MULTIDIRECTIONAL AND MULTISCALE EDGE ANALYSIS OF POTENTIAL FIELD DATA

With the wide applications of aerogravity and aeromagnetic survey, the collection and analysis of gravity or magnetic data represents one of the convenientest and cheapest forms of large-scale geophysical exploration. Mapping the three-dimensional distribution of rock properties from potential field data is a difficult and arduous task. With the identification of sources of potential fields, we can get the map of worms or skeletonizations showing the three-dimension structure of shallow crust. We show a new directional wavelet transform and edges detection techniques of potential field maps and propose interpretation schemes for characterizing 3D sources. The strength of this new approach is the use of multidirectional and multiscale edges detection to the potential field data, and which leads to relations between the horizontal directional derivatives of geophysical field measurements at all heights, and the directional wavelet transform of the zero height field. The union of points with local maxima of each directional wavelet transform modulus was taken as the edges at each single-scale, and the points are better visualised and interpreted by converting them into polylines or strings, which formed worms or skeletonizations map. Other than methods of analytic signal or multiscale edges detection, directional edge information of sources of potential fields can be acquired with the method of multidirectional and multiscale edges detection, which are important for some kinds of applications. For example, the mineralization are controlled by the intersection of different directional structures at different spatial scale, and the structures include faults, discordant contacts, discontinuous stratigraphic sequence, boundary of magmatic body, thin sheets, and so on. For the evaluation of the availability and spatial precision of the approach, we contrasted the gravity worms map with geological map, geochemical anomalies map and ASTER remote sensing image at several area. The tests show the technique are effectiveness to geological interpretation of potential field maps and helpful to constraints on the three-dimensional geology. The approach will increase the chance of discovery of mineral deposits, and has been successfully applied to mineral exploration of hydrothermal deposits at Jiangxi and Yunnan province, China.