Precession is a change in the orientation of the rotational axis of a rotating body. In an appropriate reference frame it can be defined as a change in the first Euler angle, whereas the third Euler angle defines the rotation itself. In other words, if the axis of rotation of a body is itself rotating about a second axis, that body is said to be precessing about the second axis. A motion in which the second Euler angle changes is called nutation. In physics, there are two types of precession: torque-induced. In astronomy, precession refers to any of several slow changes in an astronomical body's rotational or orbital parameters. An important example is the steady change in the orientation of the axis of rotation of the Earth, known as the precession of the equinoxes. Torque-free precession implies. In torque-free precession, the angular momentum is a constant, but the angular velocity vector changes orientation with time. What makes this possible is a time-varying moment of inertia, or more a time-varying inertia matrix.
The inertia matrix is composed of the moments of inertia of a body calculated with respect to separate coordinate axes. If an object is asymmetric about its principal axis of rotation, the moment of inertia with respect to each coordinate direction will change with time, while preserving angular momentum; the result is that the component of the angular velocities of the body about each axis will vary inversely with each axis' moment of inertia. The torque-free precession rate of an object with an axis of symmetry, such as a disk, spinning about an axis not aligned with that axis of symmetry can be calculated as follows: ω p = I s ω s I p cos where ωp is the precession rate, ωs is the spin rate about the axis of symmetry, Is is the moment of inertia about the axis of symmetry, Ip is moment of inertia about either of the other two equal perpendicular principal axes, α is the angle between the moment of inertia direction and the symmetry axis; when an object is not solid, internal vortices will tend to damp torque-free precession, the rotation axis will align itself with one of the inertia axes of the body.
For a generic solid object without any axis of symmetry, the evolution of the object's orientation, represented by a rotation matrix R that transforms internal to external coordinates, may be numerically simulated. Given the object's fixed internal moment of inertia tensor I0 and fixed external angular momentum L, the instantaneous angular velocity is ω = R I 0 − 1 R T L Precession occurs by recalculating ω and applying a small rotation vector ω dt for the short time dt; the errors induced by finite time steps tend to increase the rotational kinetic energy: E = ω ⋅ L 2 this unphysical tendency can be counteracted by applying a small rotation vector v perpendicular to both ω and L, noting that E ≈ E + ⋅ v Another type of torque-free precession can occur when there are multiple reference frames at work. For example, Earth is subject to local torque induced precession due to the gravity of the sun and moon acting on Earth's axis, but at the same time the solar system is moving around the galactic center.
As a consequence, an accurate measurement of Earth's axial reorientation relative to objects outside the frame of the moving galaxy must account for a minor amount of non-local torque-free precession, due to the solar system's motion. Torque-induced precession is the phenomenon in which the axis of a spinning object des
Low Earth orbit
A Low Earth Orbit is an Earth-centered orbit with an altitude of 2,000 km or less, or with at least 11.25 periods per day and an eccentricity less than 0.25. Most of the manmade objects in space are in LEO. A histogram of the mean motion of the cataloged objects shows that the number of objects drops beyond 11.25. There is a large variety of other sources; the altitude of an object in an elliptic orbit can vary along the orbit. For circular orbits, the altitude above ground can vary by as much as 30 km due to the oblateness of Earth's spheroid figure and local topography. While definitions in terms of altitude are inherently ambiguous, most of them fall within the range specified by an orbit period of 128 minutes because, according to Kepler's third law, this corresponds to a semi-major axis of 8,413 km. For circular orbits, this in turn corresponds to an altitude of 2,042 km above the mean radius of Earth, consistent with some of the upper limits in the LEO definitions in terms of altitude; the LEO region is defined by some sources as the region in space.
Some elliptical orbits may pass through the LEO region near their lowest altitude but are not in an LEO Orbit because their highest altitude exceeds 2,000 km. Sub-orbital objects can reach the LEO region but are not in an LEO orbit because they re-enter the atmosphere; the distinction between LEO orbits and the LEO region is important for analysis of possible collisions between objects which may not themselves be in LEO but could collide with satellites or debris in LEO orbits. The International Space Station conducts operations in LEO. All crewed space stations to date, as well as the majority of satellites, have been in LEO; the altitude record for human spaceflights in LEO was Gemini 11 with an apogee of 1,374.1 km. Apollo 8 was the first mission to carry humans beyond LEO on December 21–27, 1968; the Apollo program continued during the four-year period spanning 1968 through 1972 with 24 astronauts who flew lunar flights but since there have been no human spaceflights beyond LEO. The mean orbital velocity needed to maintain a stable low Earth orbit is about 7.8 km/s, but reduces with increased orbital altitude.
