The Determination Of Regional Geoid With Satellite Gravity And Its Applications In Geophysical Interpretation

In this paper, three case studies in the area of Hunan Province about the applications of satellite gravity in the determination of the geoid and the geophysical interpretation are presented in detail, due to the uneven distributions of the terrestrial gravimetric data and the dramatically development of the satellite gravimetric data in terms of accuracy and resolution. Meanwhile, the corresponding principles and methods are introduced. The main contents and conclusions are listed as follows:1. The accuracies of the Geoids computed from several Geopotential Models (EGM08, EGM96, GGM02, etc) are compared. The analysis of their degree variances is presented firstly. In order to generating the accuracies of the long-medium and short medium components of the models, the Geoid Undulations computed by the models up to degree 120 and 360 are evaluated combing with the GPS Leveling Data in the research area. Considering the effect of the topography on the Geoid and the deficiency of the observed gravity data, the research area is divided into the flat part and the mountainous part roughly, and then the model values on the reference points are compared in each part. Finally, a Least Square Fitting (LSF) is used to correct and modify the model values. The Geoid computed from EGM08 is demonstrated to be the most precise one in the research area according to the results.2. A new V18.1 Satellte Gravity Anomalies (SGA) which was recently published online by Sandwell D T, et al is used as the regional gravity data to compute the geoid of the research area with the "Remove-Restore" technique in the case of no observed terrestrial gravity data. The resolution of the geoid is 1'×1' which is the same as that of the SGA, the EGM96 and EGM08 global geopotential models up to degree and order of 360 are chosen to be the reference field respectively. The main purpose of this part is to discuss the accuracy of the geoid computed by the SGA and the results are showed as follows. The gravimetric geoid derived from the SGA can achieve to an accuracy of about 0.05m. It means that, in the future geoid modeling, the SGA can be used to combine with the terriestral gravity or to be a substitute one in the area with no terriestral data.3. The satellite gravity mentioned in Part 2 is used to compute the gravimetric geoid (GG) and calculated Bouguer gravity anomalies (CBGA) over the research area. Both of them are synthetically analyzed because of their different sensitivities to the signals caused by deep and shallow anomalous sources. Moreover, the GG is separated into several residual gravimetric geoid (RGG) maps which reveal the anomalous features in different depth, by removing the long wavelength geoid features. In order to generating residual gravity anomalies (RGA) and apparent density anomalies (ADA) corresponding to strata of different depth, a cutting method for the potential field separation and apparent density inversion method are applied to process the CBGA. Then geophysical interpretation of the research area based on these data sets and other geophysical results is presented. The feasibility of satellite gravity in geophysical interpretation is demonstrated by the final results.