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68-474: Jason-1 was a satellite altimeter oceanography mission. It sought to monitor global ocean circulation , study the ties between the ocean and the atmosphere , improve global climate forecasts and predictions, and monitor events such as El Niño and ocean eddies . Jason-1 was launched in 2001 and it was followed by OSTM/Jason-2 in 2008, and Jason-3 in 2016 – the Jason satellite series . Jason-1

136-465: A few meters. The most prominent system, GPS , consists of a constellation of 31 satellites (as of December 2013) in high, 12-hour circular orbits, distributed in six planes with 55° inclinations . The principle of location is based on trilateration . Each satellite transmits a precise ephemeris with information on its own position and a message containing the exact time of transmission. The receiver compares this time of transmission with its own clock at

204-428: A key figure of merit of the solar panels is the specific power (watts generated divided by solar array mass), which indicates on a relative basis how much power one array will generate for a given launch mass relative to another. Another key metric is stowed packing efficiency (deployed watts produced divided by stowed volume), which indicates how easily the array will fit into a launch vehicle. Yet another key metric

272-625: A number of variations which may be used for specific purposes such as gravity field investigations and orbit improvement. These examples present a few of the possibilities for the application of satellite-to-satellite tracking. Satellite-to-satellite tracking data was first collected and analyzed in a high-low configuration between ATS-6 and GEOS-3 . The data was studied to evaluate its potential for both orbit and gravitational model refinement.       Example: GRACE       Examples: CHAMP , GOCE [REDACTED] This article incorporates text from this source, which

340-589: A point is a tensor , since it is the derivative of each component of the gravity vector taken in each sensitive axis. Thus, the value of any component of the gravity vector can be known all along the path of the vehicle if gravity gradiometers are included in the system and their outputs are integrated by the system computer. An accurate gravity model will be computed in real-time and a continuous map of normal gravity, elevation, and anomalous gravity will be available.       Example: GOCE This technique uses satellites to track other satellites. There are

408-508: A position-tracking antenna were built in France. The radiometer, Global Positioning System receiver and laser retroreflector array were built in the United States. TOPEX/Poseidon and Jason-1 have led to major advances in the science of physical oceanography and in climate studies. Their 15-year data record of ocean surface topography has provided the first opportunity to observe and understand

476-481: A quasi-steady, large-scale pattern of global ocean circulation by proving that the ocean is changing rapidly on all scales, from huge features such as El Niño and La Niña, which can cover the entire equatorial Pacific, to tiny eddies swirling off the large Gulf Stream in the Atlantic. Measurements by Jason-1 indicate that mean sea level has been rising at an average rate of 2.28 mm (0.09 inch) per year since 2001. This

544-445: A satellite, or flashing light on the satellite, against a background of stars. The stars, whose positions were accurately determined, provided a framework on the photographic plate or film for a determination of precise directions from camera station to satellite. Geodetic positioning work with cameras was usually performed with one camera observing simultaneously with one or more other cameras. Camera systems are weather dependent and that

612-448: A small toy Ferris wheel and a solar powered radio transmitter. They were initially about 6% efficient, but improvements began to raise this number almost immediately. Bell had been interested in the idea as a system to provide power at remote telephone repeater stations, but the cost of the devices was far too high to be practical in this role. Aside from small experimental kits and uses, the cells remained largely unused. This changed with

680-415: A wide variety of uses from basic scientific research on climate to ship routing. Applications include: Satellite altimeter The main goals of satellite geodesy are: Satellite geodetic data and methods can be applied to diverse fields such as navigation , hydrography , oceanography and geophysics . Satellite geodesy relies heavily on orbital mechanics . Satellite geodesy began shortly after

748-529: Is Earth's primary storehouse of solar energy. Jason-1's measurements of sea surface height reveal where this heat is stored, how it moves around Earth by ocean currents, and how these processes affect weather and climate. Jason-1 was launched on 7 December 2001 from Vandenberg Air Force Base , in California , aboard a Delta II Launch vehicle . During the first months Jason-1 shared an almost identical orbit to TOPEX/Poseidon, which allowed for cross calibration. At

