Study On The Normalized Total Gradient Method Of The Potential Field Based On Stable Downward Continuation

Data processing is a key part of geological interpretation of gravity and magnetic data.Normalized total gradient method is a common method for potential field data processing,which can quickly reverse the location information of the geological body without any geological constraints.However,this method uses the ill posed downward continuation calculation,and the unreasonable extension model is easy to lead to the poor stability of the calculation results or the ability of abnormal resolution.At the same time,this method still has the problem of poor ability to identify the deep field source information,and the low accuracy of the geological body shape such as dykes and steps.In order to solve the ill-posed problem of downward continuation,In recent years,the advantages of iterative methods in improving continuation computational stability and computational accuracy have attracted attention.In this paper,firstly,three kinds of computational modes,integral iterative method,Taylor series iteration method and Compensation downward continuation method,are deeply compared.The results show that the iterative formulas of different iterative methods have strong similarities,only the selection of initial filter operators is different,but the rationality of the selection directly determines the application effect of the iterative method.Subsequently,we propose the regularization and iteration method in the wavenumber domain for downward continuation of potential field.The method is based on the systematic study of four kinds of downward continuation regularization methods,and we choose the most stable regularization method combined with iterative method.The contrast analysis results of the filtering characteristics of different downward continuation methods show that the regularization iteration method has obvious advantages in terms of calculation stability and calculation accuracy.Meanwhile,this method still has the advantages of strong amplitude preservation and small influence of iterations.The results were confirmed both in model tests and actual aeromagnetic data processing.In this paper,the generalized normalized gradient is used to identify the unsatisfactory effect of geologic bodies such as steps and veins.The power average function is introduced to normalize the problem;In view of the problem that the normalized total gradient method can not identify the deep field source,the normalized total gradient is discretized.At the same time,the iterative method is used to calculate the downward continuation of the normalized total gradient,and a discrete normalized total gradient method based on power mean is proposed.The model test shows that this method can not only identify the location information of the stacked field source effectively,but also judge the geometry of the geological body according to the best power number.The case application shows that the normalized total gradient method based on power mean has higher inversion accuracy and stronger actual data interpretation ability compared with the conventional normalized total gradient method.