Space-borne gravimetry: determination of the time variable gravity field
The gravity field of the Earth can be divided into a dominant quasi-static part and several relatively small but significant temporal constituents. Important examples of temporal sources are ocean tides, atmospheric pressure variations, and geophysical signals like those of continental hydrology and ocean bottom pressure variations predicted by the ECCO ocean model. Space-borne gravimetry, such as by the GRACE system, aims at observing including those induced by continental hydrology. A case study, based on a simulated gravity field retrieval for a 1-year GRACE-type mission, has been conducted to analyze the separability of continental hydrology from other temporal gravity sources.
It has been investigated how typical differences between recent ocean tide models and between global atmospheric pressure variation maps affect the observations (low-low satellite-to-satellite range-rate tracking (SST) and orbital positions from GPS high-low SST) and retrieved gravity field spherical harmonic expansions. In addition, the aliasing of signals predicted by the ECCO model and the effect of low-low SST observation noise and uncertainties in the recovered orbital positions has been analyzed.
It is concluded that large scale features of continental hydrology can be observed by a GRACE-type mission, provided that the low-low SST observations have a precision at the level of 1 µm/s at 1 Hz, and when great care is taken with the gravity field recovery approach.
Key wordslow-low satellite-to-satellite tracking temporal gravity hydrology atmosphere tides ocean models
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