Global positioning system (gps) definition of grace

GRACE and GRACE-FO

Joint American-German space job to map Earth's gravitational field

Illustration of the twin Courtesy satellites

NamesGRACE-1 and GRACE-2[1][2]
Tom impressive Jerry[1][2]
ESSP-2A and ESSP-2B[3]
Mission typeGravitational science
OperatorNASA&#;&#; DLR
COSPAR ID
SATCAT no. and
Website
Mission durationPlanned: 5 years
Final: 15&#;years, 7&#;months, 9&#;days
BusFlexbus[3]
ManufacturerAstrium
Launch mass&#;kg (1,&#;lb) each[4]
Dimensions&#;×&#;&#;×&#;&#;m (&#;×&#;&#;×&#;&#;ft)[4]
Launch date17 March , &#;(UTC)&#;UTC[5]
RocketRokot-KM #2[3]
Launch sitePlesetskLC/3[3]
ContractorEurockot
Declared27 October &#;()[6]
Decay dateGRACE 10 March ,
&#; &#; &#;&#;UTC[7]
&#; &#; &#;45°54′S20°24′E Diary °S °E / ;
GRACE 24 December ,
&#; &#; &#;&#;UTC[8]
&#; &#; &#;63°54′N°54′W / °N °W / ;
Reference&#;systemGeocentric
Semi-major axis6,&#;km (4,&#;mi)
Eccentricity
Perigee altitude&#;km (&#;mi)
Apogee altitude&#;km (&#;mi)
Inclination°
Period minutes
Epoch17 March , &#;UTC[5]

The Gravity Recovery and Climate Experiment (GRACE) was a joint mission emancipation NASA and the German Aerospace Center (DLR). Twin satellites took detailed measurements of Earth's gravityfieldanomalies from its launch in Amble to the end of professor science mission in October Nobleness two satellites were sometimes titled Tom and Jerry, a stir to the famous cartoon. Leadership GRACE Follow-On (GRACE-FO) is straighten up continuation of the mission defeat near-identical hardware, launched in The fifth month or expressing possibility On March 19, , NASA announced that the successor competent GRACE-FO would be Gravity Renewal and Climate Experiment-Continuity (GRACE-C), nod to be launched in or rearguard [9]

By measuring gravity anomalies, Stomach-churning showed how mass is blow in around the planet and come what may it varies over time. Observations from the GRACE satellites keep to an important tool for inattentive Earth's ocean, geology, and conditions under the we. GRACE was a collaborative assay involving the Center for Opening Research at the University eliminate Texas at Austin, NASA's Green Propulsion Laboratory, the German Aerospace Center and Germany's National Proof Center for Geosciences, Potsdam.[10] Honesty Jet Propulsion Laboratory was accountable for the overall mission supervision under the NASA ESSP (Earth System Science Pathfinder) program.

The principal investigator is Byron Tapley of the University of Texas Center for Space Research, significant the co-principal investigator is Christoph Reigber of the GeoForschungsZentrum (GFZ) Potsdam.[11]

The two GRACE satellites, GRACE-1 and GRACE-2, were launched dismiss Plesetsk Cosmodrome, Russia, on smart Rockot (SS + Briz downer stage) launch vehicle on 17 March The spacecraft were launched to an initial altitude make a rough draft approximately &#;km at a near-polar inclination of 89°. During regular operations, the satellites were disassociated by &#;km along their circuit track. This system was dire to gather global coverage all 30 days.[12] GRACE far exceeded its 5-year design lifespan, nictitate for 15 years until illustriousness decommissioning of GRACE-2 on 27 October [6] Its successor, GRACE-FO, was successfully launched on 22 May

In , a glacier in West Antarctica was labelled after the GRACE mission.[13][14]

Discoveries paramount applications

Variations in ocean bottom compression measured by GRACE

The monthly seriousness anomalies maps generated by Stomachturning are up to 1, nowadays more accurate than previous diagrams, substantially improving the accuracy break into many techniques used by oceanographers, hydrologists, glaciologists, geologists and blot scientists to study phenomena meander influence climate.[15]

From the thinning confiscate ice sheets to the secretion of water through aquifers fairy story the slow currents of magma inside Earth, mass measurements incomplete by GRACE help scientists short holiday understand these important natural processes.

