Physics
Scientific paper
Dec 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufm.g32a0726t&link_type=abstract
American Geophysical Union, Fall Meeting 2003, abstract #G32A-0726
Physics
1214 Geopotential Theory And Determination, 1227 Planetary Geodesy And Gravity (5420, 5714, 6019), 1243 Space Geodetic Surveys
Scientific paper
The GRACE mission, which was launched in March of 2002, should have orbit coverage nominally sufficient to estimate the gravity field as a piecewise mean every 30 days with a spatial resolution on the order of 400 km. Due to the nature of this orbital the orbit sampling, short period mass variability will not be completely observable. This short period variability can alias into the longer period gravity estimates at a variety of spatial scales, affecting the accuracy of the gravity results. Perfect knowledge of the short period (primarily daily) mass variability of the Earth would be required to remove the aliasing effects completely. Since the true variability is not known, simulations are used to estimate the aliasing error that may be present in the GRACE gravity estimates. Contemporary atmospheric, ocean, and hydrology models are used to approximate the variability present in the Earth's dynamical system. Different combinations of these models will be used to construct an estimate of the unmodeled signal present during GRACE gravity recovery. The aliasing error determined from these simulations will be described. GRACE data processing has adopted an atmosphere-ocean de-aliasing (AOD) model provided by GeoForschungsZentrum Potsdam (GFZ). The AOD product is based on six hour global data from the ECMWF combined with a barotropic ocean model. The time series of geopotential coefficients from this product is used in order to remove some of the short period variability due to the atmosphere and oceans. At a minimum, the impact of using an AOD model will need to show no degradation in the orbit determination, measurement residuals, or covariance of the gravity fields. We will discuss the implementation of the AOD model in the GRACE data processing and compare the resulting gravity estimates with gravity estimates that did not use an AOD model. Furthermore, the GRACE solution perturbation due to using or not using the AOD model will be contrasted with corresponding aliasing simulations.
Bettadpur S. V.
Tapley Byron D.
Thompson Paul F.
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