is determined by the overall bandwidth and transmitter power. This bandwidth is determined by two factors, transmit energy density Receiver filter size Doubling transmit power increases distance performance by about 20%. Reducing the total FM transmit noise by half has the same effect, frequency domain receivers used for continuous-wave Doppler radar receivers are very different from conventional radar receivers. The receiver consists of a bank of filters, usually more than 100, the number of filters determines the maximum distance performance. Doubling the number of receiver filters increases distance performance by about 20%, maximum distance performance is achieved when receiver filter size is equal to the maximum FM noise riding on the transmit signal. Reducing receiver filter size below average amount of FM transmit noise will not improve range performance, a CW radar is said to be matched when the receiver filter size matches the RMS bandwidth of the FM noise on the transmit signal. There are two types of radar, unmodulated continuous-wave and modulated continuous-wave. This kind of radar can cost less than $100, return frequencies are shifted away from the transmitted frequency based on the Doppler effect when objects are moving. There is no way to evaluate distance and this type of radar is typically used with competition sports, like golf, tennis, baseball, and NASCAR racing. Reflected signals from stationary and slow-moving objects are masked by the transmit signal, frequency-modulated continuous-wave radar – also called continuous-wave frequency-modulated radar – is a short-range measuring radar set capable of determining distance. This increases reliability by providing distance measurement along with speed measurement and this kind of radar is often used as radar altimeter to measure the exact height during the landing procedure of aircraft. It is also used as early-warning radar, wave radar, Doppler shift is not always required for detection when FM is used. In this system the signal of a known stable frequency continuous wave varies up
22.
Continuous wave
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A continuous wave or continuous waveform is an electromagnetic wave of constant amplitude and frequency, a sine wave. In mathematical analysis, it is considered to be of infinite duration, continuous wave is also the name given to an early method of radio transmission, in which a sinusoidal carrier wave is switched on and off. Information is carried in the duration of the on and off periods of the signal. Very early radio transmitters used a gap to produce radio-frequency oscillations in the transmitting antenna. The signals produced by these spark-gap transmitters consisted of strings of brief pulses of radio frequency oscillations which died out rapidly to zero. The disadvantage of damped waves was that their energy was spread over a wide band of frequencies. As a result they produced electromagnetic interference that spread over the transmissions of stations at other frequencies and this motivated efforts to produce radio frequency oscillations that decayed more slowly, had less damping. Manufacturers produced spark transmitters which generated long ringing waves with minimal damping and it was realized that the ideal radio wave for radiotelegraphic communication would be a sine wave with zero damping, a continuous wave. An unbroken continuous sine wave theoretically has no bandwidth, all its energy is concentrated at a single frequency, continuous waves could not be produced with an electric spark, but were achieved with the vacuum tube electronic oscillator, invented around 1913 by Edwin Armstrong and Alexander Meissner. Damped wave spark transmitters were replaced by continuous wave vacuum tube transmitters around 1920, what is transmitted in the extra bandwidth used by a transmitter that turns on/off more abruptly is known as key clicks. Certain types of power used in transmission may increase the effect of key clicks. The first transmitters capable of producing continuous wave, the Alexanderson alternator and vacuum tube oscillators, early radio transmitters could not be modulated to transmit speech, and so CW radio telegraphy was the only form of communication available. Continuous-wave radio was called radiotelegraphy because like the telegraph, it worked by means of a switch to transmit Morse code. However, instead of controlling the electricity in a cross-country wire and this mode is still in common use by amateur radio operators. In military communications and amateur radio, the terms CW and Morse code are used interchangeably. Morse code may be sent using direct current in wires, sound, or light, a carrier wave is keyed on and off to represent the dots and dashes of the code elements. The carriers amplitude and frequency remains constant during each code element, at the receiver, the received signal is mixed with a heterodyne signal from a BFO to change the radio frequency impulses to sound. Though most commercial traffic has now ceased operation using Morse it is popular with amateur radio operators
23.
Frequency modulation
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In telecommunications and signal processing, frequency modulation is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave. This contrasts with amplitude modulation, in which the amplitude of the wave varies. This modulation technique is known as frequency-shift keying, FSK is widely used in modems and fax modems, and can also be used to send Morse code. Frequency modulation is used for FM radio broadcasting. For this reason, most music is broadcast over FM radio, frequency modulation has a close relationship with phase modulation, phase modulation is often used as an intermediate step to achieve frequency modulation. Mathematically both of these are considered a case of quadrature amplitude modulation. While most of the energy of the signal is contained within fc ± fΔ, the frequency spectrum of an actual FM signal has components extending infinitely, although their amplitude decreases and higher-order components are often neglected in practical design problems. Mathematically, a baseband modulated signal may be approximated by a continuous wave signal with a frequency fm. This method is also named as Single-tone Modulation. As in other systems, the modulation index indicates by how much the modulated variable varies around its unmodulated level. e. The maximum deviation of the frequency from the carrier frequency. For a sine wave modulation, the index is seen to be the ratio of the peak frequency deviation of the carrier wave to the frequency of the modulating sine wave. If h ≪1, the modulation is called narrowband FM, sometimes modulation index h<0.3 rad is considered as Narrowband FM otherwise Wideband FM. In the case of digital modulation, the carrier f c is never transmitted, rather, one of two frequencies is transmitted, either f c + Δ f or f c − Δ f, depending on the binary state 0 or 1 of the modulation signal. If h ≫1, the modulation is called wideband FM, if the frequency deviation is held constant and the modulation frequency increased, the spacing between spectra increases. The carrier and sideband amplitudes are illustrated for different modulation indices of FM signals, for particular values of the modulation index, the carrier amplitude becomes zero and all the signal power is in the sidebands. Since the sidebands are on sides of the carrier, their count is doubled, and then multiplied by the modulating frequency to find the bandwidth. For example,3 kHz deviation modulated by a 2.2 kHz audio tone produces an index of 1.36. Suppose that we limit ourselves to only those sidebands that have an amplitude of at least 0.01
24.