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816-718: Is a radar technique used in geodesy and remote sensing . This geodetic method uses two or more synthetic aperture radar (SAR) images to generate maps of surface deformation or digital elevation , using differences in the phase of the waves returning to the satellite. The technique can potentially measure centimetre-scale changes in deformation over timespans of days to years. It has applications for geophysical monitoring of natural hazards, for example earthquakes, volcanoes and landslides, and also in structural engineering, in particular monitoring of subsidence and structural stability.       Example: Seasat , TerraSAR-X A gravity gradiometer can independently determine

884-415: Is affected by natural climate variability, as well as by human activities. TOPEX/Poseidon and Jason-1 made clear the importance of planetary-scale waves, such as Rossby and Kelvin waves. No one had realized how widespread these waves are. Thousands of kilometers wide, these waves are driven by wind under the influence of Earth's rotation and are important mechanisms for transmitting climate signals across

952-499: Is also used for monitoring Earth's rotation , polar motion , and crustal dynamics. The presence of the GPS signal in space also makes it suitable for orbit determination and satellite-to-satellite tracking.       Examples: GPS , GLONASS , Galileo Doppler positioning involves recording the Doppler shift of a radio signal of stable frequency emitted from a satellite as

1020-486: Is cost (dollars per watt). To increase the specific power, typical solar panels on spacecraft use close-packed solar cell rectangles that cover nearly 100% of the Sun-visible area of the solar panels, rather than the solar wafer circles which, even though close-packed, cover about 90% of the Sun-visible area of typical solar panels on Earth. However, some solar panels on spacecraft have solar cells that cover only 30% of

1088-483: Is in the public domain : Defense Mapping Agency (1983). Geodesy for the Layman (PDF) (Report). United States Air Force. Archived from the original (PDF) on 2017-05-13 . Retrieved 2021-02-19 . Solar panels on spacecraft Spacecraft operating in the inner Solar System usually rely on the use of power electronics -managed photovoltaic solar panels to derive electricity from sunlight . Outside

1156-494: Is one major reason why they fell out of use by the 1980s.       Examples: PAGEOS , Project Echo , ANNA 1B In satellite laser ranging (SLR) a global network of observation stations measure the round trip time of flight of ultrashort pulses of light to satellites equipped with retroreflectors . This provides instantaneous range measurements of millimeter level precision which can be accumulated to provide accurate orbit parameters, gravity field parameters (from

1224-608: Is somewhat less than the rate measured by the earlier TOPEX/Poseidon mission, but over four times the rate measured by the later Envisat mission. Mean sea level measurements from Jason-1 are continuously graphed at the Centre National d'Études Spatiales web site, on the Aviso page . A composite sea level graph, using data from several satellites, is also available on that site . The data record from these altimetry missions has given scientists important insights into how global sea level

1292-484: Is the first mission to Jupiter (arrived at Jupiter on July 4, 2016) to use solar panels instead of the traditional RTGs that are used by previous outer Solar System missions, making it the furthest spacecraft to use solar panels to date. It has 50 square metres (540 sq ft) of panels. The InSight lander , Ingenuity helicopter , Tianwen-1 orbiter , and Zhurong rover all currently operating on Mars also utilize solar panels. Another spacecraft of interest

1360-657: The Argonauts . [1] Archived 25 March 2016 at the Wayback Machine [2] [3] [REDACTED] This article incorporates text from this source, which is in the public domain . Jason-1 is the successor to the TOPEX/Poseidon mission, which measured ocean surface topography from 1992 through 2005. Like its predecessor, Jason-1 is a joint project between the NASA (United States) and CNES (France) space agencies. Jason-1's successor,

1428-486: The Earth's radiation belts (also called Van Allen belts), galactic cosmic rays (GCR), solar wind and solar flares . The Van Allen belts and the solar wind contain mostly protons and electrons, while GCR are in majority very high energy protons, alpha particles and heavier ions. Solar panels will experience efficiency degradation over time as a result of these types of radiation, but the degradation rate will depend strongly on

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1496-677: The Ocean Surface Topography Mission on the Jason-2 satellite, was launched in June 2008. These satellites provide a unique global view of the oceans that is impossible to acquire using traditional ship-based sampling. Jason-1 was built by Thales Alenia Space using a Proteus platform, under a contract from CNES , as well as the main Jason-1 instrument, the Poseidon-2 altimeter (successor to