Calculated for circular orbit of 200 km it is 7.79 km/s and for 1500 km it is 7.12 km/s. The delta-v needed to achieve low Earth orbit starts around 9.4 km/s. Atmospheric and gravity drag associated with launch adds 1.3–1.8 km/s to the launch vehicle delta-v required to reach normal LEO orbital velocity of around 7.8 km/s. The pull of gravity in LEO is only less than on the earth's surface; this is. However, an object in orbit is, in free fall, since there is no force holding it up; as a result objects in orbit, including people, experience a sense of weightlessness though they are not without weight. Objects in LEO encounter atmospheric drag from gases in the thermosphere or exosphere, depending on orbit height. Due to atmospheric drag, satellites do not orbit below 300 km. Objects in LEO orbit Earth between the denser part of the atmosphere and below the inner Van Allen radiation belt. Equatorial low Earth orbits are a subset of LEO; these orbits, with low inclination to the Equator, allow rapid revisit times and have the lowest delta-v requirement of any orbit.
Orbits with a high inclination angle to the equator are called polar orbits. Higher orbits include medium Earth orbit, sometimes called intermediate circular orbit, further above, geostationary orbit. Orbits higher than low orbit can lead to early failure of electronic components due to intense radiation and charge accumulation. In 2017, a very-low LEO orbit began to be seen in regulatory filings; this orbit, referred to as "VLEO", requires the use of novel technologies for orbit raising because they operate in orbits that would ordinarily decay too soon to be economically useful. A low Earth orbit requires the lowest amount of energy for satellite placement, it provides low communication latency. Satellites and space stations in LEO are more accessible for servicing. Since it requires less energy to place a satellite into a LEO, a satellite there needs less powerful amplifiers for successful transmission, LEO is used for many communication applications, such as the Iridium phone system; some communication satellites use much higher geostationary orbits, move at the same angular velocity as the Earth as to appear stationary above one location on the planet.
Satellites in LEO have a small momentary field of view, only able to observe and communicate with a fraction of the Earth at a time, meaning a network of satellites is required to in order to provide continuous coverage. Satellites in lower regions of LEO suffer from fast orbital decay, requiring either periodic reboosting to maintain a stable orbit, or launching replacement satellites when old ones re-enter. Earth observation satellites and spy satellites use LEO as they are able to see the surface of the Earth by being close to it, they are able to traverse the surface of the Earth. A majority of artificial satellites are placed in LEO, making one complete revolution around the Earth in about 90 minutes; the International Space Station is in a LEO about 330 km to 420 km above Earth's surfac
Cloud cover refers to the fraction of the sky obscured by clouds when observed from a particular location. Okta is the usual unit of measurement of the cloud cover; the cloud cover is correlated to the sunshine duration as the least cloudy locales are the sunniest ones while the cloudiest areas are the least sunny places. The global cloud cover averages around 0.68 when analyzing clouds with optical depth larger than 0.1. This value is lower when considering clouds with an optical depth larger than 2, higher when counting subvisible cirrus clouds. Clouds play multiple critical roles in the climate system. In particular, being bright objects in the visible part of the solar spectrum, they efficiently reflect light to space and thus contribute to the cooling of the planet. Cloud cover thus plays an important role in the energetic balance of the atmosphere and a variation of it is a consequence of and to the climate change expected by recent studies. Cloud cover values only vary by 0.03 from year to year, whereas the local, day to day variability in cloud amount rises to 0.3 over the globe.
