| The GOCE gravity gradient data is conducted on satellite orbit altitude, in order to getgravity gradient reduction value on the fixed datum point, the GOCE gravity gradient datashould be reducted to the same basis reference. This paper focus on the satellite gravitygradient space propagation characteristics, the effects of topography and atmospheric on thesatellite gravity gradient, the downward continuation methods and the grid transformation ofgravity gradient, which are the main steps in the process of reduction. The main researchresults are as follows:1) We design and implement the simulation software of satellite gravity gradient inmultiple reference frame in C++, and analysis the transmission characteristics of gravitygradient in the spectral domain. The results show that along with the increase of observationaltitude, the medium-high frequency parts in gravity gradient are sharply decayed, while thelow frequency part recession relatively slowly.2) Based on spherical harmonic function, we deduce the formula of the terrain andatmospheric effects to the GOCE gravity gradient data, and respectively simulate the terrainand atmospheric effects in Asian region with ETOPO30DEM data. The experimental resultsshow that the terrain effects is about-5.164~6.693E and the atmospheric effects is about-3.8~3.0E.3) We analysis several commonly used gravity gradient downward continuation methodsand the grid transformation methods, numerical test shows that: in the process of downwardcontinuation, the least squares method in frequency domain has the highest accuracy, behindwhich is the Taylor series method; On the grid transformation, the Shepard method has arelatively high accuracy, while the weighted average method is relatively low.4) Finally, we use GRACE data in nearly a decade to calculate the gravity gradient onGOCE orbit (250km altitude) in Japan region, and the time-series gravity gradient resultsreflects seismogenic process of Japan Mw9.0earthquake. |
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