1564-601: The geocentric position of an Earth satellite, allowing for the precise calibration of radar altimeters and separation of long-term instrumentation drift from secular changes in ocean surface topography . Satellite laser ranging contributes to the definition of the international terrestrial reference frames by providing the information about the scale and the origin of the reference frame, the so-called geocenter coordinates.       Example: LAGEOS Satellites such as Seasat (1978) and TOPEX/Poseidon (1992-2006) used advanced dual-band radar altimeters to measure

1632-416: The ionosphere . Spaceborne radar altimeters have proven to be superb tools for mapping ocean-surface topography , the hills and valleys of the sea surface. These instruments send a microwave pulse to the ocean's surface and record the time it takes to return. A microwave radiometer corrects any delay that may be caused by water vapor in the atmosphere . Other corrections are also required to account for

1700-556: The 20 MHz Mayak transmitter and Sergei Vernov's Scintillation counter , and these functioned for the entire lifetime of the satellite; until it reentered the Atmosphere nearly two years later. The success of the Vanguard system inspired Spectrolab , an optics company, to take up the development of solar cells specifically designed for space applications. They had their first major design win on Pioneer 1 in 1958, and would later be

1768-558: The Earth's gravity. In DORIS , the ground station emits the signal and the satellite receives.       Examples: Transit , DORIS , Argos In optical triangulation, the satellite can be used as a very high target for triangulation and can be used to ascertain the geometric relationship between multiple observing stations. Optical triangulation with the BC-4, PC-1000, MOTS, or Baker Nunn cameras consisted of photographic observations of

1836-589: The Earth-orbiting, Hubble Space Telescope . The Rosetta space probe , launched 2 March 2004, used its 64 square metres (690 sq ft) of solar panels as far as the orbit of Jupiter (5.25 AU ); previously the furthest use was the Stardust spacecraft at 2 AU. Solar power for propulsion was also used on the European lunar mission SMART-1 with a Hall effect thruster . The Juno mission, launched in 2011,

1904-517: The Poseidon altimeter on-board TOPEX/Poseidon). Jason-1 was designed to measure climate change through very precise millimeter-per-year measurements of global sea level changes . As did TOPEX/Poseidon, Jason-1 uses an altimeter to measure the hills and valleys of the ocean's surface. These measurements of sea surface topography allow scientists to calculate the speed and direction of ocean currents and monitor global ocean circulation. The global ocean

1972-609: The Sun-visible area. Solar panels need to have a lot of surface area that can be pointed towards the Sun as the spacecraft moves. More exposed surface area means more electricity can be converted from light energy from the Sun. Since spacecraft have to be small, this limits the amount of power that can be produced. All electrical circuits generate waste heat ; in addition, solar arrays act as optical and thermal as well as electrical collectors. Heat must be radiated from their surfaces. High-power spacecraft may have solar arrays that compete with

2040-418: The active payload itself for thermal dissipation. The innermost panel of arrays may be "blank" to reduce the overlap of views to space. Such spacecraft include the higher-power communications satellites (e.g., later-generation TDRS ) and Venus Express , not high-powered but closer to the Sun. Spacecraft are built so that the solar panels can be pivoted as the spacecraft moves. Thus, they can always stay in

2108-465: The components of the gravity vector on a real-time basis. A gravity gradient is simply the spatial derivative of the gravity vector. The gradient can be thought of as the rate of change of a component of the gravity vector as measured over a small distance. Hence, the gradient can be measured by determining the difference in gravity at two close but distinct points. This principle is embodied in several recent moving-base instruments. The gravity gradient at

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2176-403: The development of permanent geodetic networks and reference frames. Dedicated satellites were launched to measure Earth's gravity field in the 2000s, such as CHAMP , GRACE , and GOCE . Techniques of satellite geodesy may be classified by instrument platform: A satellite may Global navigation satellite systems are dedicated radio positioning services, which can locate a receiver to within

2244-518: The development of the first US spacecraft, the Vanguard 1 satellite in 1958. Calculations by Dr. Hans Ziegler demonstrated that a system using solar cells recharging a battery pack would provide the required power in a much lighter overall package than using just a battery. The satellite was powered by silicon solar cells with ≈10% conversion efficiency. A few weeks after the US launched Vanguard 1, Sputnik 3

2312-400: The direct path of the light rays no matter how the spacecraft is pointed. Spacecraft are usually designed with solar panels that can always be pointed at the Sun, even as the rest of the body of the spacecraft moves around, much as a tank turret can be aimed independently of where the tank is going. A tracking mechanism is often incorporated into the solar arrays to keep the array pointed towards

