Artificial source electromagnetic exploration signal processing method and system for urban power frequency interference

Abstract

The present application relates to the technical field of geophysical electromagnetic exploration, and discloses a personnel source electromagnetic exploration signal processing method and system for city power frequency interference. The method comprises: obtaining a to-be-processed signal comprising an exploration signal and a power frequency signal; performing Fourier transform, obtaining a spectrum containing only noise based on the conjugate symmetry characteristic of the spectrum leakage about the power frequency signal frequency, performing inverse Fourier transform, and then performing envelope processing; performing normalization processing on the power frequency signal part in the to-be-processed signal based on the envelope line, and then performing Fourier transform; processing the normalized spectrum to remove the power frequency signal, and performing inverse Fourier transform to obtain a processed time domain signal; multiplying the time domain signal by the envelope line, and then performing Fourier transform to correct the frequency coefficients to obtain an effective exploration signal spectrum. The present application extracts accurate and effective frequency corresponding to accurate coefficients by using the conjugate symmetry characteristic of the spectrum leakage, and eliminates the power frequency interference.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of geophysical electromagnetic exploration, in particular to a personnel source electromagnetic exploration signal processing method and system for urban power frequency interference. BACKGROUND

[0002] The statements in this section merely provide background information related to the present application and do not necessarily constitute the prior art.

[0003] Power frequency interference is a kind of interference caused by power system, which widely exists in the vicinity of power transmission, power transformation and power utilization facilities, along the electrified railway, around and in the vicinity of large buildings, etc. The domestic frequency is generally 50Hz. In urban environment, a large number of power lines, dense buildings and other facilities will produce high-intensity power frequency noise, especially in the city, the distance between the noise source and the detection equipment is closer, and the noise intensity is higher. The exploration frequency of the frequency domain electromagnetic exploration method is located in the frequency band on both sides of the power frequency, and the energy leakage caused by the power frequency interference will affect these frequency bands, thereby causing the amplitude of the effective exploration frequency (such as 48Hz, 45Hz, etc.) to be unable to be accurately obtained.

[0004] For industrial power with relatively stable frequency (50Hz), energy leakage is mainly caused by the continuous change of power consumption around the detection equipment. In the city, such change is more obvious, which is manifested as the time domain amplitude of the collected signal being different. In this case, even if the whole cycle is truncated for Fourier transform, the obtained signal spectrum will still have obvious energy leakage, and it is difficult to eliminate the interference caused by power frequency energy leakage in the effective exploration frequency (48Hz, etc.) by using the traditional band-pass filtering method. SUMMARY

[0005] In order to overcome the shortcomings of the prior art, the present application provides a personnel source electromagnetic exploration signal processing method and system for urban power frequency interference. The present application uses the conjugate symmetry characteristics of spectral leakage, combines with analytical envelope, extracts accurate and effective frequency corresponding accurate coefficient, and eliminates power frequency interference.

[0006] To achieve the above object, one or more embodiments of the present application provide the following technical solutions:

[0007] A personnel source electromagnetic exploration signal processing method for urban power frequency interference, comprising the following steps:

[0008] Obtaining a signal to be processed, the signal to be processed including an exploration signal and a power frequency signal;

[0009] Performing Fourier transform on the signal to be processed to obtain the frequency spectrum of the signal to be processed;

[0010] Based on the characteristic that the spectrum leakage is conjugate symmetric about the frequency of the power signal, a spectrum containing only noise is obtained;

[0011] The Fourier inverse transform is performed on the spectrum containing only noise, and envelope processing is performed to obtain an envelope line;

[0012] Based on the envelope line, the power signal part in the signal to be processed is normalized and then Fourier transformed to obtain a normalized spectrum;

[0013] Based on the characteristic that the spectrum leakage is conjugate symmetric about the frequency of the exploration signal, the normalized spectrum is processed to remove the power signal, and the Fourier inverse transform is performed to obtain a processed time domain signal;

[0014] The time domain signal is multiplied by the envelope line, and then Fourier transformed to obtain a new spectrum, and the frequency coefficients are corrected to obtain an effective exploration signal spectrum.