Most data sets agree on the fact. Lastly, there is a latitudinal variation in the cloud cover, such that around 20°N there are regions with 0.10 less cloudiness than the global mean. The same variation is found 20°S. On the other hand, in the storm regions of the Southern Hemisphere midlatitudes were found to have with 0.15-0.25 more cloudiness than the global mean at 60°S. On average, about 52% of Earth is cloud-covered at any moment; some regions are always cloudy such as the Amazon Rainforest and some others are always clear such as the Sahara Desert. McIntosh, D. H. Meteorological Glossary, Her Majesty's Stationery Office, Met. O. 842, A. P. 897, 319 p. NSDL.arm.gov, Glossary of Atmospheric Terms, From the National Science Digital Library's Atmospheric Visualization Collection. Earthobersvatory.nasa.gov, Monthly maps of global cloud cover from NASA's Earth Observatory International Satellite Cloud Climatology Project, NASA's data products on their satellite observations NASA composite satellite image
STS-68 was a human spaceflight mission using Space Shuttle Endeavour that launched from Kennedy Space Center, Florida on 30 September 1994. Launch 30 September 1994 at 7:16:00.068 am EDT from Kennedy Space Center Launch Pad 39-A. The Launch window opened at 7:16 am EDT with a 2-hour-30-minute window. Orbiter mass at liftoff was 247,129 pounds including payload. Total vehicle mass was 2,045,879 kilograms. Payload liftoff mass 12,511 kilograms. Main Engine Cutoff was at an apogee of 115 nautical miles and a perigee of 28 nmi at MET of 8 min 35 s with Endeavour traveling at 25,779 ft/s. No OMS-1 burn. OMS-2 burn was 1 min 42 s at MET 33 min; the launch was scheduled 18 August 1994, but there was an RSLS abort at T-1.9 s after all three main engines ignited - the fifth time in the shuttle program where an RSLS abort occurred after main engine ignition. Previous aborts occurred on STS-41-D, STS-51-F, STS-55 and STS-51; the automatic abort was initiated by the onboard General Purpose Computers when the discharge temperature on MPS Main Engine #3 High Pressure Oxidizer Turbopump exceeded its redline value.
The HPOT operates at 28,120 rpm and boosts the liquid oxygen pressure from 422 to 4,300 psi. There are 2 sensor channels measuring temperature on the HPOT; the B channel indicated a redline condition. The temperature at shutdown was at 1563 degrees Rankine, while a normal HPOT discharge temperature is around 1,403 °R; the redline limit to initiate a shutdown is at 867 K. This limit increases to 980 K at T−1.3 s. Main Engine #3 has been used on two previous flights with 2,412 seconds of hot-fire time and a total of eight starts; this was the first flight for the HPOT on Main Engine #3. A new launch date was set for early October and moved up to late September; the procedure, used on previous aborts treats an RSLS abort after SSME ignition as a launch and to require a complete engine reinspection. A rollback of Endeavour to the VAB was done on 24 August 1994. Afterwards, Endeavour's SSMEs were removed and inspected. Three flight certified SSMEs were installed on the orbiter and Endeavour was rolled back to the launch pad on 13 September 1994.
SSME #3 was shipped to the Stennis Space Center in Mississippi for test stand firing over the Labor day weekend. Transatlantic Abort Landing sites for the initial launch attempt were Zaragoza, Moron and Ben Guerir, Morocco. Abort Once Around landing site was White Sands Space Harbor, New Mexico, USA. Landing 11 October 1994, 1:02:09 pm EDT. Edwards Air Force Base concrete Runway 22. Endeavour did an OMS deorbit burn at 12:09 pm EDT about 4,600 miles from the landing strip at Edwards Air Force Base; the burn lasted 2 min 17 s. Astronaut John Casper flew the shuttle training aircraft at Edwards and said the weather was clear with light winds. Approach was from the southwest with a right overhead turn of 280 degrees. Nose wheel touchdown at 13:02:21 EDT. Wheel stop at 13:03:08 EDT. Rollout was 8,495 feet down the runway. Landing speed at main touchdown was 265 mph. Orbiter landing mass was 100,709 kilograms. Payload landing mass was 12,511 kilograms. Landing was scheduled for KSC, 11 October 1994 at 11:36 am EDT.
The KSC landing attempts on that date were waved off due to cloud cover over the Shuttle Landing Facility. On Friday, 30 September 1994 at 9 am CST, STS-68 MCC Status Report #1 reports: The Flight Control team in Houston gave the "Go for Orbit Operations" just before 8 am The crew began setting up the experiment and systems hardware aboard Endeavour; the primary payload on this flight is the Space Radar Laboratory, making its second flight to study the Earth's environment. Experiment operations will be conducted around the clock on this flight, with the astronauts divided into two teams. Commander Michael A. Baker, pilot Terrence W. Wilcutt and mission specialist Peter J. K. Wisoff are the "red team". Mission specialists Daniel W. Bursch, Thomas D. Jones and Steven L. Smith are the "blue team". On Friday, 30 September 1994 at 5 pm CDT, STS-68 MCC Status Report # 2 reports: Shortly after 4 pm that day, flight controllers reported that the on-orbit checkout of the Spaceborne Imaging Radar-C and the Synthetic Aperture Radar had been completed, that the primary SRL-2 instruments were ready for operation.
