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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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The GRACE mission is jointly implemented by NASA and DLR under
the NASA Earth System Science Pathfinder Program.

Last Modified: Tue Feb 10, 2004