[0015] Further, obtaining a spectrum containing only noise specifically includes:

[0016] Based on the characteristic that the spectrum leakage is conjugate symmetric about the frequency of the power signal, a frequency conjugate symmetric about the frequency of the exploration signal is extracted, and the spectrum of the frequency is used to process the spectrum of the exploration signal frequency to obtain a spectrum containing only noise.

[0017] Further, the power signal is a 50Hz signal, and the exploration signal is a 48Hz signal. The spectrum frequency coefficient a+bi of 52Hz is conjugate symmetric, transformed into a-bi, and assigned to the spectrum of 48Hz to obtain a spectrum containing only noise.

[0018] Further, the envelope processing adopts Hilbert transform.

[0019] Further, processing the normalized spectrum to remove the power signal specifically includes:

[0020] Based on the characteristic that the spectrum leakage is conjugate symmetric about the frequency of the exploration signal, a frequency conjugate symmetric about the frequency of the power signal is extracted, and the spectrum of the frequency is used to process the power signal part in the normalized spectrum.

[0021] Further, the power signal is a 50Hz signal, and the exploration signal is a 48Hz signal. The spectrum frequency coefficient c+di of 46Hz is conjugate symmetric, transformed into c-di, and assigned to the spectrum of 50Hz.

[0022] Further, correcting the frequency coefficients specifically includes:

[0023] The power frequency signal is a 50Hz signal, and the exploration signal is a 48Hz signal; assuming that the frequency coefficient of the 48Hz spectrum in the obtained new spectrum is a+bi, and the frequency coefficient of the 52Hz spectrum is c+di;

[0024] For the 48Hz spectrum and the 52Hz spectrum, the frequency coefficient average of the two adjacent frequency points is used to estimate the background noise, and the frequency coefficient of the background noise is a1+b1i, c1+d1i;

[0025] Assuming that the envelope error frequency coefficient in the 52Hz spectrum is c-c1+(d-d1)i, based on the characteristic of the conjugate symmetry of the envelope error, the envelope error of the 48Hz spectrum is estimated, and the frequency coefficient is c-c1-(d-d1)i;

[0026] Then the effective part frequency coefficient in the 48Hz spectrum is a-a1-(c-c1)+[b-b1+(d-d1)]i, and the new spectrum is corrected.

[0027] One or more embodiments provide an artificial source electromagnetic exploration signal processing system for urban power frequency interference, comprising:

[0028] An original signal acquisition module is configured to acquire a to-be-processed signal, wherein the to-be-processed signal comprises an exploration signal and a power frequency signal;

[0029] A time-space domain conversion module is configured to perform Fourier transform on the to-be-processed signal to obtain a frequency spectrum of the to-be-processed signal;

[0030] A leakage spectrum obtaining module is configured to obtain a spectrum containing only noise based on the characteristic that the spectrum leakage is conjugate symmetric about the power frequency signal frequency;

[0031] An envelope line calculation module is configured to perform inverse Fourier transform on the spectrum containing only noise, and then perform envelope processing to obtain an envelope line;

[0032] An original signal normalization module is configured to perform normalization processing on the power frequency signal part in the to-be-processed signal based on the envelope line, and then perform Fourier transform to obtain a normalized frequency spectrum;

[0033] A power frequency signal removal module is configured to perform processing on the normalized frequency spectrum based on the characteristic that the spectrum leakage is conjugate symmetric about the exploration signal frequency, to remove the power frequency signal, and then perform inverse Fourier transform to obtain a processed time domain signal;

[0034] An effective signal determination module is configured to multiply the time domain signal by the envelope line, and then perform Fourier transform to obtain a new frequency spectrum, and correct the frequency coefficient to obtain an effective exploration signal spectrum.

[0035] One or more embodiments provide an electronic device, comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, wherein the processor implements the method for processing artificial source electromagnetic exploration signal of urban power frequency interference when executing the program.

[0036] One or more embodiments provide a computer readable storage medium, having stored thereon a computer program, wherein the program is executed by a processor to implement the method for processing artificial source electromagnetic exploration signal of urban power frequency interference.