Reflectance
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Reflectance of the surface of a material is its effectiveness in reflecting radiant energy. It is the fraction of incident electromagnetic power that is reflected at an interface, the reflectance spectrum or spectral reflectance curve is the plot of the reflectance as a function of wavelength. Hemispherical reflectance of a surface, denoted R, is defined as R = Φ e r Φ e i, where Φer is the radiant flux reflected by that surface, Φei is the radiant flux received by that surface. Directional reflectance of a surface, denoted RΩ, is defined as R Ω = L e, Ω r L e, Ω i, for homogeneous and semi-infinite materials, reflectivity is the same as reflectance. For layered and finite media, according to the CIE, reflectivity is distinguished from reflectance by the fact that reflectivity is a value that applies to thick reflecting objects. When reflection occurs from thin layers of material, internal reflection effects can cause the reflectance to vary with surface thickness, such surfaces are said to be Lambertian. Most real objects have some mixture of diffuse and specular reflective properties, reflection occurs when light moves from a medium with one index of refraction into a second medium with a different index of refraction. Specular reflection from a body of water is calculated by the Fresnel equations, Fresnel reflection is directional and therefore does not contribute significantly to albedo which is primarily diffuse reflection. A real water surface may be wavy, Reflectance assuming a flat surface as given by the Fresnel equations can be adjusted to account for waviness. The generalization of reflectance to a diffraction grating, which disperses light by wavelength, is called diffraction efficiency, Reflectance is an important concept in the fields of optics, solar thermal energy, telecommunication and radar. Bidirectional reflectance distribution function Emissivity Lamberts cosine law Transmittance Sun path Light Reflectance Value Albedo Reflectivity of metals
25.
World War II
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World War II, also known as the Second World War, was a global war that lasted from 1939 to 1945, although related conflicts began earlier. It involved the vast majority of the worlds countries—including all of the great powers—eventually forming two opposing alliances, the Allies and the Axis. It was the most widespread war in history, and directly involved more than 100 million people from over 30 countries. Marked by mass deaths of civilians, including the Holocaust and the bombing of industrial and population centres. These made World War II the deadliest conflict in human history, from late 1939 to early 1941, in a series of campaigns and treaties, Germany conquered or controlled much of continental Europe, and formed the Axis alliance with Italy and Japan. Under the Molotov–Ribbentrop Pact of August 1939, Germany and the Soviet Union partitioned and annexed territories of their European neighbours, Poland, Finland, Romania and the Baltic states. In December 1941, Japan attacked the United States and European colonies in the Pacific Ocean, and quickly conquered much of the Western Pacific. The Axis advance halted in 1942 when Japan lost the critical Battle of Midway, near Hawaii, in 1944, the Western Allies invaded German-occupied France, while the Soviet Union regained all of its territorial losses and invaded Germany and its allies. During 1944 and 1945 the Japanese suffered major reverses in mainland Asia in South Central China and Burma, while the Allies crippled the Japanese Navy, thus ended the war in Asia, cementing the total victory of the Allies. World War II altered the political alignment and social structure of the world, the United Nations was established to foster international co-operation and prevent future conflicts. The victorious great powers—the United States, the Soviet Union, China, the United Kingdom, the Soviet Union and the United States emerged as rival superpowers, setting the stage for the Cold War, which lasted for the next 46 years. Meanwhile, the influence of European great powers waned, while the decolonisation of Asia, most countries whose industries had been damaged moved towards economic recovery. Political integration, especially in Europe, emerged as an effort to end pre-war enmities, the start of the war in Europe is generally held to be 1 September 1939, beginning with the German invasion of Poland, Britain and France declared war on Germany two days later. The dates for the beginning of war in the Pacific include the start of the Second Sino-Japanese War on 7 July 1937, or even the Japanese invasion of Manchuria on 19 September 1931. Others follow the British historian A. J. P. Taylor, who held that the Sino-Japanese War and war in Europe and its colonies occurred simultaneously and this article uses the conventional dating. Other starting dates sometimes used for World War II include the Italian invasion of Abyssinia on 3 October 1935. The British historian Antony Beevor views the beginning of World War II as the Battles of Khalkhin Gol fought between Japan and the forces of Mongolia and the Soviet Union from May to September 1939, the exact date of the wars end is also not universally agreed upon. It was generally accepted at the time that the war ended with the armistice of 14 August 1945, rather than the formal surrender of Japan
26.
United States Navy
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The United States Navy is the naval warfare service branch of the United States Armed Forces and one of the seven uniformed services of the United States. The U. S. Navy is the largest, most capable navy in the world, the U. S. Navy has the worlds largest aircraft carrier fleet, with ten in service, two in the reserve fleet, and three new carriers under construction. The service has 323,792 personnel on duty and 108,515 in the Navy Reserve. It has 274 deployable combat vessels and more than 3,700 operational aircraft as of October 2016, the U. S. Navy traces its origins to the Continental Navy, which was established during the American Revolutionary War and was effectively disbanded as a separate entity shortly thereafter. It played a role in the American Civil War by blockading the Confederacy. It played the role in the World War II defeat of Imperial Japan. The 21st century U. S. Navy maintains a global presence, deploying in strength in such areas as the Western Pacific, the Mediterranean. The Navy is administratively managed by the Department of the Navy, the Department of the Navy is itself a division of the Department of Defense, which is headed by the Secretary of Defense. The Chief of Naval Operations is an admiral and the senior naval officer of the Department of the Navy. The CNO may not be the highest ranking officer in the armed forces if the Chairman or the Vice Chairman of the Joint Chiefs of Staff. The mission of the Navy is to maintain, train and equip combat-ready Naval forces capable of winning wars, deterring aggression, the United States Navy is a seaborne branch of the military of the United States. The Navys three primary areas of responsibility, The preparation of naval forces necessary for the prosecution of war. The development of aircraft, weapons, tactics, technique, organization, U. S. Navy training manuals state that the mission of the U. S. Armed Forces is to prepare and conduct prompt and sustained combat operations in support of the national interest, as part of that establishment, the U. S. Navys functions comprise sea control, power projection and nuclear deterrence, in addition to sealift duties. It follows then as certain as that night succeeds the day, that without a decisive naval force we can do nothing definitive, the Navy was rooted in the colonial seafaring tradition, which produced a large community of sailors, captains, and shipbuilders. In the early stages of the American Revolutionary War, Massachusetts had its own Massachusetts Naval Militia, the establishment of a national navy was an issue of debate among the members of the Second Continental Congress. Supporters argued that a navy would protect shipping, defend the coast, detractors countered that challenging the British Royal Navy, then the worlds preeminent naval power, was a foolish undertaking. Commander in Chief George Washington resolved the debate when he commissioned the ocean-going schooner USS Hannah to interdict British merchant ships, and reported the captures to the Congress
27.
