Pre-processing And Analysis Of Gravity Measurements On Islands

The dissertation was dedicated to the theoretical and analytical aspects of the preprocessingof gravimetric observations over ocean islands, which covers issues on solid Earth tidecorrection, ocean loading tide correction, vertical gravity gradient correction, zero-point shiftingcorrection and the effect of the linear scale factor of the LCR-G gravimeter on segment gravitydifference and observation accuracy.In the analysis of the solid Earth tide correction, the mechanism of the tide generating forcewas discussed at first, and then the effect of the theoretical formula of solid Earth tide ongravimetry was analyzed, where the selection of the solid tide factor by region was illustrated,and finally it was proposed that, with the increasing of solid Earth tide observatory, the solidEarth tide correction for gravimetry should be computed regionally using the tide factor fromactual measurements.In dealing with the computation of ocean tide correction, three ocean tide models wereintroduced according to the ocean loading tide theory and corresponding formulae, and theamplitudes and phases of the principle tide wave of the three ocean tide models. Finally based onthe analysis of the effect of the oceanic loading tide corrections for gravimetric observations ofthe12littoral gravity benchmarks on observation accuracy, the author thought it is necessary toestablish an ocean tide model suitable for China.In the analysis of vertical gravity gradient correction, the vertical gradient as well as itsabnormal points of normal gravity was studied, and then the nonlinearity of vertical gravitygradient and the observation accuracy using relative gravimeters were discussed. From thediscussions it was proposed that vertical gravity gradient measurement should be implemented aslong as possible in the high precision gravimetry over ocean islands so as to improve theaccuracy of gravity measurements.In the derivation of the zero-point shifting correction, the necessity of the static anddynamic experiment for the performance test of gravimeters was discussed, and it was illustratedthat for the computation of the zero-point shifting correction in the high-precision gravimetryover ocean islands using the observing method of point-by-point advancing with round-tripsymmetry, the mixed zero-point shifting rate can help reduce the effect of errors on relativegravimetry more effectively.At the end of the dissertation, the effect of the regional evaluation of the linear scale factorof the LCR-G gravimeter on the segment gravity difference was analyzed. To reduce the effect ofthe extrapolation of the scale factor on the preprocessing of gravimetric observations over oceanislands, the method for the calibration of the linear scale factor of the LCR-G gravimeter usingshort baselines as well as the measurement requirements were proposed.