Throughout the checkout, data takes were recorded over a number including Raco, Michigan. In addition to the prime payload, Wilcutt activated the Commercial Protein Crystal Growth Experiment, the Cosmic Radiation Effects and Activation Monitor, checked on the mouse-ear cress seedlings growing in the CHROMEX-05 experiment; the crew engineered an in-flight maintenance procedure to get additional cooling air to the CPCG apparatus after higher than desired temperatures were noted by crystal growth sensors. On Saturday, 1 October 1994 at 9 am CDT, STS-68 MCC Status Report # 3 reports: Environmental studies continued throughout Saturday morning aboard Endeavour as six astronauts working around the clock in two shifts assisted the Space Radar Laboratory science team on the ground with real-time observations from space. While Commander Mike Baker and Pilot Terry Wilcutt made attitude adjustments of the orbiter to assist in precisely
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
STS-41-G was the 13th flight of NASA's Space Shuttle program and the sixth flight of Space Shuttle Challenger. Challenger launched on 5 October 1984, conducted the second shuttle landing at Kennedy Space Center on 13 October, it was the first shuttle mission to carry a crew of seven, including the first crew with two women, the first American EVA involving a woman, the first Australian-born person to journey into space and the first astronaut with a beard and the first Canadian astronaut. STS-41-G was the third shuttle mission to carry an IMAX camera on board to document the flight. Film footage from the mission appeared. Leestma and Sullivan – EVA 1 EVA 1 Start: 11 October 1984 EVA 1 End: 11 October 1984 Duration: 3 hours, 29 minutes On 5 October 1984, Challenger launched from the Kennedy Space Center at 7:03 am EDT, marking the start of the STS-41-G mission. On board were seven crew members – the largest flight crew to fly on a single spacecraft at that time, they included commander Robert L. Crippen, making his fourth Shuttle flight and second in six months.
Leestma, Sally K. Ride and Kathryn D. Sullivan – and two payload specialists, Paul Scully-Power and Marc Garneau, the first Canadian citizen to serve as a Shuttle crew member, as well as the first Canadian in space; the mission marked the first time two female astronauts had flown together. Sullivan became the first American woman to walk in space when she and Leestma performed a 3-hour EVA on 11 October, demonstrating the Orbital Refueling System and proving the feasibility of refueling satellites in orbit. Nine hours after liftoff, the 5,087 pounds Earth Radiation Budget Satellite was deployed from the payload bay by the RMS robot arm, its on-board thrusters boosted it into orbit 350 miles above the Earth. ERBS was the first of three planned satellites designed to measure the amount of energy received from the Sun and reradiated into space, it studied the seasonal movement of energy from the tropics to the polar regions. Another major mission activity was the operation of the Shuttle Imaging Radar-B.
The SIR-B was part of the OSTA-3 experiment package in the payload bay, which included the Large Format Camera to photograph the Earth, another camera called MAPS which measured air pollution, a feature identification and location experiment called FILE, which consisted of two TV cameras and two 70 mm still cameras. The SIR-B was an improved version of a similar device flown on the OSTA-1 package during STS-2, it had an eight-panel antenna array measuring 35 feet by 7 feet. It operated throughout the flight, but problems were encountered with Challenger’s Ku band antenna, therefore much of the data had to be recorded on board the orbiter rather than transmitted to Earth in real-time as was planned. Payload Specialist Scully-Power, an employee of the U. S. Naval Research Lab, performed a series of oceanography observations during the mission. Garneau conducted a series of experiments sponsored by the Canadian government, called CANEX, which were related to medical, climatic and robotic science.
A number of GAS canisters, covering a wide variety of materials testing and physics experiments, were flown. A claim was made that the Soviet Terra-3 laser testing center was used to track Challenger with a low-power laser on 10 October; this caused the malfunction of on-board equipment and the temporary blinding of the crew, leading to a U. S. diplomatic protest. However, this story has been comprehensively denied by the crew members. During the 8-day, 5-hour, 23-minute, 33-second mission, Challenger traveled 3,289,444 miles and completed 132 orbits, it landed at the Shuttle Landing Facility at Kennedy Space Center – becoming the second shuttle mission to land there – on 13 October 1984, at 12:26 pm EDT. The STS-41-G mission was described in detail in the book Oceans to Orbit: The Story of Australia's First Man in Space, Paul Scully-Power by space historian Colin Burgess; the thirteen complete stars in the blue field of the U. S. flag of the mission insignia symbolize the flight's numerical designation in the Space Transportation System's mission sequence.