[0037] The above one or more technical solutions have the following beneficial effects:

[0038] A method for processing artificial source electromagnetic exploration signal of urban power frequency interference is provided, which fully utilizes the characteristic of the conjugate symmetry of the frequency spectrum leakage with respect to the power frequency signal frequency, extracts a signal containing only noise from the collected mixed signal, calculates the envelope line of the noise part signal, accurately reflects the change of the power frequency, and performs normalization processing on the collected original signal based on the envelope line, so that the power frequency part in the original signal becomes an approximate periodic signal, and the energy leakage is effectively suppressed.

[0039] In addition, the consistency of the error of the frequency band on both sides of the power frequency is utilized to reduce the calculation error of the artificial source transmitting frequency, obtain a more accurate frequency coefficient, and effectively reduce the influence of urban power frequency interference. BRIEF DESCRIPTION OF DRAWINGS

[0040] The accompanying drawings, which form a part of this description, are included to provide a further understanding of the application and are incorporated in and constitute a part of this application. The embodiments of the application illustrated in the drawings are intended to explain the aspects of the present application and are not intended to limit the present application in any manner.

[0041] Figure 1 is a time domain waveform (a) and a spectrum graph (b) of power frequency energy leakage.

[0042] Figure 2 is a Hilbert analytical envelope graph of the noise part;

[0043] Figure 3 is a normalized time domain waveform graph (a) and a spectrum graph (b) of the original signal to be processed;

[0044] Figure 4 is a comparison graph of the time domain waveform of the power frequency interference before (a) and after (b) denoising;

[0045] Figure 5 is a comparison graph of the spectrum before and after denoising of the power frequency interference (50Hz and its surrounding frequency band). DETAILED DESCRIPTION

[0046] The application will be further described below with reference to the drawings and embodiments.

[0047] It should be noted that the following detailed description is exemplary in nature and is intended to provide further description of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0048] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments in accordance with the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, steps, operations, elements, components, and / or groups thereof, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or groups thereof.

[0049] The embodiments in the application and the features in the embodiments can be combined with each other without conflict.

[0050] Embodiment one

[0051] The embodiment discloses a method for processing artificial source electromagnetic exploration signals for urban power frequency interference, comprising the following steps:

[0052] Step 1: obtaining a signal to be processed, the signal to be processed comprising an exploration signal and a power frequency signal.

[0053] Specifically, the power frequency signal is a 50Hz signal, and the exploration signal is a 48Hz signal.

[0054] Step 2: Fourier transforming the signal to be processed to transform from the time domain to the frequency domain, and obtaining the frequency spectrum of the signal to be processed.

[0055] Due to the existence of spectral leakage, after Fourier transforming the signal to be processed, it can be seen that the signal to be processed contains signals of other frequencies, such as 46Hz and 52Hz, in addition to the 50Hz signal and the 48Hz signal.

[0056] Step 3: based on the characteristic that the power frequency signal frequency is conjugate symmetric, extracting a frequency conjugate symmetric to the exploration signal frequency, processing the spectrum of the exploration signal frequency based on the spectrum of the frequency, and obtaining a spectrum containing only noise.

[0057] By analyzing the spectrum of the signal to be processed, it can be found that the spectrum of the 48Hz signal contains both effective signals and spectrum leakage signals. In order to suppress the spectrum leakage signals, the embodiment is based on the characteristic that the spectrum leakage of 50Hz has symmetrical characteristics (conjugate symmetry) on both sides, extracts the 52Hz spectrum which is conjugate symmetric to the 48Hz spectrum with respect to 50Hz, and processes the 48Hz spectrum based on the 52Hz spectrum to obtain a spectrum containing only noise.

[0058] Specifically, the frequency coefficient (a+bi) of 52Hz is conjugate symmetrically transformed and then assigned to 48Hz (a-bi) to obtain a signal containing only spectrum. Those skilled in the art can understand that 48Hz and 52Hz are not strictly symmetrical, and the spectrum containing only noise obtained here is an estimate, in which there is still a small 48Hz periodic signal.