2380-422: The early 1990s, Gallium arsenide -based solar cells became favored over silicon because they have a higher efficiency and degrade more slowly than silicon in the space radiation environment. The most efficient solar cells currently in production are now multi-junction photovoltaic cells . These use a combination of several layers of indium gallium phosphide, gallium arsenide and germanium to harvest more energy from

2448-502: The end of this period, the older satellite was moved to a new orbit midway between each Jason ground track . Jason had a repeat cycle of 10 days. On 16 March 2002, Jason-1 experienced a sudden attitude upset, accompanied by temporary fluctuations in the onboard electrical systems. Soon after this incident, two new small pieces of space debris were observed in orbits slightly lower than Jason-1's, and spectroscopic analysis eventually proved them to have originated from Jason-1. In 2011, it

2516-656: The first cells to travel to the Moon, on the Apollo 11 mission's ALSEP package. As satellites grew in size and power, Spectrolab began looking for ways to introduce much more powerful cells. This led them to pioneer the development of multi-junction cells that increased efficiency from around 12% for their 1970s silicon cells to about 30% for their current gallium arsenide (GaAs) cells. These types of cells are now used almost universally on all solar-powered spacecraft. Solar panels on spacecraft supply power for two main uses: For both uses,

2584-525: The first of the US Army 's SECOR (Sequential Collation of Range) instruments. These missions led to the accurate determination of the leading spherical harmonic coefficients of the geopotential, the general shape of the geoid , and linked the world's geodetic datums. Soviet military satellites undertook geodesic missions to assist in ICBM targeting in the late 1960s and early 1970s. The Transit satellite system

2652-452: The global change of ocean circulation and sea level. The results have improved the understanding of the role of the ocean in climate change and improved weather and climate predictions. Data from these missions are used to improve ocean models, forecast hurricane intensity, and identify and track large ocean/atmosphere phenomena such as El Niño and La Niña . The data are also used every day in applications as diverse as routing ships, improving

2720-420: The globe to within 2.5 centimeters (1 inch). This new knowledge has revised notions about how tides dissipate. Instead of losing all their energy over shallow seas near the coasts, as previously believed, about one third of tidal energy is actually lost to the deep ocean. There, the energy is consumed by mixing water of different properties, a fundamental mechanism in the physics governing the general circulation of

2788-455: The height of the Earth's surface (sea, ice, and terrestrial surfaces) from a spacecraft . Jason-1 began in 2001, Jason-2 in 2008 and Jason-3 in January 2016. That measurement, coupled with orbital elements (possibly augmented by GPS), enables determination of the terrain . The two different wavelengths of radio waves used permit the altimeter to automatically correct for varying delays in

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2856-414: The influence of electrons in the ionosphere and the dry air mass of the atmosphere. Combining these data with the precise location of the spacecraft makes it possible to determine sea-surface height to within a few centimeters (about one inch). The strength and shape of the returning signal also provides information on wind speed and the height of ocean waves. These data are used in ocean models to calculate

2924-416: The large ocean basins. At high latitudes, they travel twice as fast as scientists believed previously, showing the ocean responds much more quickly to climate changes than was known before these missions. The precise measurements of TOPEX/Poseidon's and Jason-1 have brought knowledge of ocean tides to an unprecedented level. The change of water level due to tidal motion in the deep ocean is known everywhere on

2992-474: The launch of Sputnik in 1957. Observations of Explorer 1 and Sputnik 2 in 1958 allowed for an accurate determination of Earth's flattening . The 1960s saw the launch of the Doppler satellite Transit-1B and the balloon satellites Echo 1 , Echo 2, and PAGEOS . The first dedicated geodetic satellite was ANNA-1B , a collaborative effort between NASA , the DoD , and other civilian agencies. ANNA-1B carried

3060-497: The ocean that OSTM/Jason-2 flew over five days earlier. Its ground tracks fell midway between those of OSTM/Jason-2, which are about 315 km (196 mi) apart at the equator . This interleaved tandem mission provided twice the number of measurements of the ocean's surface, bringing smaller features such as ocean eddies into view. The tandem mission also helped pave the way for a future ocean altimeter mission that would collect much more detailed data with its single instrument than

