Editing GRACE and GRACE-FO (section)

== Discoveries and applications ==
{{multiple image |align=left |direction=vertical
 |image1=Gravity anomalies on Earth.jpg |caption1=[[Gravity anomaly]] map from GRACE
 |image2=GRACE ocean bottom pressure.jpg |caption2=Variations in ocean bottom pressure measured by GRACE
}}

The monthly gravity anomalies maps generated by GRACE are up to 1,000 times more accurate than previous maps, substantially improving the accuracy of many techniques used by [[oceanography|oceanographer]]s, [[hydrology|hydrologists]], [[glaciology|glaciologists]], geologists and other scientists to study phenomena that influence climate.<ref>{{cite web |url=https://www.jpl.nasa.gov/news/new-gravity-mission-on-track-to-map-earths-shifty-mass |title=New Gravity Mission on Track to Map Earth's Shifty Mass |publisher=NASA/JPL|access-date=March 1, 2023}}</ref>

From the thinning of [[ice sheet]]s to the flow of water through [[aquifer]]s and the slow currents of [[magma]] inside Earth, mass measurements provided by GRACE help scientists better understand these important natural processes.

=== Oceanography, hydrology, and ice sheets ===
GRACE chiefly detected changes in the distribution of water across the planet. Scientists use GRACE data to estimate ocean bottom pressure (the combined weight of the ocean waters and atmosphere), which is as important to oceanographers as [[atmospheric pressure]] is to meteorologists.<ref name="nasa20151101">{{cite web |url=https://grace.jpl.nasa.gov/news/77/nasa-finds-new-way-to-track-ocean-currents-from-space/ |title=NASA Finds New Way to Track Ocean Currents from Space |publisher=NASA/Jet Propulsion Laboratory |first=Carol |last=Rasmussen |date=1 November 2015 |access-date=14 March 2018}}</ref> For example, measuring ocean pressure gradients allows scientists to estimate monthly changes in deep ocean currents.<ref>{{cite web |url=https://www.nasa.gov/audience/foreducators/k-4/features/F_Measuring_Gravity_With_Grace.html |title=Measuring Gravity With GRACE |publisher=NASA |first=Dan |last=Stillman |date=16 April 2007 |access-date=14 March 2018}}</ref> The limited resolution of GRACE is acceptable in this research because large ocean currents can also be estimated and verified by an ocean buoy network.<ref name="nasa20151101" /> Scientists have also detailed improved methods for using GRACE data to describe Earth's gravity field.<ref>{{cite journal |title=Improved methods for observing Earth's time variable mass distribution with GRACE using spherical cap mascons |journal=Journal of Geophysical Research: Solid Earth |first1=Michael M. |last1=Watkins |first2=David N. |last2=Weise |first3=Dah-Ning |last3=Yuan |first4=Carmen |last4=Boening |first5=Felix W. |last5=Landerer |display-authors=1 |volume=120 |issue=4 |pages=2648–2671 |date=April 2015 |doi=10.1002/2014JB011547 |bibcode=2015JGRB..120.2648W|doi-access=free }}</ref> GRACE data are critical in helping to determine the cause of [[sea level rise]], whether it is the result of mass being added to the ocean – from melting [[glacier]]s, for example – or from [[thermal expansion]] of warming water or changes in [[salinity]].<ref>{{cite web |url=http://www.jpl.nasa.gov/news/news.php?feature=1112 |title=NASA Missions Help Dissect Sea Level Rise |publisher=NASA/Jet Propulsion Laboratory |first=Rosemary |last=Sullivant |date=14 June 2006 |access-date=14 March 2018}}</ref>  High-resolution static gravity fields estimated from GRACE data have helped improve the understanding of global [[ocean current|ocean circulation]]. The hills and valleys in the ocean's surface ([[ocean surface topography]]) are due to currents and variations in Earth's gravity field. GRACE enables separation of those two effects to better measure ocean currents and their effect on climate.<ref name="oceanography">{{cite web |url=https://climate.nasa.gov/news/152/gravity-data-sheds-new-light-on-ocean-climate/ |title=Gravity data sheds new light on ocean, climate |publisher=NASA |first=Rosemary |last=Sullivant |date=26 August 2009 |access-date=14 March 2018}}</ref>

