Study On 1D Inversion Of Multi-source Ground-airborne Transient Electromagnetic Method

Since the beginning of "13th Five-Year Plan",with the planning and implementation of "one belt one road" strategy,China's mineral resources reserve task is arduous.And the environments of mineral resources survey is the harsh and dangerous,such as terrain rugged desert,mountain,forest and lake and other areas.As the surface environment is complex and bad,it is difficult and dangerous to carry out ground geophysical exploration in the above areas.It increases the time,manpower and material cost of mineral survey.Therefore,there is an urgent desire for a practical production and efficient and accurate geophysical methods.The ground-airborne transient electromagnetic method combines the principle and observation mode of ground and air transient electromagnetic,places the emission source on the surface,and uses the aircraft(eg UAV,rotorcraft,or airship,etc.)to receive the response signal in the air.Therefore,the ground-airborne transient electromagnetic method also has the advantages of large sounding depth of the ground device,high signal noise advantage and high efficiency of aviation equipment acquisition.These advantages also reflect the method from the side to adapt to the desert,lakes,high altitude mountains and other areas of great difficulty.At present,the ground-airborne transient electromagnetic method has been applied in volcanic structure investigation,metal mineral investigation and water resources investigation.However,the existing method is based on the interpretation of the data of the large loop source and the long wire source device,and the interpretation result are influenced by terrain undulating and flight height.In addition,in the way of excitation,the present study focuses on a single radiation source,ignoring the multi-radiation field source in the exploration depth and signal to noise ratio advantage.Therefore,it is necessary to study the data interpretation method applicable to the multi-radiation field source.Geophysical data interpretation of the final research direction is to carry out inversion calculation,and one-dimensional inversion is the basis of three-dimensional inversion,so this paper for multi-radiation field source air transient electromagnetic method of one-dimensional inversion problem to discuss with the work of the study.Firstly,solve the problem of the ground-airborne transient electromagnetic forward modeling.The paper on the basis of electric dipole source established the frequency domain response expression of the single-source in the air in the case of the homogeneous earth and multi-layered earth by the idea of superposition of subdivision.Then we on the basis of single-source established the frequency domain response expression of the multi-source in the air in the case of the homogeneous earth and multi-layered earth by the idea of superposition of subdivision.And we realized the calculation of transient filed of the ground-airborne transient electromagnetic by the sine or cosine transform.Secondly,on the basis of the principle of Occam inversion studied on one-dimensional inversion of multi-source ground-airborne transient electromagnetic.First of all,the important problem is the construction of objective function,and the objective function is constituted by the misfit and model roughness by introducing the Lagrange multiplier.The second,the problem of the construction of the sensitivity matrix is solved.Its elements are composed of first order partial derivatives,so the differential form is replaced by the differential form.The last,the linear search method is used to obtain the Lagrange multiplier,and the model parameters and the corresponding fitting difference and roughness are different for the different Lagrange multipliers.Therefore,in the calculation process we have to scan the Lagrange multiplier,and calculate the fitting difference and roughness of the model at this time.When the Lagrange multiplier is equal to a certain value,the fitting error of the computational model reaches the calculation accuracy and the roughness is minimized,and the Lagrange multiplier is the value we need.The research work of the paper mainly focuses on the above two parts,which enriches the interpretation system of the ground-airborne transient electromagnetic method,and studies the one-dimensional inversion of multi-source ground-airborne transient electromagnetic,which provides the basis for the final realization of three-dimensional inversion.