[0059] Step 4: Fourier inverse transform is performed on the spectrum containing only noise to convert from the frequency domain to the time domain, and then envelope processing is performed to obtain an envelope curve.

[0060] The time domain reconstruction signal waveform of the spectrum containing only noise is shown in Figure 2 The embodiment adopts Hilbert transform for envelope processing to obtain an envelope curve of two norms, and the envelope curve is an amplitude transformation curve of the power frequency. Due to the existence of the 48Hz periodic signal in the spectrum containing only noise, the envelope curve has errors.

[0061] Specifically, the Hilbert transform delays the signal phase by 90°, and the Hilbert envelope curve of the noise part is shown in Figure 3 The envelope curve reflects the amplitude variation of 50Hz.

[0062] Step 5: Based on the modulus of the envelope curve, the power frequency signal part in the signal to be processed is normalized, and then Fourier transform is performed to obtain a normalized spectrum.

[0063] The original collected signal is divided by the modulus of the envelope curve (i.e. the amplitude transformation curve of the power frequency), which realizes the normalization processing of the power frequency, and the result is shown in Figure 3 a. The signal shown in Figure 3 a is subjected to Fourier transform, and the result is shown in Figure 3 b, and the energy aggregation after normalization no longer leaks. The normalized spectrum will have three pulses of 48Hz, 50Hz and 52Hz.

[0064] Since the 48Hz exploration signal in the original signal to be processed is a periodic signal, it becomes a non-periodic signal after being divided by the envelope curve, which also produces leakage, and this leakage still has conjugate symmetry characteristics. Based on this, the following processing is also performed.

[0065] Step 6: Based on the characteristic of the conjugate symmetry of the spectrum leakage with respect to the frequency of the exploration signal, a frequency conjugate symmetric with the frequency of the power frequency signal is extracted, the power frequency signal part in the normalized spectrum is processed based on the spectrum of the frequency, and then inverse Fourier transform is performed to obtain a processed time domain signal.

[0066] In order to further suppress the spectrum leakage signal, the embodiment is based on the characteristic that the spectrum leakage of 48Hz has symmetric characteristics (conjugate symmetry) on both sides, and extracts the 46Hz spectrum conjugate symmetric with respect to the 48Hz spectrum of the 50Hz spectrum. Since the 46Hz spectrum is all leakage spectrum, the 50Hz spectrum is processed based on the 46Hz spectrum to ensure the accuracy of the 48Hz effective signal. Specifically, the spectrum frequency coefficient (c+di) of 46Hz is conjugate symmetric, which is transformed into (c-di) and assigned to the spectrum of 50Hz.

[0067] Step 7: Multiply the time domain signal by the modulus of the envelope line, and then perform Fourier transform to obtain a new spectrum, and correct the frequency coefficient to obtain an effective exploration signal.

[0068] After the above processing, the power frequency energy is reduced, and the leakage is reduced. The spectrum of 48Hz contains effective signals, envelope errors and background noise; the spectrum of 52Hz contains envelope errors and background noise.

[0069] Suppose the frequency coefficient of 48Hz is a+bi, and the frequency coefficient of 52Hz is c+di. The average of the frequency coefficients of the adjacent two frequency points is used to estimate their background noise as a1+b1i,c1+d1i.

[0070] Based on the characteristic of the conjugate symmetry of the envelope error, the envelope error in 52Hz is c-c1+(d-d1)i, and the envelope error in 48Hz is c-c1-(d-d1)i.

[0071] The effective signal frequency coefficient in 48Hz is a-a1-(c-c1)+[b-b1+(d-d1)]i.

[0072] Based on the obtained effective signal frequency coefficient, the new spectrum is corrected to obtain an effective exploration signal spectrum.

[0073] Embodiment two

[0074] Based on the method provided in the above embodiment one, the embodiment provides a man-made source electromagnetic exploration signal processing system for urban power frequency interference, which comprises:

[0075] An original signal acquisition module is configured to acquire a to-be-processed signal, wherein the to-be-processed signal comprises an exploration signal and a power frequency signal.