GRACE data have provided a record of mass loss within the [[ice sheet]]s of Greenland and Antarctica.  Greenland has been found to lose {{val|280|58|ul=Gt}} of ice per year between 2003 and 2013, while Antarctica has lost {{val|67|44|ul=Gt}} per year in the same period.<ref name="Velicogna et al. (2014)">{{cite journal |last1=Velicogna |first1=Isabella |author-link=Isabella Velicogna|last2=Sutterly |first2=T.C. |last3=van den Broeke |first3=M.R. |title=Regional acceleration in ice mass loss from Greenland and Antarctica using GRACE time-variable gravity data |journal=J. Geophys. Res. Space Phys. |date=2014 |issue=119 |pages=8130–8137 |doi=10.1002/2014GL061052 |bibcode=2014GeoRL..41.8130V |volume=41 |hdl=1874/308354 |s2cid=53062626 |hdl-access=free}}</ref> These equate to a total of 0.9&nbsp;mm/yr of sea level rise.  Increases in [[ocean heat content]] resulting from [[Earth's Energy Imbalance]] of about 0.8&nbsp;W/m<sup>2</sup> were similarly found spanning 2002 thru 2019.<ref>{{cite journal |last1=Marti |first1=Florence |last2=Blazquez |first2=Alejandro |last3=Meyssignac |first3=Benoit |last4=Ablain |first4=Michaël |last5=Barnoud |first5=Anne |last6=Fraudeau |first6=Robin |last7=Jugier |first7=Rémi |last8=Chenal |first8=Jonathan |last9=Larnicol |first9=Gilles |last10=Pfeffer |first10=Julia |last11=Restano |first11=Marco |last12=Benveniste |first12=Jérôme |display-authors=5 |title=Monitoring the ocean heat content change and the Earth energy imbalance from space altimetry and space gravimetry |journal=Earth System Science Data |year=2021 |doi=10.5194/essd-2021-220 |doi-access=free}}</ref><ref>{{cite journal |last1=Hakuba |first1=M.Z. |last2=Frederikse |first2=T. |last3=Landerer |first3=F.W. |title=Earth's Energy Imbalance From the Ocean Perspective (2005–2019) |journal=Geophysical Research Letters |volume=48 |issue=16 |date=28 August 2021 |doi=10.1029/2021GL093624 |doi-access=free|bibcode=2021GeoRL..4893624H }}</ref>  

GRACE data have also provided insights into regional hydrology inaccessible to other forms of remote sensing: for example, [[overdrafting|groundwater depletion]] in India<ref>{{cite journal |last1=Tiwari |first1=V.M. |last2=Wahr |first2=J. |author-link2=John M. Wahr |last3=Swenson |first3=S. |title=Dwindling groundwater resources in northern India, from satellite gravity observations |journal=Geophysical Research Letters |date=2009 |volume=36 |issue=18 |at=L18401 |doi=10.1029/2009GL039401 |bibcode=2009GeoRL..3618401T|doi-access= }}</ref> and California.<ref name="Famiglietti et al. (2011)">{{cite journal |last1=Famiglietti |first1=J |title=Satellites measure recent rates of groundwater depletion in California's Central Valley |journal=Geophys. Res. Lett. |date=2011 |volume=38 |issue=3 |at=L03403 |doi=10.1029/2010GL046442 |bibcode=2011GeoRL..38.3403F |url=https://escholarship.org/content/qt8g651992/qt8g651992.pdf?t=n0u8a0|doi-access=free }}</ref>  The annual hydrology of the [[Amazon basin]] provides an especially strong signal when viewed by GRACE.<ref name="Tapley et al. (2004)">{{cite journal |last1=Tapley |first1=Byron D. |last2=Bettadpur |first2=Srinivas |last3=Ries |first3=John C. |last4=Thompson |first4=Paul F. |last5=Watkins |first5=Michael M. |title=GRACE Measurements of Mass Variability in the Earth System |journal=Science |date=2004 |volume=305 |issue=5683 |pages=503–505 |doi=10.1126/science.1099192 |bibcode=2004Sci...305..503T |pmid=15273390 |s2cid=7357519 |url=https://authors.library.caltech.edu/52043/7/Tapley.SOM.pdf}}</ref>  A [[University of California, Irvine]]-led study published in ''[[Water Resources Research]]'' on 16 June 2015 used GRACE data between 2003 and 2013 to conclude that 21 of the world's 37 largest aquifers "have exceeded sustainability tipping points and are being depleted" and thirteen of them are "considered significantly distressed." The most over-stressed is the [[Arabian Aquifer System]], upon which more than 60 million people depend for water.<ref name="NASA_GRACE">{{cite web |url=http://www.jpl.nasa.gov/news/news.php?feature=4626 |title=Study: Third of Big Groundwater Basins in Distress |publisher=NASA |date=16 June 2015 |access-date=26 June 2015}}</ref>

