Nijmegen is a city in the Dutch province of Gelderland, on the Waal river close to the German border. Nijmegen is the oldest city in the Netherlands, the first to be recognized as such in Roman times, in 2005 celebrated 2,000 years of existence; the municipality is part of the Arnhem-Nijmegen urban region, a metropolitan area with 736,107 inhabitants in 2011. The municipality is formed by the city of Nijmegen, incorporating the former villages of Hatert and Neerbosch, as well as the urban expansion project of Waalsprong, situated north of the river Waal and including the village of Lent and the hamlet of't Zand, as well as the new suburbs of Nijmegen-Oosterhout and Nijmegen-Ressen; the city lies a few kilometers from the border with Germany, to some extent the westernmost villages in the municipality of Kranenburg, function as dormitories for people who work in the Dutch city of Nijmegen in part due to the immigration of Dutch people from the region who were attracted by the lower house pricing just across the border.
The German city of Duisburg is about 78 km away. The first mention of Nijmegen in history is in the 1st century BC, when the Romans built a military camp on the place where Nijmegen was to appear. By 69, when the Batavians, the original inhabitants of the Rhine and Maas delta, revolted, a village called Oppidum Batavorum had formed near the Roman camp; this village was destroyed in the revolt, but when it had ended the Romans built another, bigger camp where the Legio X Gemina was stationed. Soon after, another village formed around this camp. In 98, Nijmegen was the first of two settlements in what is now the Kingdom of the Netherlands to receive Roman city rights. In 103, the X Gemina was re-stationed to Vindobona, modern day Vienna, which may have been a major blow to the economy of the village around the camp, losing around 5000 inhabitants. In 104 Emperor Trajan renamed the town, which now became known as Ulpia Noviomagus Batavorum, Noviomagus for short. Beginning in the second half of the 4th century, Roman power decreased and Noviomagus became part of the Frankish kingdom.
It appeared around this time on the Peutinger Map. It has been contended that in the 8th century Emperor Charlemagne maintained his palatium in Nijmegen on at least four occasions. During his brief deposition of 830, the emperor Louis the Pious was sent to Nijmegen by his son Lothar I. Thanks to the Waal river, trade flourished; the powerful Henry VI, Holy Roman Emperor was born at Nijmegen in 1165. In 1230 his son Frederick II, Holy Roman Emperor granted Nijmegen city rights. In 1247, the city was ceded to the count of Guelders as collateral for a loan; the loan was never repaid, Nijmegen has been a part of Gelderland since. This did not hamper trade; the arts flourished in this period. Famous medieval painters like the Limbourg brothers were educated in Nijmegen; some of Hieronymus Bosch's ancestors came from the city. During the Dutch Revolt, trade came to a halt and though Nijmegen became a part of the Republic of United Provinces after its capture from the Spanish in 1591, it remained a border town and had to endure multiple sieges.
In 1678 Nijmegen was host to the negotiations between the European powers that aimed to put an end to the constant warfare that had ravaged the continent for years. The result was the Treaty of Nijmegen that failed to provide for a lasting peace. In the second half of the 19th century, the fortifications around the city became a major problem. There were too many inhabitants inside the walls, but the fortifications could not be demolished because Nijmegen was deemed as being of vital importance to the defence of the Netherlands; when events in the Franco-Prussian war proved that old-fashioned fortifications were no more of use, this policy was changed and the fortifications were dismantled in 1874. The old castle had been demolished in 1797, so that its bricks could be sold. Through the second half of the 19th century and the first half of the 20th century, Nijmegen grew steadily; the Waal was bridged in 1878 by a rail bridge and in 1936 by a car bridge, claimed to be Europe's biggest bridge at the time.
In 1923 the current Radboud University Nijmegen was founded and in 1927 a channel was dug between the Waal and Maas rivers. World War IIIn 1940, the Netherlands was invaded by Germany with Nijmegen being the first Dutch city to fall into German hands. On 22 February 1944, Nijmegen was bombed by American planes, causing great damage to the city centre, it was subsequently claimed by the Allies that the American pilots thought they were bombing the German city of Kleve, while the Germans alleged that it was a planned operation authorised by the Dutch government in exile. The Dutch organization for investigating wartime atrocities, the NIOD, announced in January 2005 that its study of the incident confirmed that it was an accident caused by poor communications and chaos in the airspace. Over 750 people died in the bombardment. During September 1944, the city saw heavy fighting during Operation Market Garden; the objective in Nijmegen was to prevent the Germans from destroying the bridges. Capturing the road bridge allowed the British Army XXX Corps to attempt to reach the 1st British Airborne Division in Arnhem.