Ultra high frequency
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Ultra high frequency is the ITU designation for radio frequencies in the range between 300 MHz and 3 GHz, also known as the decimetre band as the wavelengths range from one meter to one decimetre. Radio waves with frequencies above the UHF band fall into the SHF or microwave frequency range, lower frequency signals fall into the VHF or lower bands. UHF radio waves propagate mainly by line of sight, they are blocked by hills, the IEEE defines the UHF radar band as frequencies between 300 MHz and 1 GHz. Two other IEEE radar bands overlap the ITU UHF band, the L band between 1 and 2 GHz and the S band between 2 and 4 GHz. Radio waves in the UHF band travel almost entirely by propagation and ground reflection, there is very little reflection from the ionosphere. They are blocked by hills and cannot travel far beyond the horizon, atmospheric moisture reduces, or attenuates, the strength of UHF signals over long distances, and the attenuation increases with frequency. UHF TV signals are generally more degraded by moisture than lower bands, occasionally when conditions are right, UHF radio waves can travel long distances by tropospheric ducting as the atmosphere warms and cools throughout the day. The length of an antenna is related to the length of the radio waves used, the UHF antenna is stubby and short, at UHF frequencies a quarter-wave monopole, the most common omnidirectional antenna is between 2.5 and 25 cm long for example. UHF is widely used in telephones, cell phones, walkie-talkies and other two-way radio systems from short range up to the visual horizon. Their transmissions do not travel far, allowing frequency reuse, public safety, business communications and personal radio services such as GMRS, PMR446, and UHF CB are often found on UHF frequencies as well as IEEE802.11 wireless LANs. The widely adapted GSM and UMTS cellular networks use UHF cellular frequencies, radio repeaters are used to retransmit UHF signals when a distance greater than the line of sight is required. Omnidirectional UHF antennas used on mobile devices are usually short whips, higher gain omnidirectional UHF antennas can be made of collinear arrays of dipoles and are used for mobile base stations and cellular base station antennas. The short wavelengths also allow high gain antennas to be conveniently small, high gain antennas for point-to-point communication links and UHF television reception are usually Yagi, log periodic, corner reflectors, or reflective array antennas. At the top end of the band slot antennas and parabolic dishes become practical, for television broadcasting specialized vertical radiators that are mostly modifications of the slot antenna or helical antenna are used, the slotted cylinder, zig-zag, and panel antennas. UHF television broadcasting fulfilled the demand for additional over-the-air television channels in urban areas, today, much of the bandwidth has been reallocated to land mobile, trunked radio and mobile telephone use. UHF channels are used for digital television. UHF spectrum is used worldwide for mobile radio systems for commercial, industrial, public safety. Many personal radio services use frequencies allocated in the UHF band, major telecommunications providers have deployed voice and data cellular networks in UHF/VHF range
28.
Port and starboard
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Port and starboard are nautical and aeronautical terms for left and right, respectively. Port is the side of a vessel or aircraft, facing forward. Starboard is the side, facing forward. Since port and starboard never change, they are references that are not relative to the observer. These terms are also being used as aeronautic terms, the term starboard derives from the Old English steorbord, meaning the side on which the ship is steered. Before ships had rudders on their centrelines, they were steered with an oar at the stern of the ship and, because more people are right-handed. The term is cognate with the Old Norse stýri and borð, since the steering oar was on the right side of the boat, it would tie up at wharf on the other side. Hence the left side was called port, formerly, larboard was used instead of port. This is from Middle-English ladebord and the lade is related to the modern load. Larboard sounds similar to starboard and in 1844 the Royal Navy ordered that port be used instead, the United States Navy followed suit in 1846. Larboard continued to be used well into the 1850s by whalers, in Old English the word was bæcbord, of which cognates are used in other European languages, for example as the present Dutch bakboord, the German backbord and the French term bâbord. Aircraft are lit in the same way
29.
Bomber
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A bomber is a combat aircraft designed to attack ground and sea targets by dropping air-to-ground weaponry, firing torpedoes or deploying air-launched cruise missiles. In 1912, during the First Balkan War, Bulgarian Air Force pilot Christo Toprakchiev suggested the use of aircraft to drop bombs on Turkish positions, captain Simeon Petrov developed the idea and created several prototypes by adapting different types of grenades and increasing their payload. This is deemed to be the first use of an aircraft as a bomber, the first heavier-than-air aircraft purposely designed for bombing were the Italian Caproni Ca 30 and British Bristol T. B.8, both of 1913. The Bristol T. B.8 was an early British single engined biplane built by the Bristol Aeroplane Company, under the command of Charles Rumney Samson, a bombing attack on German gun batteries at Middelkerke, Belgium was executed on 25 November 1914. The dirigible, or airship, was developed in the early 20th century, early airships were prone to disaster, but slowly the airship became more dependable, with a more rigid structure and stronger skin. Prior to the outbreak of war, Zeppelins, a larger and these were the first long range, strategic bombers. Although the German air arm was strong, with a total of 123 airships by the end of the war, they were vulnerable to attack and engine failure, German airships inflicted little damage on all 51 raids, with 557 Britons killed and 1,358 injured. The German Navy lost 53 of its 73 airships, and the German Army lost 26 of its 50 ships, the Caproni Ca 30 was built by Gianni Caproni in Italy. It was a biplane with three 67 kW Gnome rotary engines and first flew in October 1914. Test flights revealed power to be insufficient and the engine layout unworkable, the improved design was bought by the Italian Army and it was delivered in quantity from August 1915. Bombing raids and interdiction operations were carried out by French. Sustained attacks with a view to interrupting the enemys railway communications, in conjunction with the main operations of the Allied Armies. The most important bombers used in World War I were the French Breguet 14, British de Havilland DH-4, German Albatros C. III, the Russian Sikorsky Ilya Muromets, was the first four-engine bomber to equip a dedicated strategic bombing unit during World War I. This heavy bomber was unrivaled in the stages of the war. With engine power as a limitation, combined with the desire for accuracy and other operational factors. By the start of the war included, dive bomber — specially strengthened for vertical diving attacks for greater accuracy. Light bomber, medium bomber and heavy bomber — subjective definitions based on size, torpedo bomber — specialized aircraft armed with torpedoes. Ground attack aircraft — aircraft used against targets on a such as troop or tank concentrations
30.
