Date of Award
Doctor of Philosophy (PhD)
Aerospace Engineering Sciences
R. Steven Nerem
The Gravity Recovery and Climate Experiment (GRACE) mission has demonstrated the ability to quantify global mass variations at large spatial scales with monthly to sub-monthly temporal resolution. It is expected that future missions will take advantage of improved technologies by flying drag-free and performing the satellite-to-satellite ranging with a laser interferometer. With these improvements, errors due to under-sampling geophysical signals will be the limiting error source. In an effort to reduce the level of these temporal aliasing errors, we suggest the addition of a second pair of satellites. A Monte-Carlo analysis using numerical simulations is used to reduce the search space for finding an optimal architecture consisting of two satellite pairs. A search space originally consisting of fifteen variables is reduced to two variables with the utmost impact on mission performance: the repeat period of both satellite pairs (shown to be near-optimal when they are equal to each other), and the inclination of one of the satellite pairs (the other is assumed to be in a polar orbit). With appropriate assumptions, we find that an optimal architecture consists of a polar pair of satellites at 320 km coupled with a 290 km pair inclined at 72 degrees, both in 13-day repeating orbits. The option of estimating low resolution gravity fields at a high frequency is shown to further reduce temporal aliasing errors. Global and regional analyses are performed to quantify the expected scientific benefits of adding an optimally-placed second pair of satellites. Analysis using empirical orthogonal functions reveals that two satellite pairs determines annual and semi-annual mass variations in small basins which are undetected using one pair of satellites. Averaging kernels and spatiospectral localization are used to show error reductions ranging from 25% - 75% in determining mass variations over the year in 53 hydrological basins, 12 Greenland basins, and one ocean basin. A simulated earthquake signal is also shown to be detected with higher spatial resolution. Perhaps the largest benefit of having two satellites pairs is that the gravity solutions do not necessitate ad-hoc GRACE post-processing techniques of removing correlated errors and smoothing when studying signals to spatial resolution of ~330 km.
Wiese, David N., "Optimizing Two Pairs of GRACE-like Satellites for Recovering Temporal Gravity Variations" (2011). Aerospace Engineering Sciences Graduate Theses & Dissertations. 28.