The bridge was defended by over 300 German troops on both the north and south sides with close to 20 anti-tank guns and two anti-aircraft guns, supported with artillery. The
Automatic Packet Reporting System
Automatic Packet Reporting System is an amateur radio-based system for real time digital communications of information of immediate value in the local area. Data can include object Global Positioning System coordinates, weather station telemetry, text messages, announcements and other telemetry. APRS data can be displayed on a map, which can show stations, tracks of moving objects, weather stations and rescue data, direction finding data. APRS data are transmitted on a single shared frequency to be repeated locally by area relay stations for widespread local consumption. In addition, all such data are ingested into the APRS Internet System via an Internet-connected receiver and distributed globally for ubiquitous and immediate access. Data shared via radio or Internet are collected by all users and can be combined with external map data to build a shared live view. APRS has been developed since the late 1980s by Bob Bruninga, call sign WB4APR a senior research engineer at the United States Naval Academy.
He still maintains the main APRS Web site. The initialism "APRS" was derived from his call sign. Bob Bruninga, a senior research engineer at the United States Naval Academy, implemented the earliest ancestor of APRS on an Apple II computer in 1982; this early version was used to map high frequency Navy position reports. The first use of APRS was in 1984, when Bruninga developed a more advanced version on a Commodore VIC-20 for reporting the position and status of horses in a 100-mile endurance run. During the next two years, Bruninga continued to develop the system, which he now called the Connectionless Emergency Traffic System. Following a series of Federal Emergency Management Agency exercises using CETS, the system was ported to the IBM Personal Computer. During the early 1990s, CETS continued to evolve into its current form; as GPS technology became more available, "Position" was replaced with "Packet" to better describe the more generic capabilities of the system and to emphasize its uses beyond mere position reporting.
APRS, is a digital communications protocol for exchanging information among a large number of stations covering a large area referred to as "IP-ers". As a multi-user data network, it is quite different from conventional packet radio. Rather than using connected data streams where stations connect to each other and packets are acknowledged and retransmitted if lost, APRS operates in an unconnected broadcast fashion, using unnumbered AX.25 frames. APRS packets are transmitted for all other stations to use. Packet repeaters, called digipeaters, form the backbone of the APRS system, use store and forward technology to retransmit packets. All stations operate on the same radio channel, packets move through the network from digipeater to digipeater, propagating outward from their point of origin. All stations within radio range of each digipeater receive the packet. At each digipeater, the packet path is changed; the packet will only be repeated through a certain number of digipeaters — or hops — depending upon the all-important "PATH" setting.
Digipeaters keep track of the packets they forward for a period of time, thus preventing duplicate packets from being retransmitted. This keeps packets from circulating in endless loops inside the ad-hoc network. Most packets are heard by an APRS Internet Gateway, called an IGate, the packets are routed on to the Internet APRS backbone for display or analysis by other users connected to an APRS-IS server, or on a Web site designed for the purpose. While it would seem that using unconnected and unnumbered packets without acknowledgment and retransmission on a shared and sometimes congested channel would result in poor reliability due to a packet being lost, this is not the case, because the packets are transmitted to everyone and multiplied many times over by each digipeater; this means that all digipeaters and stations in range get a copy, proceed to broadcast it to all other digipeaters and stations within their range. The end result is. Therefore, packets can sometimes be heard some distance from the originating station.
