Apply Wavelet Multi-scale Analysis To Separate The Marine Gravity Field

Research on regional geological require large amounts of geophysicalinformation, Among the several geophysical exploration methods, gravity prospectingare widely used for its features of accessible, fast, strong applicability. Gravity data isalso the most complete geophysical data, so gravity data often plays a fundamentalrole in the research. In the research on the geological structure of large-scale and greatdepth, gravity data is used as the main research data, gravity field data inversionprovide the information what other geophysical data can not provide.Gravity anomaly reflects the distribution of the residual mass underground whichthe uneven distribution of the underground material density that caused by geologicalstructure or mineral distribution. Do the inversion of gravity anomaly data can get theinformation of underground geological structure, but the gravity anomaly is acomprehensive reflection of the residual quality underground, If we want to get amore specific and detailed information of the structure, we must divide the gravityanomaly caused by different geological structure before we do the inversion, then weget the a more specific information of the structure. Traditional dichotomy is dividingthe gravity anomaly into regional anomaly caused by large-scale structure and localanomaly caused by small-scale structure or geologic body. Traditional separationmethods include high-order derivation, analytic continuation, trend analysis and so on,These methods divide the gravity anomaly in the spatial domain. Actually theregenerally exist an obvious difference between regional anomaly and local anomaly,we can divide the gravity anomaly in the frequency domain based on the frequencydifference. The wavelet transform is a quite perfect tool to realize conversion betweenspatial domain and frequency domain, It has the advantage of multi-scale analysis,and it can be quickly implemented by combining the Mallat algorithm and filter banks.The multi-scale decomposition of wavelet transform is also more consistent with themultiple solutions of the inverse problem. So many advantages described above makethe wavelet transform can effectively divide the gravity anomaly theoretically.This article is about the research on the separation of the gravity anomaly field by wavelet multi-scale analysis technique, and through the actual marine gravity dataprocessing test to verify the practical application effect of this technique, and dostructural analysis of the separation results combined with other geophysical data.The main contents of the paper and steps are: First, study the basic features andprinciples of gravitational potential field and gravity anomalies, study mathematicalprinciples of high-order derivation and analytic continuation, and design thecorresponding program, then study to understand the principles of wavelet multi-scaleanalysis and design its program with Matlab, study and propose the principle ofselecting the mother wavelet. Then establish gravity anomaly data model and handlethe data respectively by high-order derivation, analytic continuation and waveletmulti-scale analysis, compare the advantages and disadvantages of three methods, trydifferent mother wavelets and different decomposition levels to verify the principle ofselecting the mother wavelet and select the most realistic decomposition level. At last,respectively select the marine gravity anomaly satellite data of part of South ChinaSea and East China Sea to do the wavelet multi-scale analysis test, and give thecorresponding structural analysis of the separation results combined with correlationanalysis and topographical data.The results of research shows that wavelet analysis can divide the gravityanomaly quickly, efficiently, and accurately, it has significant advantages comparewith high-order derivation and analytic continuation. The actual marine gravityanomaly data processing results show that， the fourth-order approximation ofWavelet multi-scale analysis primarily caused by the ups and downs of Moho.，andthe fourth-order details are mainly reflects the ups and downs of the depositionsubstrate surface.