Testing Our Understanding of Short Period Mass Variation Processes with
Future Earth Gravity Missions
Abstract
A new mission called GRACE Follow-On is now flying to continue the
measurements started by the GRACE mission, and to test a laser
interferometry system for making more accurate measurements of the
satellite separation. In this paper we discuss the potential scientific
benefit of strongly reducing the acceleration noise in a Next Generation
Gravity Mission (NGGM), compared with that for GRACE and for GRACE
Follow-On. A useful way of comparing the scientific benefits is from the
view point of how well they can be used to test different procedures for
estimating the changes in the geopotential based on sources of
geophysical information other than satellite gravity results. In
particular, changes in hydrology, the atmospheric density, and ocean
conditions can make large and very non-uniform changes in the
geopotential in short periods of time. To make the discussion as simple
as possible, we consider mainly the variations in the geopotential at
altitude along the satellite orbit for different ground tracks. For the
NGGM, we initially assume laser interferometry between the two
satellites but the same satellite acceleration noise level as for the
GRACE-Follow-On mission. Then the total measurement noise level at long
and medium wavelengths would be only moderately below the geopotential
variation estimation uncertainty. However, if the acceleration noise
level were sharply reduced by replacing the GRACE-type accelerometers by
simplified gravitational reference sensors, it appears that considerably
improved tests of different procedures for geophysical estimates of the
geopotential variations could be made.