Packets can be digipeated tens of kilometers or hundreds of kilometers, depending on the height and range of the digipeaters in the area. When a packet is transmitted, it is duplicated many times as it radiates out, taking all available paths until the number of "hops" allowed by the path setting is consumed. APRS contains a number of packet types, including position/object/item, messages, weather reports and telemetry; the position/object/item packets contain the latitude and longitude, a symbol to be displayed on the map, have many optional fields for altitude, speed, radiated power, antenna height above average terrain, antenna gain, voice operating frequency. Positions of fixed stations are configured in the APRS software. Moving stations automatically derive their position information from a GPS receiver connected to the APRS equipment; the map display uses these fields to plot communication range of all participants and facilitate the ability to contact users during both routine and emergency situations.
Each position/object/item packet can use any of several hundred different symbols. Position/objects/items can contain weather information or can be any number of dozens of standardised weather symbols; each symbol on an APRS map can display many attributes, discriminated either by colour or
Radar is a detection system that uses radio waves to determine the range, angle, or velocity of objects. It can be used to detect aircraft, spacecraft, guided missiles, motor vehicles, weather formations, terrain. A radar system consists of a transmitter producing electromagnetic waves in the radio or microwaves domain, a transmitting antenna, a receiving antenna and a receiver and processor to determine properties of the object. Radio waves from the transmitter reflect off the object and return to the receiver, giving information about the object's location and speed. Radar was developed secretly for military use by several nations in the period before and during World War II. A key development was the cavity magnetron in the UK, which allowed the creation of small systems with sub-meter resolution; the term RADAR was coined in 1940 by the United States Navy as an acronym for RAdio Detection And Ranging The term radar has since entered English and other languages as a common noun, losing all capitalization.
The modern uses of radar are diverse, including air and terrestrial traffic control, radar astronomy, air-defense systems, antimissile systems, marine radars to locate landmarks and other ships, aircraft anticollision systems, ocean surveillance systems, outer space surveillance and rendezvous systems, meteorological precipitation monitoring and flight control systems, guided missile target locating systems, ground-penetrating radar for geological observations, range-controlled radar for public health surveillance. High tech radar systems are associated with digital signal processing, machine learning and are capable of extracting useful information from high noise levels. Radar is a key technology that the self-driving systems are designed to use, along with sonar and other sensors. Other systems similar to radar make use of other parts of the electromagnetic spectrum. One example is "lidar". With the emergence of driverless vehicles, Radar is expected to assist the automated platform to monitor its environment, thus preventing unwanted incidents.
As early as 1886, German physicist Heinrich Hertz showed that radio waves could be reflected from solid objects. In 1895, Alexander Popov, a physics instructor at the Imperial Russian Navy school in Kronstadt, developed an apparatus using a coherer tube for detecting distant lightning strikes; 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, but he did nothing more with this observation; 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, but not its distance from the transmitter, he obtained a patent for his detection device in April 1904 and a patent for a related amendment for estimating the distance to the ship.
He got a British patent on September 23, 1904 for a full radar system, that he called a telemobiloscope. It operated on a 50 cm wavelength and the pulsed radar signal was created via a spark-gap, his system used the classic antenna setup of horn antenna with parabolic reflector and was presented to German military officials in practical tests in Cologne and Rotterdam harbour but was rejected. In 1915, Robert Watson-Watt used radio technology to provide advance warning to airmen and during the 1920s went on to lead the U. K. research establishment to make many advances using radio techniques, including the probing of the ionosphere and the detection of lightning at long distances. Through his lightning experiments, Watson-Watt became an expert on the use of radio direction finding before turning his inquiry to shortwave transmission. Requiring a suitable receiver for such studies, he told the "new boy" Arnold Frederic Wilkins to conduct an extensive review of available shortwave units. Wilkins would select a General Post Office model after noting its manual's description of a "fading" effect when aircraft flew overhead.