[0076] a time-domain space-domain conversion module, configured to perform Fourier transform on the to-be-processed signal to obtain a frequency spectrum of the to-be-processed signal;

[0077] a leakage spectrum obtaining module, configured to obtain a spectrum containing only noise based on the characteristic that the frequency spectrum leakage is conjugate symmetric about the frequency of the power frequency signal;

[0078] an envelope line calculating module, configured to perform inverse Fourier transform on the spectrum containing only noise, and then perform envelope processing to obtain an envelope line;

[0079] an original signal normalizing module, configured to perform normalization processing on the power frequency signal part in the to-be-processed signal based on the envelope line, and then perform Fourier transform to obtain a normalized frequency spectrum;

[0080] a power frequency signal removing module, configured to perform processing on the normalized frequency spectrum based on the characteristic that the frequency spectrum leakage is conjugate symmetric about the frequency of the exploration signal, to remove the power frequency signal, and then perform inverse Fourier transform to obtain a processed time-domain signal;

[0081] an effective signal determining module, configured to multiply the time-domain signal by the envelope line, and then perform Fourier transform to obtain a new frequency spectrum, and correct frequency coefficients to obtain an effective exploration signal frequency spectrum.

[0082] Embodiment Three

[0083] An object of the embodiment is to provide an electronic device.

[0084] An electronic device includes a memory, a processor, and a computer program stored in the memory and executable on the processor, and the processor implements the method for processing an artificial source electromagnetic exploration signal of a city power frequency interference as described in Embodiment One when executing the program.

[0085] Embodiment Four

[0086] An object of the embodiment is to provide a computer-readable storage medium.

[0087] A computer-readable storage medium has a computer program stored thereon, and the program, when executed by a processor, implements the method for processing an artificial source electromagnetic exploration signal of a city power frequency interference as described in Embodiment One.

[0088] The steps and methods involved in Embodiments Two, Three, and Four correspond to Embodiment One, and the specific embodiments can be referred to the relevant description part of Embodiment One.

[0089] The above describes the specific embodiments of the present application in combination with the drawings, but is not a limitation on the protection scope of the present application. Those skilled in the art should understand that various modifications or variations made by those skilled in the art on the basis of the technical solutions of the present application without creative labor are still within the protection scope of the present application.

Claims

1. A method for processing artificial source electromagnetic exploration signals against urban power frequency interference, characterized in that, The method comprises the following steps: obtaining a signal to be processed, wherein the signal to be processed comprises an exploration signal and a power frequency signal; performing Fourier transform on the signal to be processed to obtain a frequency spectrum of the signal to be processed; obtaining a frequency spectrum containing only noise based on the characteristic that the spectrum leakage is conjugate symmetric with respect to the frequency of the power frequency signal; performing Fourier inverse transform on the frequency spectrum containing only noise and then performing envelope processing to obtain an envelope line; performing normalization processing on the power frequency signal part in the signal to be processed based on the envelope line, and then performing Fourier transform to obtain a normalized frequency spectrum; processing the normalized frequency spectrum based on the characteristic that the spectrum leakage is conjugate symmetric with respect to the frequency of the exploration signal, removing the power frequency signal, and performing Fourier inverse transform to obtain a processed time domain signal; multiplying the time domain signal by the envelope line, and then performing Fourier transform to obtain a new frequency spectrum, and correcting the frequency coefficients to obtain an effective exploration signal spectrum.

2. The method for artificial source electromagnetic exploration signal processing against urban power frequency interference according to claim 1, characterized in that, The step of obtaining a frequency spectrum containing only noise specifically comprises: extracting a frequency conjugate symmetric with respect to the frequency of the exploration signal based on the characteristic that the spectrum leakage is conjugate symmetric with respect to the frequency of the power frequency signal, and processing the frequency spectrum of the exploration signal based on the frequency spectrum of the extracted frequency to obtain the frequency spectrum containing only noise.

