Application Of Direct Analytical Signal Method Based On Two-dimensional Hilbert Transform In Gravity Magnetic Field

Gravity and magnetic exploration is an economic,fast and large-area geophysical exploration method with good lateral resolution.The boundary(edge)characteristics of underground geological bodies or structures can be effectively extracted by gravity and magnetic anomaly processing.A series of gravity and magnetic field edge recognition and enhancement methods based on gravity and magnetic field gradient or high-order derivative have been developed at home and abroad,such as total gradient,horizontal total gradient,theta diagram,tilt angle method,etc.these methods can achieve good results in gravity and magnetic data processing with less interference.However,for the airborne gravity and magnetic data,the strip interference phenomenon often exists due to the sharp undulation of terrain and the large difference between adjacent lines,which can not be completely eliminated by leveling and filtering.In this case,the application of conventional boundary recognition methods based on derivative or gradient calculation will be limited.In order to meet the needs of airborne gravity and magnetic data processing,which is not suitable for the conventional gravity and magnetic boundary recognition method,this paper studies the Hilbert transform technology and the direct analytic signal method based on Hilbert transform,and constructs four methods(direct analytic signal mode,horizontal component mode,improved theta diagram and improved tilt angle method)applied to the boundary enhancement and recognition of gravity and magnetic potential field.The gravity and magnetic single model and combined model are constructed,and the model test and comparative analysis are carried out.The experimental results show that the direct analytic signal method based on Hilbert transform can avoid the influence of noise amplification because it avoids the gradient or derivative calculation compared with the conventional method based on derivative,and has strong anti noise ability,stable calculation and better model boundary description ability.The method is applied to the gravity and magnetic anomaly processing in the southwest sub basin of the South China Sea.The characteristics of gravity and magnetic anomaly in the study area are obtained,such as the direct analytical signal mode,the horizontal component mode,the improved theta map,the improved tilt angle,etc The inner islands and reefs of Nansha block are the main geological structures.When there is remanence in the magnetic anomaly,the results of direct analytical signal mode,magnetic modulus and total gradient mode are compared and analyzed.It is concluded that the effect of direct analytical signal mode is better than the other two methods.