Across the Atlantic in 1922, after placing a transmitter and receiver on opposite sides of the Potomac River, U. S. Navy researchers A. Hoyt Taylor and Leo C. Young discovered that ships passing through the beam path caused the received signal to fade in and out. Taylor submitted a report, suggesting that this phenomenon might be used to detect the presence of ships in low visibility, but the Navy did not continue the work. Eight years Lawrence A. Hyland at the Naval Research Laboratory observed similar fading effects from passing aircraft. Before the Second World War, researchers in the United Kingdom, Germany, Japan, the Netherlands, the Soviet Union, the United States, independently and in great secrecy, developed technologies that led to the modern version of radar. Australia, New Zealand, South Africa followed prewar Great Britain's radar development, Hungary generated its radar technology during the war. In France in 1934, following systematic studies on the split-anode magnetron, the research branch of the Compagnie Générale de Télégraphie Sans Fil headed by Maurice Ponte with Henri Gutton, Sylvain Berline and M. Hugon, began developing an obstacle-locatin
India known as the Republic of India, is a country in South Asia. It is the seventh largest country by area and with more than 1.3 billion people, it is the second most populous country as well as the most populous democracy in the world. Bounded by the Indian Ocean on the south, the Arabian Sea on the southwest, the Bay of Bengal on the southeast, it shares land borders with Pakistan to the west. In the Indian Ocean, India is in the vicinity of Sri Lanka and the Maldives, while its Andaman and Nicobar Islands share a maritime border with Thailand and Indonesia; the Indian subcontinent was home to the urban Indus Valley Civilisation of the 3rd millennium BCE. In the following millennium, the oldest scriptures associated with Hinduism began to be composed. Social stratification, based on caste, emerged in the first millennium BCE, Buddhism and Jainism arose. Early political consolidations took place under the Gupta empires. In the medieval era, Zoroastrianism and Islam arrived, Sikhism emerged, all adding to the region's diverse culture.
Much of the north fell to the Delhi Sultanate. The economy expanded in the 17th century in the Mughal Empire. In the mid-18th century, the subcontinent came under British East India Company rule, in the mid-19th under British Crown rule. A nationalist movement emerged in the late 19th century, which under Mahatma Gandhi, was noted for nonviolent resistance and led to India's independence in 1947. In 2017, the Indian economy was the world's sixth largest by nominal GDP and third largest by purchasing power parity. Following market-based economic reforms in 1991, India became one of the fastest-growing major economies and is considered a newly industrialised country. However, it continues to face the challenges of poverty, corruption and inadequate public healthcare. A nuclear weapons state and regional power, it has the second largest standing army in the world and ranks fifth in military expenditure among nations. India is a federal republic governed under a parliamentary system and consists of 29 states and 7 union territories.
A pluralistic and multi-ethnic society, it is home to a diversity of wildlife in a variety of protected habitats. The name India is derived from Indus, which originates from the Old Persian word Hindush, equivalent to the Sanskrit word Sindhu, the historical local appellation for the Indus River; the ancient Greeks referred to the Indians as Indoi, which translates as "The people of the Indus". The geographical term Bharat, recognised by the Constitution of India as an official name for the country, is used by many Indian languages in its variations, it is a modernisation of the historical name Bharatavarsha, which traditionally referred to the Indian subcontinent and gained increasing currency from the mid-19th century as a native name for India. Hindustan is a Middle Persian name for India, it was introduced into India by the Mughals and used since then. Its meaning varied, referring to a region that encompassed northern India and Pakistan or India in its entirety; the name may refer to either the northern part of India or the entire country.
The earliest known human remains in South Asia date to about 30,000 years ago. Nearly contemporaneous human rock art sites have been found in many parts of the Indian subcontinent, including at the Bhimbetka rock shelters in Madhya Pradesh. After 6500 BCE, evidence for domestication of food crops and animals, construction of permanent structures, storage of agricultural surplus, appeared in Mehrgarh and other sites in what is now Balochistan; these developed into the Indus Valley Civilisation, the first urban culture in South Asia, which flourished during 2500–1900 BCE in what is now Pakistan and western India. Centred around cities such as Mohenjo-daro, Harappa and Kalibangan, relying on varied forms of subsistence, the civilization engaged robustly in crafts production and wide-ranging trade. During the period 2000–500 BCE, many regions of the subcontinent transitioned from the Chalcolithic cultures to the Iron Age ones; the Vedas, the oldest scriptures associated with Hinduism, were composed during this period, historians have analysed these to posit a Vedic culture in the Punjab region and the upper Gangetic Plain.