3128-539: The ocean. TOPEX/Poseidon and Jason-1 observations provided the first global data for improving the performance of the numerical ocean models that are a key component of climate prediction models. TOPEX/Poseidon and Jason-1 data are available at the University of Colorado Center for Astrodynamics Research, NASA's Physical Oceanography Distributed Active Archive Center, and the French data archive center AVISO. Altimetry data have

3196-456: The operation of solar-powered spacecraft feasible at larger distances from the sun. Solar array mass could be reduced with thin-film photovoltaic cells, flexible blanket substrates, and composite support structures. Solar array efficiency could be improved by using new photovoltaic cell materials and solar concentrators that intensify the incident sunlight. Photovoltaic concentrator solar arrays for primary spacecraft power are devices which intensify

3264-543: The orbit of Jupiter , solar radiation is too weak to produce sufficient power within current solar technology and spacecraft mass limitations, so radioisotope thermoelectric generators (RTGs) are instead used as a power source. The first practical silicon-based solar cells were introduced by Russell Shoemaker Ohl, a researcher at Bell Labs in 1940. It was only 1% efficient. In April 25, 1954 in Murray Hill, New Jersey. They demonstrated their solar panel by using it to power

3332-465: The orbit perturbations), Earth rotation parameters, tidal Earth's deformations, coordinates and velocities of SLR stations, and other substantial geodetic data. Satellite laser ranging is a proven geodetic technique with significant potential for important contributions to scientific studies of the Earth/Atmosphere/Oceans system. It is the most accurate technique currently available to determine

3400-413: The round-trip flight-time of a microwave pulse between the satellite and the Earth's surface to determine the distance between the spacecraft and the surface. From this distance or height, the local surface effects such as tides, winds and currents are removed to obtain the satellite height above the geoid. With a precise ephemeris available for the satellite, the geocentric position and ellipsoidal height of

3468-399: The safety and efficiency of offshore industry operations, managing fisheries, and tracking marine mammals. TOPEX/Poseidon and Jason-1 have made major contributions to the understanding of: The missions revealed the surprising variability of the ocean, how much it changes from season to season, year to year, decade to decade and on even longer time scales. They ended the traditional notion of

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3536-671: The safety and efficiency of offshore industry operations, managing fisheries, and tracking marine mammals. Their 15-year data record of ocean surface topography has provided the first opportunity to observe and understand the global change of ocean circulation and sea level. The results have improved the understanding of the role of the ocean in climate change and improved weather and climate predictions. Data from these missions are used to improve ocean models, forecast hurricane intensity, and identify and track large ocean/atmosphere phenomena such as El Niño and La Niña. The data are also used every day in applications as diverse as routing ships, improving

3604-445: The satellite approaches and recedes from the observer. The observed frequency depends on the radial velocity of the satellite relative to the observer, which is constrained by orbital mechanics . If the observer knows the orbit of the satellite, then recording the Doppler profile determines the observer's position. Conversely, if the observer's position is precisely known, then the orbit of the satellite can be determined and used to study

3672-562: The satellite are available for any given observation time. It is then possible to compute the geoid height by subtracting the measured altitude from the ellipsoidal height. This allows direct measurement of the geoid, since the ocean surface closely follows the geoid. The difference between the ocean surface and the actual geoid gives ocean surface topography .       Examples: Seasat , Geosat , TOPEX/Poseidon , ERS-1 , ERS-2 , Jason-1 , Jason-2 , Envisat , SWOT (satellite) Interferometric synthetic aperture radar (InSAR)

3740-487: The solar cell technology and on the location of the spacecraft. With borosilicate glass panel coverings, this may be between 5-10% efficiency loss per year. Other glass coverings, such as fused silica and lead glasses, may reduce this efficiency loss to less than 1% per year. The degradation rate is a function of the differential flux spectrum and the total ionizing dose. Up until the early 1990s, solar arrays used in space primarily used crystalline silicon solar cells. Since

3808-483: The solar spectrum. Leading edge multi-junction cells are capable of exceeding 39.2% under non-concentrated AM1.5G illumination and 47.1% using concentrated AM1.5G illumination. To date, solar power, other than for propulsion, has been practical for spacecraft operating no farther from the Sun than the orbit of Jupiter . For example, Juno , Magellan , Mars Global Surveyor , and Mars Observer used solar power as does

