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Science Measurement Objectives
The following table presents a concise summary of exactly what measurements GRACE will obtain and the instruments that are used to obtain them, as well as how many spacecraft are involved in each measurement.
| Science Application
| Measurement
| Instrument
| # of spacecraft needed for measurements
|
| Earth Gravity Field |
Inter-Satellite Range Change Link |
K-Band Microwave |
2 |
| Earth Gravity Field Accelerations |
Non-Gravitational |
Accelerometer |
2 |
| Earth Gravity Field |
Satellite Orbits |
Black Jack GPS Receiver |
2 |
| Atmospheric Occultation |
GPS-to-GRACE Phase Change |
Black Jack GPS Receiver |
1 |
This science data in conjunction with ancillary data, will then be used to gain estimates of spherical harmonic coefficients of the Earth's gravitational potential.These coefficients are necessary to construct the 30-day maps of gravitational potential that will be the end product from the primary GRACE measurements.
Gravity Measurement Error
| Inter-satellite Range Measurement: |
< 4 µm @ twice/rev
< 10 µm total @ 0.1 to 0.0001 Hz |
| Non-Gravitational Acceleration Measurement:
|
< 10 -10 m/s2 noise (+1/f)
< 4 x 10 -12 m/s2 tones. |
| Precision Orbit Measurement: |
5 cm absolute
< 0.2 mm, relative in plane |
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