Most historians consider this period to have encompassed several waves of Indo-Aryan migration into the subcontinent from the north-west. The caste system, which created a hierarchy of priests and free peasants, but which excluded indigenous peoples by labeling their occupations impure, arose during this period. On the Deccan Plateau, archaeological evidence from this period suggests the existence of a chiefdom stage of political organisation. In South India, a progression to sedentary life is indicated by the large number of megalithic monuments dating from this period, as well as by nearby traces of agriculture, irrigation tanks, craft traditions. In the late Vedic period, around the 6th century BCE, the small states and chiefdoms of the Ganges Plain and the north-western regions had consolidated into 16 major oligarchies and monarchies that were known as the mahajanapadas; the emerging urbanisation gave rise to non-Vedic religious movements, two of which became independent religions. Jainism came into prominence during the life of Mahavira.
Buddhism, based on the teachings of Gautama Buddha, attracted followers from all social classes excepting the middle
Very high frequency
High frequency is the ITU designation for the range of radio frequency electromagnetic waves from 30 to 300 megahertz, with corresponding wavelengths of ten meters to one meter. Frequencies below VHF are denoted high frequency, the next higher frequencies are known as ultra high frequency. Common uses for radio waves in the VHF band are FM radio broadcasting, television broadcasting, two way land mobile radio systems, long range data communication up to several tens of kilometers with radio modems, amateur radio, marine communications. Air traffic control communications and air navigation systems work at distances of 100 kilometres or more to aircraft at cruising altitude. In the Americas and many other parts of the world, VHF Band I was used for the transmission of analog television; as part of the worldwide transition to digital terrestrial television most countries require broadcasters to air television in the VHF range using digital rather than analog format. Radio waves in the VHF band propagate by line-of-sight and ground-bounce paths.
They do not follow the contour of the Earth as ground waves and so are blocked by hills and mountains, although because they are weakly refracted by the atmosphere they can travel somewhat beyond the visual horizon out to about 160 km. They can penetrate building walls and be received indoors, although in urban areas reflections from buildings cause multipath propagation, which can interfere with television reception. Atmospheric radio noise and interference from electrical equipment is less of a problem in the band than at lower frequencies; the VHF band is the first band at which efficient transmitting antennas are small enough that they can be mounted on vehicles and portable devices, so the band is used for two-way land mobile radio systems, such as walkie-talkies, two way radio communication with aircraft and ships. When conditions are right, VHF waves can travel long distances by tropospheric ducting due to refraction by temperature gradients in the atmosphere. For analog TV, VHF transmission range is a function of transmitter power, receiver sensitivity, distance to the horizon, since VHF signals propagate under normal conditions as a near line-of-sight phenomenon.
The distance to the radio horizon is extended over the geometric line of sight to the horizon, as radio waves are weakly bent back toward the Earth by the atmosphere. An approximation to calculate the line-of-sight horizon distance is: distance in nautical miles = 1.23 × A f where A f is the height of the antenna in feet distance in kilometers = 12.746 × A m where A m is the height of the antenna in meters. These approximations are only valid for antennas at heights that are small compared to the radius of the Earth, they may not be accurate in mountainous areas, since the landscape may not be transparent enough for radio waves. In engineered communications systems, more complex calculations are required to assess the probable coverage area of a proposed transmitter station; the accuracy of these calculations for digital TV signals is being debated. VHF is the first band at which wavelengths are small enough that efficient transmitting antennas are short enough to mount on vehicles and handheld devices, a quarter wave whip antenna at VHF frequencies is 25 cm to 2.5 meter long.
So the VHF and UHF wavelengths are used for two-way radios in vehicles and handheld transceivers and walkie-talkies. Portable radios use whips or rubber ducky antennas, while base stations use larger fiberglass whips or collinear arrays of vertical dipoles. For directional antennas, the Yagi antenna is the most used as a high gain or "beam" antenna. For television reception, the Yagi is used, as well as the log-periodic antenna due to its wider bandwidth. Helical and turnstile antennas are used for satellite communication since they employ circular polarization. For higher gain, multiple Yagis or helicals can be mounted together to make array antennas. Vertical collinear arrays of dipoles can be used to make high gain omnidirectional antennas, in which more of the antenna's power is radiated in horizontal directions. Television and FM broadcasting stations use collinear arrays of specialized dipole antennas such as batwing antennas. Certain subparts of the VHF band have the same use around the world.