3876-416: The speed and direction of ocean currents and the amount and location of heat stored in the ocean, which in turn reveals global climate variations . A laser altimeter uses the round-trip flight-time of a beam of light at optical or infrared wavelengths to determine the spacecraft's altitude or, conversely, the ground topography.       Examples: ICESat , MOLA . A radar altimeter uses

3944-455: The station and the fourth set of arrays were installed in March 2009. 240 kilowatts of electricity can be generated from these solar arrays. That comes to 120 kilowatts average system power, including 50% ISS time in Earth's shadow. For future missions, it is desirable to reduce solar array mass, and to increase the power generated per unit area. This will reduce overall spacecraft mass, and may make

4012-579: The sun. Sometimes, satellite operators purposefully orient the solar panels to "off point," or out of direct alignment from the Sun. This happens if the batteries are completely charged and the amount of electricity needed is lower than the amount of electricity made; off-pointing is also sometimes used on the International Space Station for orbital drag reduction . Space contains varying levels of great electromagnetic radiation as well as ionizing radiation . There are 4 sources of radiations:

4080-436: The sunlight on the photovoltaics. This design uses a flat lens, called a Fresnel lens , which takes a large area of sunlight and concentrates it onto a smaller spot, allowing a smaller area of solar cell to be used. Solar concentrators put one of these lenses over every solar cell. This focuses light from the large concentrator area down to the smaller cell area. This allows the quantity of expensive solar cells to be reduced by

4148-410: The time of reception and multiplies the difference by the speed of light to obtain a " pseudorange ." Four pseudoranges are needed to obtain the precise time and the receiver's position within a few meters. More sophisticated methods, such as real-time kinematic (RTK) can yield positions to within a few millimeters. In geodesy, GNSS is used as an economical tool for surveying and time transfer . It

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4216-470: The two Jason satellites now do together. In early 2012, having helped cross-calibrate the OSTM/Jason-2 replacement mission, Jason-1 was maneuvered into its graveyard orbit and all remaining fuel was vented. The mission was still able to return science data, measuring Earth's gravity field over the ocean. On 21 June 2013, contact with Jason-1 was lost; multiple attempts to re-establish communication failed. It

4284-405: Was Dawn which went into orbit around 4 Vesta in 2011. It used ion thrusters to get to Ceres . The potential for solar powered spacecraft beyond Jupiter has been studied. The International Space Station also uses solar arrays to power everything on the station. The 262,400 solar cells cover around 27,000 square feet (2,500 m ) of space. There are four sets of solar arrays that power

4352-502: Was determined that the last remaining transmitter on board the spacecraft had failed. Operators sent commands to the satellite to turn off remaining functioning components on 1 July 2013, rendering it decommissioned. It is estimated that the spacecraft will remain on orbit for at least 1,000 years. The program is named after the Greek mythological hero Jason . Jason-1 has five 5 instruments: The Jason-1 satellite, its altimeter instrument and

4420-470: Was determined that the pieces of debris had most likely been ejected from Jason-1 by an unidentified, small "high-speed particle" hitting one of the spacecraft's solar panels . Orbit maneuvers in 2009 put the Jason-1 satellite on the opposite side of Earth from the OSTM/Jason-2 satellite, which is operated by the United States and French weather agencies. At that time, Jason-1 flew over the same region of

4488-570: Was launched alongside the TIMED spacecraft. The lineage of the name begins with the JASO1 meeting (JASO=Journées Altimétriques Satellitaires pour l'Océanographie) in Toulouse , France to study the problems of assimilating altimeter data in models. Jason as an acronym also stands for "Joint Altimetry Satellite Oceanography Network". Additionally, it is used to reference the mythical quest for knowledge of Jason and

4556-472: Was launched by the Soviet space program outfitted with Silver zinc batteries with experimental silicon solar cells. The purpose of the batteries was both to power the transmitter and other equipment, but also to test the long term effects of radiation and micrometeorite damage on solar batteries. Some of the batteries were covered with protective glass while others were left exposed. The batteries were able to power

4624-618: Was used extensively for Doppler surveying, navigation, and positioning. Observations of satellites in the 1970s by worldwide triangulation networks allowed for the establishment of the World Geodetic System . The development of GPS by the United States in the 1980s allowed for precise navigation and positioning and soon became a standard tool in surveying. In the 1980s and 1990s satellite geodesy began to be used for monitoring of geodynamic phenomena, such as crustal motion , Earth rotation , and polar motion . The 1990s were focused on

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