Semi-active radar homing
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Semi-active radar homing is a common type of missile guidance system, perhaps the most common type for longer-range air-to-air and surface-to-air missile systems. The name refers to the fact that the missile itself is only a passive detector of a radar signal – provided by an external source — as it reflects off the target, semi-active missile systems use bistatic continuous-wave radar. The NATO brevity code for a semi-active radar homing missile launch is Fox One, the basic concept of SARH is that since almost all detection and tracking systems consist of a radar system, duplicating this hardware on the missile itself is redundant. The weight of a transmitter reduces the range of any flying object, additionally, the missile will listen rearward to the launch platforms transmitted signal as a reference, enabling it to avoid some kinds of radar jamming distractions offered by the target. The SARH system determines the closing velocity using the flight path geometry shown in Figure 1, the closing velocity is used to set the frequency location for the CW receive signal shown at the bottom of the diagram. Antenna offset angle of the antenna is set after the target is acquired by the missile seeker using the spectrum location set using closing speed. The missile seeker antenna is a radar receiver that produces angle error measurements using that fixed position. Flight path is controlled by producing navigation input to the system using angle errors produced by the antenna. This steers the body of the missile to hold the target near the centerline of the antenna while the antenna is held in a fixed position, the offset angle geometry is determined by flight dynamics using missile speed, target speed, and separation distance. Techniques are nearly identical using jamming signals, optical guidance video, maximum range is increased in SARH systems using navigation data in the homing vehicle to increase the travel distance before antenna tracking is needed for terminal guidance. Navigation relies on data, gyroscopic data, and global positioning data. This maximizes distance by minimizing corrective maneuvers that waste flight energy, in the SARH system the missile listens for the reflected signal at the nose, and is still responsible for providing some sort of “lead” guidance. The disadvantages of beam riding are twofold, One is that a signal is “fan shaped”, growing larger. Reduced accuracy means the missile must use a large warhead to be effective. Another requirement is that a beam riding system must accurately track the target at speeds, typically requiring one radar for tracking. The SARH system needs only one set to a wider pattern. Modern SARH systems use continuous-wave radar for guidance, even though most modern fighter radars are pulse Doppler sets, most have a CW function to guide radar missiles. A few Soviet aircraft, such as versions of the MiG-23 and MiG-27
31.
Fast Fourier transform
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A fast Fourier transform algorithm computes the discrete Fourier transform of a sequence, or its inverse. Fourier analysis converts a signal from its domain to a representation in the frequency domain. An FFT rapidly computes such transformations by factorizing the DFT matrix into a product of sparse factors. As a result, it manages to reduce the complexity of computing the DFT from O, which if one simply applies the definition of DFT, to O. Fast Fourier transforms are used for many applications in engineering, science. The basic ideas were popularized in 1965, but some algorithms had been derived as early as 1805, the DFT is obtained by decomposing a sequence of values into components of different frequencies. This operation is useful in many fields but computing it directly from the definition is too slow to be practical. The difference in speed can be enormous, especially for data sets where N may be in the thousands or millions. In practice, the time can be reduced by several orders of magnitude in such cases. The best-known FFT algorithms depend upon the factorization of N, but there are FFTs with O complexity for all N, even for prime N. Since the inverse DFT is the same as the DFT, but with the sign in the exponent. The development of fast algorithms for DFT can be traced to Gausss unpublished work in 1805 when he needed it to interpolate the orbit of asteroids Pallas and Juno from sample observations. His method was similar to the one published in 1965 by Cooley and Tukey. While Gausss work predated even Fouriers results in 1822, he did not analyze the computation time, between 1805 and 1965, some versions of FFT were published by other authors. Yates in 1932 published his version called interaction algorithm, which provided efficient computation of Hadamard, yates algorithm is still used in the field of statistical design and analysis of experiments. In 1942, Danielson and Lanczos published their version to compute DFT for x-ray crystallography, Cooley and Tukey published a more general version of FFT in 1965 that is applicable when N is composite and not necessarily a power of 2. To analyze the output of these sensors, a fast Fourier transform algorithm would be needed, garwin gave Tukeys idea to Cooley for implementation. Cooley and Tukey published the paper in a short six months
32.