Some national uses are detailed below. 50–54 MHz: Amateur Radio 6-meter band. 108–118 MHz: Air navigation beacons VOR and Instrument Landing System localizer. 118–137 MHz: Airband for air traffic control, AM, 121.5 MHz is emergency frequency 144–148 MHz: Amateur Radio 2-meter band. The VHF TV band in Australia was allocated channels 1 to 10-with channels 2, 7 and 9 assigned for the initial services in Sydney and Melbourne, the same channels were assigned in Brisbane and Perth. Other capital cities and regional areas used a combination of these and other frequencies as available; the initial commercial services in Hobart and Darwin were allocated channels 6 and 8 rather than 7 or 9. By the early 1960s it became apparent that the 10 VHF channels were insufficient to support the growth of television services; this was rectified by the addition of th
Automatic identification system
The automatic identification system is an automatic tracking system that uses transponders on ships and is used by vessel traffic services. When satellites are used to detect AIS signatures, the term Satellite-AIS is used. AIS information supplements marine radar, which continues to be the primary method of collision avoidance for water transport. Information provided by AIS equipment, such as unique identification, position and speed, can be displayed on a screen or an ECDIS. AIS is intended to assist a vessel's watchstanding officers and allow maritime authorities to track and monitor vessel movements. AIS integrates a standardized VHF transceiver with a positioning system such as a GPS receiver, with other electronic navigation sensors, such as a gyrocompass or rate of turn indicator. Vessels fitted with AIS transceivers can be tracked by AIS base stations located along coast lines or, when out of range of terrestrial networks, through a growing number of satellites that are fitted with special AIS receivers which are capable of deconflicting a large number of signatures.
The International Maritime Organization's International Convention for the Safety of Life at Sea requires AIS to be fitted aboard international voyaging ships with 300 or more gross tonnage, all passenger ships regardless of size. For a variety of reasons, ships can turn off their AIS transponders. AIS is intended to allow ships to view marine traffic in their area and to be seen by that traffic; this requires a dedicated VHF AIS transceiver that allows local traffic to be viewed on an AIS enabled chartplotter or computer monitor while transmitting information about the ship itself to other AIS receivers. Port authorities or other shore-based facilities may be equipped with receivers only, so that they can view the local traffic without the need to transmit their own location. All AIS transceivers equipped traffic can be viewed this way reliably but is limited to the VHF range, about 10–20 nautical miles. If a suitable chartplotter is not available, local area AIS transceiver signals may be viewed via a computer using one of several computer applications such as ShipPlotter and Gnuais.
These demodulate the signal from a modified marine VHF radiotelephone tuned to the AIS frequencies and convert into a digital format that the computer can read and display on a monitor. Because computer AIS monitoring applications and normal VHF radio transceivers do not possess AIS transceivers, they may be used by shore-based facilities that have no need to transmit or as an inexpensive alternative to a dedicated AIS device for smaller vessels to view local traffic but, of course, the user will remain unseen by other traffic on the network. A secondary and emerging use for AIS data is to make it viewable publicly, on the internet, without the need for an AIS receiver. Global AIS transceiver data collected from both satellite and internet-connected shore-based stations are aggregated and made available on the internet through a number of service providers. Data aggregated this way can be viewed on any internet-capable device to provide near global, real-time position data from anywhere in the world.
Typical data includes vessel name, location and heading on a map, is searchable, has unlimited, global range and the history is archived. Most of this data is free of charge but satellite data and special services such as searching the archives are supplied at a cost; the data is a read-only view and the users will not be seen on the AIS network itself. Shore-based AIS receivers contributing to the internet are run by a large number of volunteers. AIS mobile apps are readily available for use with Android, Windows and iOS devices. See External links below for a list of internet-based AIS service providers. Ship owners and cargo dispatchers use these services to find and track vessels and their cargoes while marine enthusiasts may add to their photograph collections; the 2002 IMO SOLAS Agreement included a mandate that required most vessels over 300GT on international voyages to fit a Class A type AIS transceiver. This was the first mandate for the use of AIS equipment and affected 100,000 vessels.
