Reseach On New Method Of Downward Continuation And Envelope Analysis Of Potential Field

Potential field data processing is an important process for comprehensive interpretation of Geology and Geophysics.It can be used to study deep geological structures,explore and develop mineral resources,predict and control disasters,etc.,so as to ensure the safety of people’s lives and property and serve the sustainable development of the country and society.In recent years,with the increasing demand for the accuracy and precision of the potential field data,the potential field data processing method with high accuracy,strong stability and anti-interference ability has become an important research topic.The potential field downward continuation(DWC)method can calculate the abnormal field below the observation plane and display the characteristics of the deep field source.However,the downward continuation problem is incomplete and ill-posed theoretically.In order to reduce the incompleteness and ill-posed nature of downward continuation of potential field,the anthor constructs a set of algorithms of downward continuation quasi-neural network based on the idea of neural network to calculate the accurate downward continuation of gravity anomaly.The quasi-neural network is composed of several neuron layers connected in series,and each extension calculation can be regarded as the transfer process of the neural network.Before the data transfer,the minimum curvature method is used to expand the edge of the data to reduce the Gibbs effect caused by the calculation error of the edge data.For the downward continuation operator,the generalized inversion technique is used to solve the generalized inverse of the operator,and the stability of the downward continuation operator is increased.Similar to the functions of threshold and activation function of traditional neural network,the threshold and activation function in downward continuation quasi-neural network are defined,so that each layer of neurons can analyze the input data,judge whether the result of downward continuation is close to the field source,and determine the optimal control parameters for downward continuation calculation of this layer.The singularity statistics and singularity probability of the signal are defined mathematically to characterize the singularity of the extension result.The minimum curvature method is used to correct the continuation data with large singularity to weaken the influence of the current depth random disturbance.Numerical simulation experiments show that this method can effectively reduce the interference of shallow random field source to deep field source and obtain more accurate information of deep field source.Good results have been achieved in the application of gravity field processing in the QinghaiTibet Plateau,as well as in the detection and positioning of marine intrusion weights.The another content of this paper is using the envelope mode of geomagnetic field to process geomagnetic anomaly data.In order to obtain information about the magnetic strength distribution of crustal rocks from the ground magnetic field observation data,Hilbert transform is performed on the ground magnetic field observation data to obtain the envelope mode magnetic field reflecting the magnetic changes of crustal rocks and apply it to the relevant crustal structure positioning.According to the characteristics of magnetic anomaly field,three different ways can be used,namely,full envelope,positive envelope and negative envelope.Since the magnetization directions of the geomagnetic fields in the southern hemisphere and the northern hemisphere are opposite,the full envelope or positive envelope method is used for the northern hemisphere,and the negative envelope method is used for the southern hemisphere.Different calculation methods are used for the northern and southern hemispheres respectively to achieve the application effect of the envelope mode magnetic field processing.The experiment using EMAG2 global satellite magnetic anomaly field data shows that the envelope mode magnetic field strong anomaly coincides with the spatial distribution of craton tectonic units with strong crustal magnetism,which verifies the application effect of envelope mode magnetic field processing.The magnetic field analysis method of geomagnetic field envelope mode can provide images that are positively correlated with the magnetic properties of crustal rocks,and can be directly compared with gravity,wave velocity,resistivity and other information in the comprehensive study of crustal structure.