Microprocessor
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A microprocessor is a computer processor which incorporates the functions of a computers central processing unit on a single integrated circuit, or at most a few integrated circuits. Microprocessors contain both combinational logic and sequential digital logic, Microprocessors operate on numbers and symbols represented in the binary numeral system. The integration of a whole CPU onto a chip or on a few chips greatly reduced the cost of processing power. Integrated circuit processors are produced in numbers by highly automated processes resulting in a low per unit cost. Single-chip processors increase reliability as there are many electrical connections to fail. As microprocessor designs get better, the cost of manufacturing a chip generally stays the same, before microprocessors, small computers had been built using racks of circuit boards with many medium- and small-scale integrated circuits. Microprocessors combined this into one or a few large-scale ICs, the internal arrangement of a microprocessor varies depending on the age of the design and the intended purposes of the microprocessor. Advancing technology makes more complex and powerful chips feasible to manufacture, a minimal hypothetical microprocessor might only include an arithmetic logic unit and a control logic section. The ALU performs operations such as addition, subtraction, and operations such as AND or OR, each operation of the ALU sets one or more flags in a status register, which indicate the results of the last operation. The control logic retrieves instruction codes from memory and initiates the sequence of operations required for the ALU to carry out the instruction, a single operation code might affect many individual data paths, registers, and other elements of the processor. As integrated circuit technology advanced, it was feasible to manufacture more and more complex processors on a single chip, the size of data objects became larger, allowing more transistors on a chip allowed word sizes to increase from 4- and 8-bit words up to todays 64-bit words. Additional features were added to the architecture, more on-chip registers sped up programs. Floating-point arithmetic, for example, was not available on 8-bit microprocessors. Integration of the point unit first as a separate integrated circuit and then as part of the same microprocessor chip. Occasionally, physical limitations of integrated circuits made such practices as a bit slice approach necessary, instead of processing all of a long word on one integrated circuit, multiple circuits in parallel processed subsets of each data word. With the ability to put large numbers of transistors on one chip and this CPU cache has the advantage of faster access than off-chip memory, and increases the processing speed of the system for many applications. Processor clock frequency has increased more rapidly than external memory speed, except in the recent past, a microprocessor is a general purpose system. Several specialized processing devices have followed from the technology, A digital signal processor is specialized for signal processing, graphics processing units are processors designed primarily for realtime rendering of 3D images
33.
Air traffic control
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The primary purpose of ATC worldwide is to prevent collisions, organize and expedite the flow of air traffic, and provide information and other support for pilots. In some countries, ATC plays a security or defensive role, to prevent collisions, ATC enforces traffic separation rules, which ensure each aircraft maintains a minimum amount of empty space around it at all times. Many aircraft also have collision avoidance systems, which provide additional safety by warning pilots when other aircraft get too close, in many countries, ATC provides services to all private, military, and commercial aircraft operating within its airspace. Depending on the type of flight and the class of airspace, ATC may issue instructions that pilots are required to obey, or advisories that pilots may, at their discretion, disregard. Pursuant to requirements of the International Civil Aviation Organization, ATC operations are conducted either in the English language or the used by the station on the ground. In practice, the language for a region is normally used, however. In 1921, Croydon Airport, London was the first airport in the world to air traffic control. In the United States, air traffic control developed three divisions, the first of air mail radio stations was created in 1922 after World War I when the U. S. Post Office began using techniques developed by the Army to direct, over time, the AMRS morphed into flight service stations. Todays flight service stations do not issue instructions, but provide pilots with many other flight related informational services. They do relay control instructions from ATC in areas where service is the only facility with radio or phone coverage. The first airport traffic control tower, regulating arrivals, departures and surface movement of aircraft at a specific airport, approach/departure control facilities were created after adoption of radar in the 1950s to monitor and control the busy airspace around larger airports. The first air traffic control center, which directs the movement of aircraft between departure and destination was opened in Newark, NJ in 1935, followed in 1936 by Chicago. The primary method of controlling the airport environment is visual observation from the airport control tower. The tower is a tall, windowed structure located on the airport grounds, surveillance displays are also available to controllers at larger airports to assist with controlling air traffic. Controllers may use a system called secondary surveillance radar for airborne traffic approaching and departing. These displays include a map of the area, the position of aircraft, and data tags that include aircraft identification, speed, altitude. In adverse weather conditions the tower controllers may also use surface movement radar, surface movement guidance, remote and virtual tower is a system based on air traffic controllers being located somewhere other than at the local airport tower and still able to provide air traffic control services
34.
Mach number
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In fluid dynamics, the Mach number is a dimensionless quantity representing the ratio of flow velocity past a boundary to the local speed of sound. M = u c, where, M is the Mach number, u is the flow velocity with respect to the boundaries. By definition, Mach 1 is equal to the speed of sound, Mach 0.65 is 65% of the speed of sound, and Mach 1.35 is 35% faster than the speed of sound. The local speed of sound, and thereby the Mach number, depends on the condition of the surrounding medium, the Mach number is primarily used to determine the approximation with which a flow can be treated as an incompressible flow. The medium can be a gas or a liquid, the boundary can be the boundary of an object immersed in the medium, or of a channel such as a nozzle, diffusers or wind tunnels channeling the medium. As the Mach number is defined as the ratio of two speeds, it is a dimensionless number, if M <0. 2–0.3 and the flow is quasi-steady and isothermal, compressibility effects will be small and simplified incompressible flow equations can be used. The Mach number is named after Austrian physicist and philosopher Ernst Mach, as the Mach number is a dimensionless quantity rather than a unit of measure, with Mach, the number comes after the unit, the second Mach number is Mach 2 instead of 2 Mach. This is somewhat reminiscent of the modern ocean sounding unit mark, which was also unit-first. In the decade preceding faster-than-sound human flight, aeronautical engineers referred to the speed of sound as Machs number, never Mach 1, Mach number is useful because the fluid behaves in a similar manner at a given Mach number, regardless of other variables. As modeled in the International Standard Atmosphere, dry air at sea level, standard temperature of 15 °C. For example, the atmosphere model lapses temperature to −56.5 °C at 11,000 meters altitude. In the following table, the regimes or ranges of Mach values are referred to, generally, NASA defines high hypersonic as any Mach number from 10 to 25, and re-entry speeds as anything greater than Mach 25. Aircraft operating in this include the Space Shuttle and various space planes in development. Flight can be classified in six categories, For comparison. At transonic speeds, the field around the object includes both sub- and supersonic parts. The transonic period begins when first zones of M >1 flow appear around the object, in case of an airfoil, this typically happens above the wing. Supersonic flow can decelerate back to only in a normal shock. As the speed increases, the zone of M >1 flow increases towards both leading and trailing edges
35.