Gender symbols are placed next to each astronaut's name, a Canadian flag icon is placed next to Garneau's name. NASA began a tradition of playing music to astronauts during the Gemini program, first used music to wake up a flight crew during Apollo 15; each track is specially chosen by the astronauts' families, has a special meaning to an individual member of the crew, or is applicable to their daily activities. List of human spaceflights List of Space Shuttle missions This article incorporates public domain material from websites or documents of the National Aeronautics and Space Administration. Cooper, Henry S. F. Jr. Before Lift-off: The Making of a Space Shuttle Crew, Johns Hopkins University Press 1987 NASA mission summary STS-41-G Video Highlights The Dream is Alive IMAX film with footage from STS-41-G STS-41-G NST Program Mission Report
Remote sensing is the acquisition of information about an object or phenomenon without making physical contact with the object and thus in contrast to on-site observation the Earth. Remote sensing is used in numerous fields, including geography, land surveying and most Earth Science disciplines. In current usage, the term "remote sensing" refers to the use of satellite- or aircraft-based sensor technologies to detect and classify objects on Earth, including on the surface and in the atmosphere and oceans, based on propagated signals, it may be split into "passive" remote sensing. Passive sensors gather radiation, emitted or reflected by the object or surrounding areas. Reflected sunlight is the most common source of radiation measured by passive sensors. Examples of passive remote sensors include film photography, charge-coupled devices, radiometers. Active collection, on the other hand, emits energy in order to scan objects and areas whereupon a sensor detects and measures the radiation, reflected or backscattered from the target.
RADAR and LiDAR are examples of active remote sensing where the time delay between emission and return is measured, establishing the location and direction of an object. Remote sensing makes it possible to collect data of inaccessible areas. Remote sensing applications include monitoring deforestation in areas such as the Amazon Basin, glacial features in Arctic and Antarctic regions, depth sounding of coastal and ocean depths. Military collection during the Cold War made use of stand-off collection of data about dangerous border areas. Remote sensing replaces costly and slow data collection on the ground, ensuring in the process that areas or objects are not disturbed. Orbital platforms collect and transmit data from different parts of the electromagnetic spectrum, which in conjunction with larger scale aerial or ground-based sensing and analysis, provides researchers with enough information to monitor trends such as El Niño and other natural long and short term phenomena. Other uses include different areas of the earth sciences such as natural resource management, agricultural fields such as land usage and conservation, national security and overhead, ground-based and stand-off collection on border areas.
The basis for multispectral collection and analysis is that of examined areas or objects that reflect or emit radiation that stand out from surrounding areas. For a summary of major remote sensing satellite systems see the overview table. Conventional radar is associated with aerial traffic control, early warning, certain large scale meteorological data. Doppler radar is used by local law enforcements’ monitoring of speed limits and in enhanced meteorological collection such as wind speed and direction within weather systems in addition to precipitation location and intensity. Other types of active collection includes plasmas in the ionosphere. Interferometric synthetic aperture radar is used to produce precise digital elevation models of large scale terrain. Laser and radar altimeters on satellites have provided a wide range of data. By measuring the bulges of water caused by gravity, they map features on the seafloor to a resolution of a mile or so. By measuring the height and wavelength of ocean waves, the altimeters measure wind speeds and direction, surface ocean currents and directions.
Ultrasound and radar tide gauges measure sea level and wave direction in coastal and offshore tide gauges. Light detection and ranging is well known in examples of weapon ranging, laser illuminated homing of projectiles. LIDAR is used to detect and measure the concentration of various chemicals in the atmosphere, while airborne LIDAR can be used to measure heights of objects and features on the ground more than with radar technology. Vegetation remote sensing is a principal application of LIDAR. Radiometers and photometers are the most common instrument in use, collecting reflected and emitted radiation in a wide range of frequencies; the most common are visible and infrared sensors, followed by microwave, gamma ray and ultraviolet. They may be used to detect the emission spectra of various chemicals, providing data on chemical concentrations in the atmosphere. Spectropolarimetric Imaging has been reported to be useful for target tracking purposes by researchers at the U. S. Army Research Laboratory.
They determined that manmade items possess polarimetric signatures that are not found in natural objects. These conclusions were drawn from the imaging of military trucks, like the Humvee, trailers with their acousto-optic tunable filter dual hyperspectral and spectropolarimetric VNIR Spectropolarimetric Imager. Stereographic pairs of aerial photographs have been used to make topographic maps by imagery and terrain analysts in trafficability and highway departments for potential routes, in addition to modelling terrestrial habitat features. Simultaneous multi-spectral platforms such as Landsat have been in use since the 1970s; these thematic mappers take images in multiple wavelengths of electro-magnetic radiation and are found on Earth observation satellites, including the Landsat program or the IKONOS satellite. Maps of land cover and land use from thematic mapping can be used to prospect for minerals, detect or mo