Zhai Guojun

Comparisons of Three Inversion Approaches for Recovering Gravity Anomalies From Altimeter Data

One of the major applications of satellite altimetry is to recover gravity information. In this paper, three methods (i.e., analytical and numerical inversion of the stokes formula, and the inverse Vening Meinesz formula) for deriving gravity anomalies from altimeter data are developed and studied in detail. The three formulae are implemented using fast Fourier transform (FFT) technique. And a series of modified spherical 2D FFT formula for the computation of gravity anomaly have been proposed in this step. Then they are compared and tested using synthetic data from an ultra high degree geopotential model MOD99c to degree and order 1440. The stability of the three approaches is investigated using simulated data, and many numerical tests are done to quantify the feature of the three approaches. Finally, the three formulae are employed to compute gravity anomalies over the South China Sea using geoidal undulations and deflections from Seasat, Geosat, ERS-1 and TOPEX/POSEIDON (T/P) satellite altimetry. And the estimated gravity anomalies are compared to marine gravity data from shipboard measurements in the studied area.

A Modified Method for Recovering Bathymetry from Altimeter Data

At present, there exist two types of methods to recover the bathymetry from altimeter data, i.e. the deterministic method and the stochastic one. This paper first reviews the general principles of the two aforementioned methods in order to form the basis for the development of the new approach. Then, based on the theory of least-squares collocation, a modified statistical model for recovering bathymetry from altimeter data is proposed. The new model is used to compute the ocean depth in the South China Sea from altimetry-derived gravity anomalies. Finally the predicted depths are compared to the shipborne ones. The results show that the achievable agreement is very good. Taking into account the existence of errors in the shipborne depths, it can be believed that the relative error of altimetry-derived depths reaches the level of about 7%.