Knot (unit)
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The knot is a unit of speed equal to one nautical mile per hour, approximately 1.151 mph. The ISO Standard symbol for the knot is kn, the same symbol is preferred by the IEEE, kt is also common. The knot is a unit that is accepted for use with the SI. Etymologically, the term derives from counting the number of knots in the line that unspooled from the reel of a log in a specific time. 1 international knot =1 nautical mile per hour,1.852 kilometres per hour,0.514 metres per second,1.151 miles per hour,20.254 inches per second,1852 m is the length of the internationally agreed nautical mile. The US adopted the definition in 1954, having previously used the US nautical mile. The UK adopted the international nautical mile definition in 1970, having used the UK Admiralty nautical mile. The speeds of vessels relative to the fluids in which they travel are measured in knots, for consistency, the speeds of navigational fluids are also measured in knots. Thus, speed over the ground and rate of progress towards a distant point are given in knots. Until the mid-19th century, vessel speed at sea was measured using a chip log, the chip log was cast over the stern of the moving vessel and the line allowed to pay out. Knots placed at a distance of 8 fathoms -47 feet 3 inches from each other, passed through a sailors fingers, the knot count would be reported and used in the sailing masters dead reckoning and navigation. This method gives a value for the knot of 20.25 in/s, the difference from the modern definition is less than 0. 02%. On a chart of the North Atlantic, the scale varies by a factor of two from Florida to Greenland, a single graphic scale, of the sort on many maps, would therefore be useless on such a chart. Recent British Admiralty charts have a latitude scale down the middle to make this even easier, speed is sometimes incorrectly expressed as knots per hour, which is in fact a measure of acceleration. Prior to 1969, airworthiness standards for aircraft in the United States Federal Aviation Regulations specified that distances were to be in statute miles. In 1969, these standards were amended to specify that distances were to be in nautical miles. At 11000 m, an airspeed of 300 kn may correspond to a true airspeed of 500 kn in standard conditions. Beaufort scale Hull speed, which deals with theoretical estimates of maximum speed of displacement hulls Knot count Knotted cord Metre per second Orders of magnitude Rope Kemp
36.
Circulator
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A circulator is a passive non-reciprocal three- or four-port device, in which a microwave or radio frequency signal entering any port is transmitted to the next port in rotation. A port in this context is a point where an external waveguide or transmission line, Ferrite circulators are radio frequency circulators which are composed of magnetised ferrite materials. Waveguide circulators may be of type, while more compact devices based on stripline are of the 3-port type. Two or more Y-junctions can be combined in a component to give four or more ports. A permanent magnet produces the magnetic flux through the waveguide, ferrimagnetic garnet crystal is used in optical circulators. Early work on nonferrite circulators includes active circulators using transistors that are non-reciprocal in nature, in contrast to ferrite circulators which are passive devices, active circulators require power. One study employed a similar to a time-varying transmission line with the effective nonreciprocity triggered by a one-direction propagating carrier pump. This is like an AC-powered active circulator, the research claimed to be able to achieve positive gain and low noise for receiving path and broadband nonreciprocity. Another study used resonance with nonreciprocity triggered by angular-momentum biasing, which more closely mimics the way that signals passively circulate in a ferrite circulator, in April,2016 a research team presented an integrated circuit circulator based on N-path filter concepts. It offers the potential for full duplex communication, the device uses capacitors and a clock and is much smaller than conventional devices. When one port of a three-port circulator is terminated in a load, it can be used as an isolator. An isolator is used to shield equipment on its side from the effects of conditions on its output side, for example. The alternative type of duplexer is a switch that alternates between connecting the antenna to the transmitter and to the receiver. The use of chirped pulses and a dynamic range may lead to temporal overlap of the sent and received pulses, however. In the future-generation cellular communication, people talk about full-duplex radios, given the currently limited, crowded spectrum resource, full-duplexing can directly benefit the wireless communication by twice of the data throughput speed. A reflection amplifier is a type of microwave amplifier circuit utilizing negative differential resistance diodes such as tunnel diodes, negative differential resistance diodes can amplify signals, and often perform better at microwave frequencies than two-port devices. However, since the diode is a device, a nonreciprocal component is needed to separate the outgoing amplified signal from the incoming input signal. By using a 3-port circulator with the signal input connected to one port, the biased diode connected to a second, and the load connected to the third
37.
Radar navigation
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Marine and aviation radar systems can provide very useful navigation information in a variety of situations. A fix consisting of radar information is called a radar fix. Some types of radar fixes include the relatively self-explanatory methods of range and bearing to a single object, parallel indexing is a technique defined by William Burger in the 1957 book The Radar Observers Handbook. This technique involves creating a line on the screen that is parallel to the ships course and this parallel line allows the navigator to maintain a given distance away from hazards. Some techniques have developed for special situations. One, known as the method, involves marking a transparent plastic template on the radar screen. Another special technique, known as the Franklin Continuous Radar Plot Technique, during the transit, the navigator can check that the ship is on track by checking that the pip lies on the drawn line. After completing the plotting radar technique, the image from the radar can either be displayed, captured or recorded to a monitor using a frame grabber. Bethesda, MD, National Imagery and Mapping Agency, cutler, Thomas J. Duttons Nautical Navigation. Maloney, Elbert S. Chapman Piloting and Seamanship, new York, NY, Hearst Communications Inc. Publication 1310, Radar Navigation and Maneuvering Board Manual, bethesda, MD, U. S. Government Printing Office
38.
