Transient electromagnetic inversion method for sharp boundary model

Abstract

The invention discloses a transient electromagnetic inversion method for a sharp boundary model. The method comprises the following steps: secondary field data observed via a transient electromagnetic method is input, inversion parameters are input and an inversion initial model is built; a mismatch general function between observed data and forward modeling theory data is built, a minimum gradient support general function used for restraining resistivity change is built, an inversion object function is built via the mismatch general function and the minimum gradient support general function, the initial model is used as initial conditions, a Gauss-Newton method is used for solving resistivity corresponding to a minimum target function, and an inversion result is obtained. Via the inversion method, a resolution of a underground resistivity abrupt change surface, a defect of unclear electrical interface reflection in an Occam inversion algorithm can be compensated, characteristics of stability and simplicity of the Occam inversion algorithm are kept in the transient electromagnetic inversion method, and the transient electromagnetic inversion method is of great significance for transient electromagnetic data inversion and late stage data interpretation.

Description

technical field [0001] The invention relates to the technical field of geophysical detection, in particular to a transient electromagnetic inversion method of a sharp boundary model. Background technique [0002] As a powerful means of geophysical exploration, transient electromagnetic method can solve various geophysical problems such as mineral exploration, energy, engineering, hydrology, environmental geological survey, and archaeological exploration. It uses step waves or other pulse currents to emit a pulsed magnetic field underground, and the underground conductive geological body generates an induced eddy current under the excitation of the primary field, and then stimulates a secondary magnetic field. When the emission current is turned off, the primary field disappears, and the subsurface eddy current decays with time, and its decay time is related to the electrical parameters (volume, structure, resistivity, buried depth) of the conductive geological body. By obse...

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Problems solved by technology

[0005] The invention provides a transient electromagnetic inversion method of a sharp boundary model, which is used to solve the unstable inversion of the Marquardt method, the Occam method to smooth the change of the earth resistivity as much as possible, and the layered boundary resolution of the sudden change of the resistivity. However, it is impossible to accurately describe the layered structure of the earth and the mixed use of the above two methods is not convenient enough in practical engineering applications.

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