Constrained inversion method and application effect of TEM data of fixed source loop device

In order to eliminate the obvious framing effect after the TEM fixed source loop device increases the receiving area, to improve the delamination ability of TEM to enhance the fine resolution for different electrical strata, the regularization inversion method with constraint is adopted. In the inversion algorithm, the Lagrange factor is adjusted adaptively by CMD regularization factor. In order to ensure the efficiency, stability and convergence of the results of the inversion process, the thickness of each layer of the inversion model is discretized according to the equal logarithmic interval, and the ill conditioned property of the matrix equation is reduced. At the same time, a feasible upper and lower limit is used for the inversion of the resistivity value, so that the extreme value or the error value can not appear in the results of the iteration, and the multi solution of the inversion is reduced. Through the calculation of the multi-layer theoretical model, the correctness and reliability of the constrained inversion algorithm are proved. It is used in the inversion calculation of the measured data of the transient electromagnetic method. The vertical distribution of the inversion resistivity is consistent with the data of the known stratum, and the abnormal area is verified by drilling, and the result is reliable.