A method for processing weak signals in electromagnetic wave CT

Abstract

This invention discloses a weak signal processing method for electromagnetic wave CT, solving the problem that electromagnetic wave attenuation leads to signal submersion in strong environmental noise when electromagnetic wave CT technology is used for long-span measurements or measurements in strata with high absorption coefficients. This enables the application of electromagnetic wave CT technology with borehole spacing exceeding 40m in strata with high absorption coefficients, reducing the number of boreholes along geological exploration routes by more than half, significantly reducing drilling costs and improving geological exploration efficiency. This invention has been tested in several confidential experiments on multiple subway lines, achieving good results. The application of this invention will have significant implications for improving the efficiency of urban underground space development and geological exploration in complex environments, as well as controlling construction costs.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic wave CT detection technology, and specifically relates to a method for processing weak electromagnetic wave CT signals in this field. Background Technology

[0002] Chinese invention patent application: A method for correcting low-frequency, long-span electromagnetic wave CT data (application number: 202111449625.2) discloses a method for correcting signals of long-span electromagnetic wave CT propagating through the ground surface. The method corrects the ground surface waves through three holes. The shortcoming is that it does not consider the case where the noise is much greater than the signal when the span is long, and the ground surface waves cannot be corrected in this case.

[0003] Chinese utility model patent: An electromagnetic wave CT data acquisition system (application number: 201821126289.1) discloses a system for automatically recording and acquiring probe data depth. The method is that the control module controls the cable take-up and take-up device to achieve automatic cable take-up and take-up, avoiding the large workload and instability of manual operation; the depth value is fed back by the visual detection device to achieve precise control of the probe depth. The shortcoming is that it does not consider the quality of the acquired data. If the data is a weak signal, then the acquired data cannot be effectively used.

[0004] Chinese invention patent application: A method and system for extracting transient weak electromagnetic signals (application number: 202210271050.8) discloses a method for extracting transient weak electromagnetic signals. However, electromagnetic wave CT is a non-transient electromagnetic signal, so the method disclosed in this patent is not applicable.

[0005] Chinese invention patent application: A method and system for detecting weak downhole signals (application number: 202210295329.X) discloses a method for detecting weak downhole signals while drilling. The method is to obtain the DFT amplitude spectrum of the weak downhole signal while drilling; and to use a dual-peak search algorithm to search for the frequency of the weak downhole signal while drilling. The drawback is that the DFT transformation needs to meet certain signal-to-noise ratio conditions. The greater the noise, the longer the acquisition time, which affects the operation efficiency. Summary of the Invention

[0006] The technical problem to be solved by this invention is to provide a weak signal processing method for electromagnetic wave CT, which does not require long-term data acquisition for spectrum analysis or accumulation, and can achieve weak signal extraction in strong noise environment without affecting work efficiency.

[0007] The present invention adopts the following technical solution:

[0008] An improved method for processing weak signals in electromagnetic wave CT includes the following steps:

[0009] Step 1: Select the depth range and distance interval to be measured by the receiving antenna according to the operation requirements. Use the receiving antenna to measure the noise along the fixed-interval depth points in the hole to obtain the noise curve that varies with depth. Divide the collected noise into amplitude and phase to obtain two sets of noise curves A1 and B1 that vary with depth.

[0010] Step 2: Place the transmitting antenna at the deepest point in another hole, turn on the power, and transmit electromagnetic wave signals. Use the receiving antenna to receive the signals again along the fixed-interval depth points in Step 1. Divide the received signals into amplitude and phase to obtain two sets of received signal curves C1 and D1 that vary with depth.

[0011] Step 3: If C1 / A1 is greater than 5, the signal-to-noise ratio is high enough and no processing is needed; otherwise, proceed to step 4.

[0012] Step 4: Place the receiving antenna at a certain depth point in the hole, and disable the transmitting antenna. Use the receiving antenna to collect the noise amplitude a1 and phase b1 at that depth point. Then, move the transmitting antenna in another hole according to the depth range measured by the receiving antenna. The receiving antenna collects the amplitude c1j and phase d1j of the received signal, where j = 1, 2, ..., M.

[0013] Step 5: Place the receiving antenna at another depth point in the hole, repeat step 4, and use the receiving antenna to collect the noise amplitude ai and phase bi at that depth point. Then, move the transmitting antenna in another hole according to the depth range measured by the receiving antenna, and collect the amplitude cij and phase dij of the received signal, where i = 1, 2, ..., N.

[0014] Step 6: Convert the amplitude and phase of the received signal and noise into real and imaginary parts, and subtract them at the same depth point to obtain the real and imaginary parts of the received signal after noise removal. Then convert them into amplitude and phase for subsequent imaging.

[0015] The beneficial effects of this invention are:

[0016] The method disclosed in this invention solves the problem of electromagnetic wave attenuation causing signals to be submerged in strong environmental noise when electromagnetic wave CT technology is used for long-span measurements or measurements in strata with high absorption coefficients. It enables the application of electromagnetic wave CT technology with borehole spacing exceeding 40m in strata with high absorption coefficients, reducing the number of boreholes along geological exploration routes by more than half, significantly lowering drilling costs and improving geological exploration efficiency. This invention has been tested in multiple confidential trials during the construction of several subway lines, including the Hangzhou Sanjianghui Demonstration Zone, the Chongqing Demonstration Zone, and Wuhan, achieving good results. The application of this invention will have significant implications for improving the efficiency of urban underground space development and geological exploration in complex environments, as well as controlling construction costs. Attached Figure Description

[0017] Figure 1 This is a flowchart illustrating the method of the present invention;

[0018] Figure 2 This is a schematic diagram of noise collection by the receiving antenna;

[0019] Figure 3 This is a schematic diagram of the receiving antenna collecting and receiving signals;

[0020] Figure 4 It is a noise amplitude curve of a certain measurement;

[0021] Figure 5 This is a noise phase curve graph from a certain measurement.

