Point-mass sensitivity of gravimetric satellites
Robert Spero
Abstract
Frequency-domain expressions are found for gradiometer and satellite-to-satellite tracking measurements of a point source on the surface of the Earth. The maximum signal-to-noise ratio as a function of noise in the measurement apparatus is computed, and from that the minimum detectable point mass is inferred. A point mass of magnitude M3=100Gt gives a signal-to-noise ratio of 3 when a GOCE-like gradiometer passes directly over the mass. On the satellite-to-satellite tracking mission GRACE-FO M3=1.3Gt for the microwave instrument and M3=0.5Gt for the laser ranging interferometer. The sensitivity of future GRACE-like missions with different orbital parameters and improved accelerometer sensitivity is explored, and the optimum spacecraft separation for detecting point-like sources is found. The future-mission benefit of improving the accelerometer sensitivity for measurement of non-gravitational disturbances is shown by the resulting reduction of M3, to as small as 7 Mt for 500 km orbital altitude and optimized satellite separation of 900 km.