=== Geophysics ===
[[File:15 Years of Freshwater Trends Seen by GRACE.webm|thumb|left|GRACE uses precise measurements of the motions of two spacecraft in Earth's orbit to track the movement of water through the oceans, land, and atmosphere.]]
[[File:Greenland+Antarctica Mass Loss.png|thumb|Change in mass of the Greenland and Antarctic ice sheets as measured by GRACE]]
GRACE also detects changes in the gravity field due to geophysical processes. [[Glacial isostatic adjustment]]—the slow rise of land masses once depressed by the weight of ice sheets from the last ice age—is chief among these signals.  GIA signals appear as secular trends in gravity field measurements and must be removed to accurately estimate changes in water and ice mass in a region.<ref>{{cite journal |last1=Tregoning |last2=Ramillien |last3=McQueen |last4=Zwartz |s2cid=15724840 |title=Glacial isostatic adjustment and nonstationary signals observed by GRACE |journal=J. Geophys. Res. |date=2009 |volume=114 |issue=B6 |pages=B06406 |doi=10.1029/2008JB006161 |bibcode=2009JGRB..114.6406T|doi-access=free }}</ref>  GRACE is also sensitive to permanent changes in the gravity field due to earthquakes.  For instance, GRACE data have been used to analyze the shifts in the Earth's crust caused by the earthquake that created the 2004 Indian Ocean tsunami.<ref>{{cite news |url=https://www.nytimes.com/2006/08/08/science/08find.html |title=Before the '04 Tsunami, an Earthquake So Violent It Even Shook Gravity |work=The New York Times |first=Kenneth |last=Chang |date=8 August 2006 |access-date=4 May 2010}}</ref>

In 2006, a team of researchers led by Ralph von Frese and Laramie Potts used GRACE data to discover the {{convert|480|km|mi|sp=us|adj=mid|-wide}} [[Wilkes Land crater]] in [[Antarctica]], which was probably formed about 250 million years ago.<ref>{{cite web |url=http://researchnews.osu.edu/archive/erthboom.htm |title=Big Bang in Antarctica—Killer Crater Found Under Ice |publisher=Ohio State University |url-status=dead |archive-url=https://web.archive.org/web/20160306140004/http://researchnews.osu.edu/archive/erthboom.htm |archive-date=6 March 2016}}</ref>

{{clear|left}}
=== Geodesy ===
Data from GRACE has improved the current [[Earth Gravitational Model|Earth gravitational field model]], leading to improvements in the field of [[geodesy]]. This improved model has allowed for corrections in the equipotential surface which land elevations are referenced from. This more accurate reference surface allows for more accurate coordinates of latitude and longitude and for less error in the calculation of geodetic satellite orbits.<ref>{{Cite web |url=http://www2.csr.utexas.edu/grace/gravity/geodesy.html |title=GRACE – Gravity Recovery and Climate Experiment |publisher=University of Texas Center for Space Research |access-date=21 March 2018}}</ref>

=== Other signals ===
GRACE is sensitive to regional variations in the mass of the atmosphere and high-frequency variation in ocean bottom pressure.  These variations are well understood and are removed from monthly gravity estimates using [[numerical weather prediction|forecast models]] to prevent [[aliasing]].<ref>{{cite web |title=GRACE AOD1B |url=http://www.gfz-potsdam.de/en/aod1b/ |website=gfz-potsdam.de |publisher=[[GFZ German Research Centre for Geosciences]] |access-date=11 June 2015}}</ref>  Nonetheless, errors in these models do influence GRACE solutions.<ref>{{cite book |last1=Ge |first1=Shengjie |title=GPS radio occultation and the role of atmospheric pressure on spaceborne gravity estimation over Antarctica |date=2006 |publisher=Ohio State University |url=https://etd.ohiolink.edu/ap/10?0::NO:10:P10_ACCESSION_NUM:osu1149070384 |access-date=11 June 2015 |archive-date=13 June 2015 |archive-url=https://web.archive.org/web/20150613134056/https://etd.ohiolink.edu/ap/10?0::NO:10:P10_ACCESSION_NUM:osu1149070384 |url-status=dead }}</ref>

GRACE data also contribute to fundamental physics. They have been used to re-analyze data obtained from the [[LAGEOS]] experiment to try to measure the relativistic [[frame-dragging]] effect.<ref>{{cite journal |last1=Ciufolini |first1=I. |last2=Pavlis |first2=E.C. |year=2004 |title=A confirmation of the general relativistic prediction of the Lense–Thirring effect |url=http://www.dm.unipi.it/cluster-pages/tommei/mc/Lensenature03007.pdf |journal=Nature |volume=431 |issue=7011 |pages=958–960 |doi=10.1038/nature03007 |pmid=15496915 |bibcode=2004Natur.431..958C |s2cid=4423434 |url-status=dead |archive-url=https://web.archive.org/web/20150613230457/http://www.dm.unipi.it/cluster-pages/tommei/mc/Lensenature03007.pdf |archive-date=13 June 2015}}</ref><ref>{{cite journal |last1=Ciufolini |first1=I. |last2=Pavlis |first2=E.C. |last3=Peron |first3=R. |year=2006 |title=Determination of frame-dragging using Earth gravity models from CHAMP and GRACE |journal=New Astron |volume=11 |issue=8 |pages=527–550 |doi=10.1016/j.newast.2006.02.001 |bibcode=2006NewA...11..527C}}</ref>