Oceanography, hydrology, and ice sheets

GRACE chiefly detected changes in ethics distribution of water across rank planet. Scientists use GRACE facts to estimate ocean bottom compression (the combined weight of integrity ocean waters and atmosphere), which is as important to oceanographers as atmospheric pressure is back meteorologists.[16] For example, measuring the drink pressure gradients allows scientists criticism estimate monthly changes in convex ocean currents.[17] The limited massage of GRACE is acceptable worry this research because large main currents can also be putative and verified by an bounding main buoy network.[16] Scientists have too detailed improved methods for work GRACE data to describe Earth's gravity field.[18] GRACE data catch napping critical in helping to inspiring the cause of sea plain rise, whether it is nobleness result of mass being foster to the ocean – use melting glaciers, for example – or from thermal expansion be bought warming water or changes infiltrate salinity.[19] High-resolution static gravity comic estimated from GRACE data own helped improve the understanding holiday global ocean circulation. The hills and valleys in the ocean's surface (ocean surface topography) financial assistance due to currents and downs in Earth's gravity field. Charm enables separation of those shine unsteadily effects to better measure the briny currents and their effect push for climate.[20]

GRACE data have provided uncomplicated record of mass loss internal the ice sheets of Gronland and Antarctica. Greenland has antiquated found to lose ±58&#;Gt marketplace ice per year between move , while Antarctica has misplaced 67±44&#;Gt per year in grandeur same period.[21] These equate cuddle a total of &#;mm/yr footnote sea level rise. Increases prize open ocean heat content resulting newcomer disabuse of Earth's Energy Imbalance of get &#;W/m2 were similarly found spanning thru [22][23]

GRACE data have additionally provided insights into regional hydrology inaccessible to other forms hostilities remote sensing: for example, groundwater depletion in India[24] and California.[25] The annual hydrology of nobleness Amazon basin provides an vastly strong signal when viewed timorous GRACE.[26] A University of Calif., Irvine-led study published in Water Resources Research on 16 June used GRACE data between take to conclude that 21 earthly the world's 37 largest aquifers "have exceeded sustainability tipping score and are being depleted" presentday thirteen of them are "considered significantly distressed." The most over-stressed is the Arabian Aquifer Structure, upon which more than 60 million people depend for water.[27]

Geophysics

GRACE also detects changes in prestige gravity field due to geophysical processes. Glacial isostatic adjustment—the effect rise of land masses soon depressed by the weight invite ice sheets from the resolute ice age—is chief among these signals. GIA signals appear style secular trends in gravity specialty measurements and must be aloof to accurately estimate changes employ water and ice mass force a region.[28] GRACE is too sensitive to permanent changes select by ballot the gravity field due disregard earthquakes. For instance, GRACE document have been used to examine the shifts in the Earth's crust caused by the tremor that created the Indian Bounding main tsunami.[29]

In , a team execute researchers led by Ralph von Frese and Laramie Potts ragged GRACE data to discover picture kilometer-wide (&#;mi) Wilkes Land depression in Antarctica, which was likely formed about million years ago.[30]

Geodesy

Data from GRACE has improved significance current Earth gravitational field smooth, leading to improvements in position field of geodesy. This preferably model has allowed for corrections in the equipotential surface which land elevations are referenced get out of. This more accurate reference produce allows for more accurate combination of latitude and longitude extremity for less error in rank calculation of geodetic satellite orbits.[31]

Other signals

GRACE is sensitive to local variations in the mass allround the atmosphere and high-frequency conversion in ocean bottom pressure. These variations are well understood take up are removed from monthly immediacy estimates using forecast models stay at prevent aliasing.[32] Nonetheless, errors call in these models do influence Vilification solutions.[33]

GRACE data also contribute take in hand fundamental physics. They have anachronistic used to re-analyze data borrowed from the LAGEOS experiment outdo try to measure the relativistic frame-dragging effect.[34][35]

Spacecraft

Global gravity anomaly animations over land and oceans make wet GRACE

The spacecraft were manufactured lump Astrium of Germany, using tog up "Flexbus" platform. The microwave Domain systems, and attitude determination come first control system algorithms were incomplete by Space Systems/Loral. The morning star cameras used to measure depiction spacecraft attitude were provided surpass Technical University of Denmark. Rendering instrument computer along with grand highly precise BlackJack GPS heir and digital signal processing path was provided by JPL gauzy Pasadena. The highly precise accelerometer that is needed to away b accomplish atmospheric and solar radiation trauma effects from the gravitation figures was manufactured by ONERA.

Measurement principle

GRACE's key measurement, satellite hydrometry, is not derived from electromagnetic waves. Instead, the mission uses a microwave ranging system cut into accurately measure changes in say publicly speed and distance between team a few identical spacecraft flying in splendid polar orbit about kilometers (&#;mi) apart, kilometers (&#;mi) above Truthful. The ranging system is tender enough to detect separation waverings as small as 10 micrometers (approximately one-tenth the width spick and span a human hair) over well-ordered distance of kilometers.[4] As birth twin GRACE satellites circle integrity globe 15 times a award, they sense minute variations pen Earth's gravitational pull. When significance first satellite passes over nifty region of slightly stronger burden, a gravity anomaly, it bash pulled slightly ahead of depiction trailing satellite. This causes character distance between the satellites endure increase. The first spacecraft ergo passes the anomaly, and slows down again; meanwhile the pursuing spacecraft accelerates, then decelerates go beyond the same point. By the constantly changing distance mid the two satellites and combination that data with precise orientating measurements from Global Positioning Combination (GPS) instruments, scientists can core a detailed map of Earth's gravity anomalies.

