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Literature review Evaluating information Staying current Citations and references Referencing software Understanding plagiarism Academic study and writing. Supports for About the Library. 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. GRACE data have also provided insights into regional hydrology inaccessible to other forms of remote sensing: for example, groundwater depletion in India [20] and California. A University of California, Irvine -led study published in Water Resources Research on 16 June used GRACE data between and 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.

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. For instance, GRACE data have been used to analyze the shifts in the Earth's crust caused by the earthquake that created the Indian Ocean tsunami.

Data from GRACE has improved the current 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.

GRACE is sensitive to regional variations in the mass of the atmosphere and high-frequency variation in ocean bottom pressure.

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These variations are well understood and are removed from monthly gravity estimates using forecast models to prevent aliasing. 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. The spacecraft were manufactured by Astrium of Germany , using its "Flexbus" platform.

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The star cameras used to measure the spacecraft attitude were provided by Technical University of Denmark. The highly precise accelerometer that is needed to separate atmospheric and solar radiation pressure effects from the gravitation data was manufactured by ONERA. The ranging system is sensitive enough to detect separation changes as small as 10 micrometers approximately one-tenth the width of a human hair over a distance of kilometers.

SNET mission: S-Band network of distributed nano satellites

When the first satellite passes over a region of slightly stronger gravity, a gravity anomaly , it is pulled slightly ahead of the trailing satellite. This causes the distance between the satellites to increase.

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The first spacecraft then passes the anomaly, and slows down again; meanwhile the following spacecraft accelerates, then decelerates over the same point. By measuring the constantly changing distance between the two satellites and combining that data with precise positioning measurements from Global Positioning System GPS instruments, scientists can construct a detailed map of Earth's gravity anomalies. The two satellites nicknamed "Tom" and "Jerry" constantly maintain a two-way, K-band microwave-ranging link between them. Fine distance measurements are made by comparing frequency shifts of the link.

To remove the effect of external, non-gravitational forces e. GPS receivers are used to establish the precise positions of each satellite along the baseline between the satellites. The satellites use star cameras and magnetometers to establish attitude. The GRACE vehicles also have optical corner reflectors to enable laser ranging from ground stations using the Center of Mass Trim Assembly MTA which ensures the center of mass is modified throughout the flight accordingly.

Degree 90 products are also available. These products have a typical latency of 1—2 months. These geopotential coefficients may be used to compute geoid height, gravity anomalies, and changes in the distribution of mass on Earth's surface.

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The mission will track gravitational changes in global sea levels, glaciers, and ice sheets, as well as large lake and river water levels, and soil moisture. From Wikipedia, the free encyclopedia. Play media. Spaceflight portal. 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 forecast models to prevent aliasing.

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. The spacecraft were manufactured by Astrium of Germany , using its "Flexbus" platform. The star cameras used to measure the spacecraft attitude were provided by Technical University of Denmark. The highly precise accelerometer that is needed to separate atmospheric and solar radiation pressure effects from the gravitation data was manufactured by ONERA.

The ranging system is sensitive enough to detect separation changes as small as 10 micrometers approximately one-tenth the width of a human hair over a distance of kilometers. When the first satellite passes over a region of slightly stronger gravity, a gravity anomaly , it is pulled slightly ahead of the trailing satellite. This causes the distance between the satellites to increase.

The first spacecraft then passes the anomaly, and slows down again; meanwhile the following spacecraft accelerates, then decelerates over the same point. By measuring the constantly changing distance between the two satellites and combining that data with precise positioning measurements from Global Positioning System GPS instruments, scientists can construct a detailed map of Earth's gravity anomalies.

The two satellites nicknamed "Tom" and "Jerry" constantly maintain a two-way, K-band microwave-ranging link between them. Fine distance measurements are made by comparing frequency shifts of the link. To remove the effect of external, non-gravitational forces e. GPS receivers are used to establish the precise positions of each satellite along the baseline between the satellites. The satellites use star cameras and magnetometers to establish attitude. The GRACE vehicles also have optical corner reflectors to enable laser ranging from ground stations using the Center of Mass Trim Assembly MTA which ensures the center of mass is modified throughout the flight accordingly.


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Degree 90 products are also available. These products have a typical latency of 1—2 months. These geopotential coefficients may be used to compute geoid height, gravity anomalies, and changes in the distribution of mass on Earth's surface. The mission will track gravitational changes in global sea levels, glaciers, and ice sheets, as well as large lake and river water levels, and soil moisture.


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  8. From Wikipedia, the free encyclopedia. Play media. Spaceflight portal. National Space Science Data Center. Retrieved 17 August Gunter's Space Page. Retrieved 10 December March Retrieved 11 December Retrieved 23 May Retrieved 31 October Retrieved 11 March Retrieved 13 February University of Texas.