National Electronics Museum
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The National Electronics Museum, located in Linthicum, Maryland, displays the history of the United States defense electronics. The National Electronics Museum houses exhibits containing assortments of telegraphs, radios, radars, admission is $5 for adults, $3 for seniors and students, and children under 5 years of age are free. Located near the Baltimore Washington International Airport and rail station, the museum displays hands-on electronics, the library serves as a research center open to the public. Hours are Monday through Friday 09, 00am -4, 00pm. and Saturday 10, 00am -2, in addition, an amateur radio station is broadcast live from the museum each week. K3NEM/W3GR includes both antique and updated communication equipment, early Radar Gallery- Radar from World War II Cold War Radar Gallery- The Cold War advanced technology in many areas, including radar. The current Exhibit examines the history of Apple Computers, outside Gallery – Six Historic radar Antennas, spanning 75 years of radar development, stand around the museum. RobotFest - held at the museum annually Pioneer Camp - held at the museum each summer The National Electronics museum was created by Westinghouse employees. Titled “Yesterday, Today, and Tomorrow”, the exhibit showed examples of past, Dwight then decided to pursue more radar systems and other electronics for viewing. His first mission, taken on with the help of Jack Sun and this missile housed the first airborne pulse-doppler radar, AN/DPN-53. However, in order to access to the radar they had to be classified as a non-profit museum. After gaining advice and paperwork from Westinghouse lawyer, Butch Gregory, finances and storage space were handled by Westinghouse, and in 1983 a 190 m² portion of space was devoted to the museum at the Airport Square III. Then, in 1986 the space was extended to 370 m², formerly run by volunteers, the museum hired its first professional employee in 1992 when it was relocated to Friendship square. In 1996, Northrop Grumman bought Westinghouse and continued support for museum efforts, the museum closed its doors temporarily when it underwent construction in 1999 and reopened with over 2000 m² of space. This space included a room, event hall, gallery. The museum offers programs such as YESS and the annual Robot Fest. Donations and grants are accepted from foundations and engineering societies, board members include former Westinghouse employees and Northrop Grumman associates. Over 30 volunteers donate over 5,000 hours of their time each year
39.
Dead reckoning
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The corresponding term in biology, used to describe the processes by which animals update their estimates of position or heading, is path integration. Dead reckoning is subject to cumulative errors, however, inertial navigation systems, which provide very accurate directional information, use dead reckoning and are very widely applied. Often, this implies that the changes are not known accurately. The earlier value and the changes may be measured or calculated quantities, there is speculation on the origin of the term, but no reliable information. As each estimate of position is relative to the one, errors are cumulative, or compounding, multiplicatively or exponentially. The accuracy of dead reckoning can be increased significantly by using other, localizing a static sensor node is not a difficult task because attaching a GPS device suffices the need of localization. But a mobile sensor node, which change its geographical location with time is difficult to localize. Mostly mobile sensor nodes within some particular domain for data collection can be used, i. e, within these scenarios a GPS device for each sensor node cannot be afforded. Some of the reasons for this include cost, size and battery drainage of constrained sensor nodes, to overcome this problem a limited number of reference nodes within a field is employed. These nodes continuously broadcast their locations and other nodes in proximity receive these locations, for localization, at least three known reference locations are necessary to localize. Several localization algorithms based on Sequential Monte Carlo method have been proposed in literatures, sometimes a node at some places receives only two known locations and hence it becomes impossible to localize. To overcome this problem, dead reckoning technique is used, with this technique a sensor node uses its previous calculated location for localization at later time intervals. This not only localizes a node in less time but also localizes in positions where it is difficult to get three reference locations, in studies of animal navigation, dead reckoning is more commonly known as path integration. Animals use it to estimate their current location based on their movements from their last known location. Animals such as ants, rodents, and geese have been shown to track their locations relative to a starting point and to return to it. In marine navigation a dead reckoning plot generally does not take account the effect of currents or wind. Aboard ship a dead reckoning plot is considered important in evaluating position information, dead reckoning begins with a known position, or fix, which is then advanced, mathematically or directly on the chart, by means of recorded heading, speed, and time. Speed can be determined by many methods, before modern instrumentation, it was determined aboard ship using a chip log
40.
English Electric Canberra
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The English Electric Canberra is a British first-generation jet-powered medium bomber that was manufactured during the 1950s. It was developed by English Electric during the mid-to-late 1940s in response to a 1944 Air Ministry requirement for a successor to the wartime de Havilland Mosquito fast-bomber. Amongst the performance requirements for the type was the demand for a high altitude bombing capability in addition to flying at high speeds. These were partly accomplished by making use of newly developed jet propulsion technology, when the Canberra was introduced to service with the Royal Air Force, the types first operator, in May 1951, it became the services first jet-powered bomber aircraft. Throughout the majority of the 1950s, the Canberra could fly at a higher altitude than any other bomber or even any other aircraft in the world, in 1957, one Canberra established a world altitude record of 70,310 ft. In February 1951, another Canberra set another record when it became the first jet aircraft to make a non-stop transatlantic flight. The type was also produced in Australia and the United States of America. In addition to being a nuclear strike aircraft, the Canberra proved to be highly adaptable, serving in varied roles such as tactical bombing. Canberras served in the Suez Crisis, the Vietnam War, the Falklands War, the Indo-Pakistani wars, in several wars, each of the opposing sides had Canberras in their air forces. The Canberra had a service life, serving for more than 50 years with some operators. In June 2006, the RAF retired the last of its Canberras,57 years after its first flight, three of the Martin B-57 variant remain in service, performing meteorological work for NASA, as well as providing electronic communication testing for deployment to Afghanistan. During the Second World War, a demand for bomber aircraft led to many aircraft being produced by secondary manufacturers via licence manufacturing arrangements. Sir George Nelson, the chairman of English Electric, decided that the company would seek to remain in the business, in November 1943, the company was invited to participate in discussions over a prospective bomber which would take advantage of the newly developed jet propulsion technology. The design used a conventional aerodynamic design, Petter having determined that the necessary performance could be attained without adopting swept wings or a swept tail. The authorities doubted its suitability for operations from unprepared fields and at low altitude but could see its potential as a bomber design, numerous manufacturers refused to take on the design. Petter left Westland to join the English Electric company in December 1944, in 1945, English Electric formalised its own in-house aircraft design team to pursuit this design. The Canberra had its origins in a 1944 requirement issued by the Air Ministry for a successor to the de Havilland Mosquito. This requirement, the initial revision being E. 3/45, sought a high altitude, further specification refinements were issued, including B. 3/45 and B. 5/47, issued further details such as a three-man crew and other features such as a visual bombing capability
41.
