| Gravity and magnetic exploration are two important branches of geophysical methods,which are suitable for large area exploration.They have the advantages of high efficiency,low cost,less destructive to the detection area,and more environmental protection.At present,they are widely used in mineral resources exploration,geological structure investigation,and crustal stability analysis and so on.The theoretical basis of gravity and magnetic exploration is to study and explain the difference between density and magnetism by measuring the gravity and magnetic field of the underground field source.Compared with other geophysical exploration methods,these two methods have more abundant regional geological information.In addition,they have obvious anomaly response to the deep large geological structure.Potential field data processing is the basis of interpretation and analysis of underground geological bodies through gravity and magnetic data.The edge detection of geological bodies is a very important link in the process of processing and interpretation,which can effectively determine the edge range of field source.Thus,the geometric characteristics of geological bodies are further analyzed and the anomaly is fleetly delineated.In this paper,the conventional edge detection methods are studied systematically,the basic principles are grasped,and the advantages and disadvantages of each method in the application process are summarized.On the basis of the conventional method,the wavelet combined with power transform method is further proposed to improve shortcomings.The wavelet has the characteristics of multi-scale analysis to suppress noise,and the degree of edge convergence can be improved by power transformation.The technology of image recognition is deeply studied,and the theoretical basis of Canny operator,Laplacian of Gaussian(LoG)operator and Sobel operator is analyzed in detail.These operators are applied to extract edge position of the field source,and detection effect of each operator is compared and analyzed.The validity of the above two methods is verified by building forward modeling data and combining the measured gravity anomaly data and magnetic anomaly data.In order to further determine the horizontal position of underground target and determine its buried depth,this paper focuses on the normalized total horizontal derivative.As a fast imaging technique,the normalized total horizontal derivative has the advantages of high calculation speed and efficiency,and it can obtain the spatial position information of underground target qualitatively and semi-quantitatively without the information of geometric parameters and physical property constraints of geological body.In this paper,the theoretical basis of normalized total gradient is studied in detail,and the concrete calculation steps of this method are introduced.In order to obtain the horizontal position and burial depth of the underground target at the same time,the method is extended to the normalized total horizontal derivative method.According to the principle formula of the normalized total horizontal derivative method,the influence of harmonic mean on experimental results is discussed by using harmonic mean as normalization method.The level and depth position of the target are determined by calculating the maximum point of the anomaly data,and the application effect of the method is verified by combining the theoretical model and the practical data.Through the above research,the method of wavelet combined with power transformation and image processing technology are used to realize the accurate division of field source edge.According to the normalized total horizontal derivative method,the horizontal position of the anomaly body is further delineated,and the depth information is obtained at the same time.Combined with the model data and the measured data,the practicability and validity of the above methods have been verified,and good application results have been achieved,and the research aim of this paper has been achieved. |
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