[0022] Figure 6 It is an amplitude curve of a certain received signal;

[0023] Figure 7 It is a phase curve diagram of a certain received signal;

[0024] Figure 8 This is a noise amplitude curve from another measurement;

[0025] Figure 9 This is an amplitude curve of another received signal;

[0026] Figure 10 This is a graph showing the processed weak signal. Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0028] This invention discloses a method for processing weak electromagnetic wave CT signals during transaperture electromagnetic wave CT operations, such as... Figure 1 As shown, it includes the following steps:

[0029] Step 1: Select the depth range and distance interval to be measured by the receiving antenna according to the job requirements, such as... Figure 2 As shown, noise is measured at fixed depth points in the hole using a receiving antenna, for example, at a point 1m apart, to obtain a noise curve that varies with depth. The collected noise is divided into amplitude and phase, resulting in two sets of noise curves A1 and B1 that vary with depth. If the collected noise is amplitude information, only one set of noise curves that varies with depth can be obtained.

[0030] Step 2, as follows Figure 3As shown, the transmitting antenna is placed at the deepest point in another hole, the power is turned on, and an electromagnetic wave signal is transmitted. The receiving antenna is used to receive the signal again along all the fixed-interval depth points in step 1. The received signal is divided into amplitude and phase to obtain two sets of received signal curves C1 and D1 that vary with depth.

[0031] Step 3: If C1 / A1 is greater than 5, the signal-to-noise ratio is high enough and no processing is required; otherwise, proceed to step 4 to perform weak signal processing on the received signal.

[0032] Step 4: Place the receiving antenna at a certain depth point in the hole, and disable the transmitting antenna. Use the receiving antenna to collect the noise amplitude a1 and phase b1 at that depth point. Then, move the transmitting antenna in another hole according to the depth range measured by the receiving antenna. The receiving antenna collects the amplitude c1j and phase d1j of the received signal, where j = 1, 2, ..., M.

[0033] Step 5: Place the receiving antenna at another depth point in the hole, repeat step 4, and use the receiving antenna to collect the noise amplitude ai and phase bi at that depth point. Then, move the transmitting antenna in another hole according to the depth range measured by the receiving antenna, and collect the amplitude cij and phase dij of the received signal, where i = 1, 2, ..., N.

[0034] Step 6: Convert the amplitude and phase of the received signal and noise into real and imaginary parts, and subtract them at the same depth point to obtain the real and imaginary parts of the received signal after noise removal. Then convert them into amplitude and phase for subsequent imaging.

[0035] Example 1: This example discloses a method for processing weak signals in electromagnetic wave CT, including the following steps:

[0036] (1) The transmitting antenna is not working, and the receiving antenna collects noise data curves, such as Figure 4 and Figure 5 As shown.

[0037] (2) The transmitting antenna is working, and the receiving antenna measures the received signal curve, such as... Figure 6 and Figure 7 As shown.

[0038] (3) Figure 6 and Figure 4 The amplitude ratios are calculated and are all greater than 5, so no processing is required.

[0039] Figure 8 and Figure 9 For another set of noise amplitude and received signal amplitude, it can be seen that most of the ratios are less than 5, so processing is required.

[0040] (4) Process according to steps 4, 5, and 6 above. The result after processing is as follows: Figure 10 As shown, the curve shape has been significantly improved.

Claims

1. A method for processing weak signals of electromagnetic wave CT, characterized in that, The method comprises the following steps: Step 1, according to the job requirements, select the depth range and distance interval that the receiving antenna needs to measure, and use the receiving antenna to make noise measurement along the interval depth points in the hole, to obtain the noise curve varying with depth, divide the collected noise into amplitude and phase, and obtain two sets of noise curves A1 and B1 varying with depth; Step 2, place the transmitting antenna at the deepest position in another hole, turn on the power supply, transmit electromagnetic wave signals, and use the receiving antenna to make signal reception along the interval depth points in step 1, divide the received signals into amplitude and phase, and obtain two sets of received signal curves C1 and D1 varying with depth; Step 3, if C1 / A1 is greater than 5, the signal-to-noise ratio is large enough, and no processing is needed; otherwise, continue to step 4; Step 4, place the receiving antenna at a depth point in the hole, and the transmitting antenna does not work, use the receiving antenna to collect the noise amplitude a1 and phase b1 at the depth point; Then move the transmitting antenna according to the depth range measured by the receiving antenna in the other hole, and use the receiving antenna to collect the amplitude c1j and phase d1j of the received signal, where j=1, 2, …, M; Step 5, place the receiving antenna at another depth point in the hole, repeat step 4, use the receiving antenna to collect the noise amplitude ai and phase bi at the depth point, then move the transmitting antenna according to the depth range measured by the receiving antenna in the other hole, and use the receiving antenna to collect the amplitude cij and phase dij of the received signal, where i=1, 2, …, N; Step 6, convert the amplitude and phase of the received signal and noise into real part and imaginary part, subtract them at the same depth point, obtain the real part and imaginary part of the received signal after removing the noise, and then convert them into amplitude and phase, which are used for subsequent imaging.

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