Oscillation
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Oscillation is the repetitive variation, typically in time, of some measure about a central value or between two or more different states. The term vibration is used to describe mechanical oscillation. Familiar examples of oscillation include a swinging pendulum and alternating current power, the simplest mechanical oscillating system is a weight attached to a linear spring subject to only weight and tension. Such a system may be approximated on an air table or ice surface, the system is in an equilibrium state when the spring is static. If the system is displaced from the equilibrium, there is a net restoring force on the mass, tending to bring it back to equilibrium. However, in moving the back to the equilibrium position, it has acquired momentum which keeps it moving beyond that position. If a constant force such as gravity is added to the system, the time taken for an oscillation to occur is often referred to as the oscillatory period. All real-world oscillator systems are thermodynamically irreversible and this means there are dissipative processes such as friction or electrical resistance which continually convert some of the energy stored in the oscillator into heat in the environment. Thus, oscillations tend to decay with time there is some net source of energy into the system. The simplest description of this process can be illustrated by oscillation decay of the harmonic oscillator. In addition, a system may be subject to some external force. In this case the oscillation is said to be driven, some systems can be excited by energy transfer from the environment. This transfer typically occurs where systems are embedded in some fluid flow, at sufficiently large displacements, the stiffness of the wing dominates to provide the restoring force that enables an oscillation. The harmonic oscillator and the systems it models have a degree of freedom. More complicated systems have more degrees of freedom, for two masses and three springs. In such cases, the behavior of each variable influences that of the others and this leads to a coupling of the oscillations of the individual degrees of freedom. For example, two pendulum clocks mounted on a wall will tend to synchronise. This phenomenon was first observed by Christiaan Huygens in 1665, more special cases are the coupled oscillators where energy alternates between two forms of oscillation
42.
Radio navigation
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Radio navigation or radionavigation is the application of radio frequencies to determine a position of an object on the Earth. Like radiolocation, it is a type of radiodetermination and these systems used some form of directional radio antenna to determine the location of a broadcast station on the ground. Conventional navigation techniques are used to take a radio fix. These were introduced prior to World War I, and remain in use today, the first system of radio navigation was the Radio Direction Finder, or RDF. By tuning in a station and then using a directional antenna. A second measurement using another station was then taken, using triangulation, the two directions can be plotted on a map where their intersection reveals the location of the navigator. Early RDF systems normally used an antenna, a small loop of metal wire that is mounted so it can be rotated around a vertical axis. By rotating the loop and looking for the angle of the null, loop antennas can be seen on most pre-1950s aircraft and ships. The main problem with RDF is that it required a special antenna on the vehicle, a smaller problem is that the accuracy of the system is based to a degree on the size of the antenna, but larger antennas would likewise make the installation more difficult. During the era between World War I and World War II, a number of systems were introduced that placed the antenna on the ground. Then they waited for the signal to either peak or disappear as the antenna pointed in their direction. By timing the delay between the signal and the peak/null, then dividing by the known rotational rate of the station. The first such system was the German Telefunken Kompass Sender, which operations in 1907 and was used operationally by the Zeppelin fleet until 1918. An improved version was introduced by the UK as the Orfordness Beacon in 1929, a number of improved versions followed, replacing the mechanical motion of the antennas with phasing techniques that produced the same output pattern with no moving parts. One of the longest lasting examples was Sonne, which went into operation just before World War II, the modern VOR system is based on the same principles. A great advance in the RDF technique was introduced in the form of phase comparisons of a signal as measured on two or more antennas, or a single highly directional solenoid. These receivers were dramatically smaller, more accurate, and simpler to operate and this also led to a revival in the operation of simple radio beacons for use with these RDF systems, now referred to as non-directional beacons. As the LF/MF signals used by NDBs can follow the curvature of earth, NDB can be categorized as long range or short range depending on their power
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Gee (navigation)
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Gee, sometimes written GEE, was a radio navigation system used by the Royal Air Force during World War II. It measured the time delay between two signals to produce a fix, with accuracy on the order of a few hundred metres at ranges up to about 350 miles. It was the first hyperbolic system to be used operationally. For large, fixed targets, like the cities that were attacked at night, jamming reduced its usefulness as a bombing aid, but it remained in use as a navigational aid in the UK area throughout the war. Gee remained an important part of the Royal Air Forces suite of systems in the post-war era, and was featured on aircraft such as the English Electric Canberra. It also saw use, and a number of new Gee chains were set up to support military. The system started to be shut down in the late 1960s, Gee also inspired the original LORAN system The basic idea of radio-based hyperbolic navigation was well known in the 1930s, but the equipment needed to build it was not widely available at the time. The main problem involved the determination of the difference in timing of two closely spaced signals, differences in milli- and micro-seconds. During the 1930s, the development of radar demanded devices that could measure these sorts of signal timings. In the case of Chain Home, transmission aerials sent out signals, an oscilloscope was used to measure the time between transmission and reception. The transmitter triggered a trace moving quickly along the oscilloscope display, Radar can also be used as a navigation system. If two stations are able to communicate, they could compare their measurements of the distance to a target and this calculation could then be sent to the aircraft by radio. This is a fairly manpower-intensive operation, and while it was used by both the British and Germans during the war, the workload meant it could only be used to guide single aircraft. In October 1937, Robert J. Dippy, working at Robert Watson-Watts radar laboratory at RAF Bawdsey and he envisaged two transmitting antennas positioned about 10 miles apart on either side of a runway. A transmitter midway between the two antennas would send a signal to both, which would ensure that both antennas would re-broadcast the signal at the same instant. A receiver in the aircraft would tune in these signals and send them to an A-scope type display, if the aircraft was properly lined up with the runway, both signals would be received at the same instant, and thus be drawn at the same point on the display. If the aircraft was located to one side or the other, one of the signals would be received before the other, forming two distinct peaks on the display. By determining which signal was being received first, pilots would know that they were closer to that antenna, watt liked the idea, but at the time there did not appear to be a pressing need for the system
