On the determination of geopotential differences from satellite-to-satellite tracking

The Earth's gravitational potential field can be obtained directly from low-low satellite-to-satellite tracking using range-rates and/or velocity vector differences. There axe some possible advantages to measuring potential instead of acceleration or gradients of acceleration, as alternatively proposed. For example, direct geoid modeling in local areas without recourse to Stokes's integral (but still Poisson's integral to account for downward continuation). The usual measurement model relates the in situ geopotential difference to the range-rate between two satellites. This model neglects the effect of Earth's rotation, which is on the order of 0.1 kgal*m for polar-orbiting satellites. In this paper an analytic expression is derived for that effect. It is shown that the potential rotation effect can be determined in situ only from velocity and position vector measurements, which is possible using GPS baseline measurements. Applications to two upcoming satellite mission, GRACE and COSMIC are discussed.