In 2006, the AIS standards committee published the Class B type AIS transceiver specification, designed to enable a simpler and lower-cost AIS device. Low-cost Class B transceivers became available in the same year triggering mandate adoptions by numerous countries and making large-scale installation of AIS devices on vessels of all sizes commercially viable. Since 2006, the AIS technical standard committees have continued to evolve the AIS standard and product types to cover a wide range of applications from the largest vessel to small fishing vessels and life boats. In parallel and authorities have instigated projects to fit varying classes of vessels with an AIS device to improve safety and security. Most mandates are focused with leisure vessels selectively choosing to fit. In 2010 most commercial vessels operating on the European Inland Waterways were required to fit an Inland waterway certified Class A, all EU fishing boats over 15m will have to have a Class A by May 2014, the US has a long-pending extension to their existing AIS fit rules, expected to come into force during 2013.
It is estimated that as of 2012, some 250,000 vessels have fitted an AIS transceiver of some type, with a further 1 million required to do so in the near future and larger projects under consideration. AIS was developed in the 1990s as a high intensity, short-range identification and tracking network
Air traffic control
Air traffic control is a service provided by ground-based air traffic controllers who direct aircraft on the ground and through controlled airspace, can provide advisory services to aircraft in non-controlled airspace. The primary purpose of ATC worldwide is to prevent collisions and expedite the flow of air traffic, provide information and other support for pilots. In some countries, ATC is operated by the military. 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 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 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; the pilot in command is the final authority for the safe operation of the aircraft and may, in an emergency, deviate from ATC instructions to the extent required to maintain safe operation of their aircraft.
Pursuant to requirements of the International Civil Aviation Organization, ATC operations are conducted either in the English language or the language used by the station on the ground. In practice, the native language for a region is used. In 1920, Croydon Airport, London was the first airport in the world to introduce 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 and track the movements of reconnaissance aircraft. Over time, the AMRS morphed into flight service stations. Today's flight service stations do not issue control instructions, but provide pilots with many other flight related informational services, they do relay control instructions from ATC in areas where flight service is the only facility with radio or phone coverage. The first airport traffic control tower, regulating arrivals and surface movement of aircraft at a specific airport, opened in Cleveland in 1930.
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 route 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 and Cleveland; the primary method of controlling the immediate airport environment is visual observation from the airport control tower. The tower is a windowed structure located on the airport grounds. Air traffic controllers are responsible for the separation and efficient movement of aircraft and vehicles operating on the taxiways and runways of the airport itself, aircraft in the air near the airport 5 to 10 nautical miles depending on the airport procedures. Surveillance displays are available to controllers at larger airports to assist with controlling air traffic. Controllers may use a radar system called secondary surveillance radar for airborne traffic approaching and departing.
These displays include a map of the area, the position of various aircraft, data tags that include aircraft identification, speed and other information described in local procedures. In adverse weather conditions the tower controllers may use surface movement radar, surface movement guidance and control systems or advanced SMGCS to control traffic on the manoeuvring area; the areas of responsibility for tower controllers fall into three general operational disciplines: local control or air control, ground control, flight data / clearance delivery—other categories, such as Apron control or ground movement planner, may exist at busy airports. While each tower may have unique airport-specific procedures, such as multiple teams of controllers at major or complex airports with multiple runways, the following provides a general concept of the delegation of responsibilities within the tower environment. 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.
Displays for the air traffic controllers may be live video, synthetic images based on surveillance sensor data, or both. Ground control is responsible for the airport "movement" areas, as well as areas not released to the airlines or other users; this includes all taxiways, inactive runways, holding areas, some transitional aprons or intersections where aircraft arrive, having vacated the runway or departure gate. Exact areas and control responsibilities are defined in local documents and agreements at each airport. Any aircraft, vehicle, or person walking or working in these areas is required to have clearance from ground control; this is done via VHF/UHF radio, but there may be special cases where other procedures are used. Aircraft or vehicles without radios must respond to ATC instructions via aviation light signals or else be led by vehicles with radios. People working on the airport surface have a communications link through which they can communicate with ground control either by handheld radio or cell phone.
Ground control is vital to the smooth operation of the airport, because this position impacts th