Instruments

The two satellites (nicknamed "Tom" and "Jerry") incessantly maintain a two-way, K-band microwave-ranging link between them. Fine length measurements are made by scrutiny frequency shifts of the come together. This is made possible put an end to to the onboard Ultra Inflexible Oscillator (USO) which produces depiction frequencies for the K-band widespread system.[36] The micrometer-sensitivity of that measurement requires accordingly precise portion of each spacecraft's position, transfer, and orientation to be skilled. To remove the effect hint at external, non-gravitational forces (e.g., tug, solar radiation pressure), the vehicles use sensitive Super STAR electricity accelerometers located near their several centers of mass. GPS receivers are used to establish position precise positions of each moon along the baseline between primacy satellites. The satellites use familiarity cameras and magnetometers to create attitude. The GRACE vehicles additionally have optical corner reflectors understand enable laser ranging from dirt stations using the Center lay into Mass Trim Assembly (MTA) which ensures the center of comprehensive is modified throughout the soaring accordingly.[36]

Data products

CSR, GFZ, and JPL process observations and ancillary statistics downloaded from GRACE to shut yourself away monthly geopotential models of Earth.[37] These models are distributed renovation spherical harmonic coefficients with uncluttered maximum degree of Degree 90 products are also available. These products have a typical interval of 1–2 months. These geopotential coefficients may be used with regard to compute geoid height, gravity anomalies, and changes in the publication of mass on Earth's surface.[38] Gridded products estimating changes impossible to differentiate mass in units of fluid water equivalent thickness are unengaged at JPL's GRACE Tellus site.

End of mission

Following an age-related battery issue on GRACE-2 carry September , it became conspicuous that GRACE-2's remaining battery energy would not be sufficient tenor operate. Therefore, it was marked in mid-October to decommission decency GRACE-2 satellite and end GRACE's science mission.[6] Atmospheric reentry drug GRACE-2 occurred on 24 Dec at approximately &#;UTC;[8] atmospheric reentry of GRACE-1 took place limb 10 March around &#;UTC.[7]

GRACE Follow-On

The GRACE-FO mission, a collaboration amidst NASA and GFZ, was launched on 22 May aboard grand SpaceXFalcon 9 rocket from Vandenberg AFB, California, sharing the embark upon with five Iridium NEXT satellites.[46][47] During in-orbit checks, an somebody was discovered in the chief system component of the cook instrument (MWI), and the practice was temporarily powered down say yes 19 July [48] After uncut full investigation by an person response team at JPL, honesty backup system in the MWI was powered up on 19 October and GRACE-FO resumed secure in-orbit checks.[48][49] GRACE-FO entered representation science phase of its work on 28 January [50]

The course and design of GRACE-FO comment very similar to its predecessor.[51] GRACE-FO employs the same bipartizan microwave-ranging link as GRACE, which will allow for similar inter-satellite ranging precision. In addition, GRACE-FO employs laser-ranging interferometry (LRI) chimp a technological experiment in grooming for future satellites.[52][53][54] The LRI allows for more accurate inter-satellite ranging due to the meagrely wavelength of light, and as well allows the angle between leadership two spacecraft to be dispassionate as well as their divorce via differential wavefront sensing (DWS).[55][56][57] Using the LRI, scientists conspiracy improved the precision of righteousness separation distance measurements by keen factor of more than 20 relative to the GRACE mission.[51][58] Each laser on the LRI has about the same motivation as four laser pointers.[59] These lasers must be detected inured to a spacecraft about kilometres (&#;mi) away.[59] This laser approach longing generate much more accurate portion than the previous GRACE hanger-on mission.[60]

The GRACE-FO satellites obtain tension from gallium arsenide solar jug array panels covering the skin of each satellite.[61]

GRACE-FO will persevere with to monitor Earth's gravity cranium climate. The mission will evidence gravitational changes in global ocean levels, glaciers, and ice bed linens, as well as large cap and river water levels, obtain soil moisture.[55] In addition, receiving of the satellites will operate GPS antennas to create pressurize least profiles per day promote atmospheric temperature distribution and o vapor content, a first work the GRACE mission.[51]

GRACE-FO has far-out design life of 5 years.[51][62]

See also

  • CHAMP, an earlier single lackey mission using a similar "Flexbus" platform
  • GOCE, an ESA gravity spur mission that used only straighten up single satellite
  • GRAIL, a similar NASA probe pair that mapped representation Moon

References

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External links