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Ground transient electromagnetic method inversion method and device based on emission current full waveform

A technology of transient electromagnetic method and emission current, which is applied in the direction of measuring device, electric/magnetic exploration, radio wave measurement system, etc., can solve the constraints of data processing and interpretation accuracy, strong eddy current signal, data processing method is not applicable to late data, etc. problems, to achieve the effect of perfecting the design of instrument parameters and improving the accuracy of interpretation

Pending Publication Date: 2022-07-22
CHINA UNIV OF GEOSCIENCES (WUHAN)
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Problems solved by technology

[0003] At present, the ground transient electromagnetic method data processing software adopts the oblique step current waveform, which only considers the influence of the off time, but ignores the influence of the stable time, the on time and the number of cycles in the emission current waveform.
However, in the background of high-conductivity exploration, the eddy current signal generated with the current turn-on is strong and decays slowly. Even if the stabilization time is as long as tens of milliseconds, the eddy current signal may not be fully attenuated, and it will still partially offset the transient electromagnetic response after turn-off. especially obvious
Therefore, the data processing method of the ground transient electromagnetic method that only considers the influence of the off time is not suitable for the late data, and restricts the further improvement of the accuracy of data processing and interpretation

Method used

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  • Ground transient electromagnetic method inversion method and device based on emission current full waveform
  • Ground transient electromagnetic method inversion method and device based on emission current full waveform
  • Ground transient electromagnetic method inversion method and device based on emission current full waveform

Examples

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Embodiment 1

[0091] Example 1: Theoretical Model

[0092] The one-dimensional inversion objective function is constructed based on the Tikhonov regularization method, and the Gauss-Newton method is used to optimize it. Inversion objective function set as:

[0093]

[0094] In the formula, the first term is the fitting difference function between the observed data and the forward model response, the second term is the model regularization function, || · || represents l 2 norm. where d obs is the observation data vector; d pre is the response vector of the forward model corresponding to the model parameter vector m, namely F(m), where F represents the one-dimensional forward model function of the transient electromagnetic method; W d is the data weighting matrix, here is a diagonal matrix, W dThe element of is the reciprocal of the standard deviation of the observed data; α is the regularization factor; m * For the reference model, prior information is included. W m is the model...

Embodiment 2

[0129] Example 2: Field observation data

[0130] Step S1: input the observation data and working parameters of the transient electromagnetic method;

[0131]The observation data collection site is a tidal flat in the East China Sea. This area is in an alternating land and sea environment. The shallow stratum is generally saturated with seawater, and the resistivity is only 0.1 to 0.8 Ωm. The resistivity of the deep stratum increases slightly. The observed data is the step response of the magnetic induction intensity of a measuring point, which is collected by a superconducting quantum interferometer (SQUID) produced by Crone Instruments in Canada. The emission source is a rectangular loop with a side length of 400m×200m, the loop center coordinate is (0,0,0)m, and the measurement point coordinate is (-100,0,0)m. The emission current is 25A; the basic waveform of the emission current is a bipolar current waveform (50% duty cycle) with a basic frequency of 0.833333Hz used by t...

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Abstract

The invention provides a ground transient electromagnetic method inversion method and device based on emission current full waveforms, and the method comprises the following steps: constructing a one-dimensional inversion target function based on a Tikhonov regularization mode, carrying out the optimization of the inversion target function through employing a Gaussian Newton method, and outputting a final inversion model. In a process of optimizing an inversion objective function, an emission current basic waveform used for one-dimensional inversion of a ground transient electromagnetic method is expanded from a slope step waveform to an emission current full waveform containing starting time, stabilization time, turn-off time and a duty ratio, and a cycle number parameter is included in the emission current basic waveform. The strategy is not only helpful for improving the interpretation precision of data processing, but also helpful for perfecting the design of instrument parameters.

Description

technical field [0001] The invention relates to the field of geophysical detection, in particular to a ground transient electromagnetic method inversion method and device based on the full waveform of an emission current. Background technique [0002] The ground transient electromagnetic method mostly adopts the "bipolar" emission current waveform, that is, both positive and negative power supply in one emission cycle. like figure 1 As shown, both positive and negative supply half-cycles include current turn-on, settling, and turn-off phases, as well as a measurement phase. In the "bipolar" waveform, eddy currents are induced in the underground medium each time the emission current is turned on and turned off, and the eddy currents generated by the previous turn-on or turn-off of the emission current will inevitably partially offset the eddy currents generated by the next turn-off or turn-on. . Affected by the above phenomenon, there are differences in the magnitudes of t...

Claims

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Application Information

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IPC IPC(8): G01V3/38G01V3/40G01V3/08
CPCG01V3/38G01V3/40G01V3/08Y02A90/30
Inventor 李建慧胡祥云
Owner CHINA UNIV OF GEOSCIENCES (WUHAN)
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