3. The method for artificial source electromagnetic exploration signal processing against urban power frequency interference according to claim 2, characterized in that, The power frequency signal is a 50 Hz signal, and the exploration signal is a 48 Hz signal; the frequency spectrum frequency coefficient a+bi of 52 Hz is conjugate symmetric, is transformed into a-bi, and is assigned to the frequency spectrum of 48 Hz to obtain the frequency spectrum containing only noise.

4. The method for artificial source electromagnetic exploration signal processing against urban power frequency interference according to claim 1, characterized in that, The envelope processing adopts Hilbert transform.

5. The method for artificial source electromagnetic exploration signal processing against urban power frequency interference according to claim 1, characterized in that, The step of processing the normalized frequency spectrum to remove the power frequency signal specifically comprises: extracting a frequency conjugate symmetric with respect to the frequency of the power frequency signal based on the characteristic that the spectrum leakage is conjugate symmetric with respect to the frequency of the exploration signal, and processing the power frequency signal part in the normalized frequency spectrum based on the frequency spectrum of the extracted frequency.

6. The method for artificial source electromagnetic exploration signal processing against urban power frequency interference according to claim 5, characterized in that, The power frequency signal is a 50 Hz signal, and the exploration signal is a 48 Hz signal; the frequency spectrum frequency coefficient c+di of 46 Hz is conjugate symmetric, is transformed into c-di, and is assigned to the frequency spectrum of 50 Hz.

7. The method for artificial source electromagnetic exploration signal processing against urban power frequency interference according to claim 1, characterized in that, The step of correcting the frequency coefficients specifically comprises: the power frequency signal is a 50 Hz signal, and the exploration signal is a 48 Hz signal; the frequency coefficient of the 48 Hz frequency spectrum in the obtained new frequency spectrum is a+bi, and the frequency coefficient of the 52 Hz frequency spectrum is c+di; for the 48 Hz frequency spectrum and the 52 Hz frequency spectrum, the frequency coefficients of two adjacent frequency points are averaged to obtain background noise, and the frequency coefficients of the background noise are a1+b1i and c1+d1i; the envelope error frequency coefficient in the 52 Hz frequency spectrum is c-c1+(d-d1)i, and based on the characteristic that the envelope error is conjugate symmetric, the envelope error of the 48 Hz frequency spectrum is obtained, and the frequency coefficient is c-c1-(d-d1)i; then, the effective part frequency coefficient in the 48 Hz frequency spectrum is a-a1-(c-c1)+[b-b1+(d-d1)]i, and the new frequency spectrum is corrected.

8. A system for processing artificial source electromagnetic prospecting signals against urban power frequency interference, characterized in that it comprises: It comprises: an original signal acquisition module, configured to obtain a signal to be processed, wherein the signal to be processed comprises an exploration signal and a power frequency signal; A time-space conversion module is configured to perform Fourier transform on the to-be-processed signal to obtain a frequency spectrum of the to-be-processed signal; A leakage spectrum obtaining module is configured to obtain a spectrum containing only noise based on the characteristic that the frequency spectrum leakage is conjugate symmetric about the frequency of the power signal; An envelope line calculating module is configured to perform inverse Fourier transform on the spectrum containing only noise and then perform envelope processing to obtain an envelope line; An original signal normalizing module is configured to perform normalization processing on the power signal part in the to-be-processed signal based on the envelope line, and then perform Fourier transform to obtain a normalized frequency spectrum; A power signal removing module is configured to perform processing on the normalized frequency spectrum based on the characteristic that the frequency spectrum leakage is conjugate symmetric about the frequency of the exploration signal, remove the power signal, and perform inverse Fourier transform to obtain a processed time-domain signal; An effective signal determining module is configured to multiply the time-domain signal by the envelope line, perform Fourier transform to obtain a new frequency spectrum, and correct frequency coefficients to obtain an effective exploration signal spectrum.

9. An electronic device comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, characterized in that, The processor executes the program to implement the artificial source electromagnetic exploration signal processing method for urban power frequency interference according to any one of claims 1-7.

10. A computer-readable storage medium having stored thereon a computer program, characterized in that, The program is executed by the processor to implement the artificial source electromagnetic exploration signal processing method for urban power frequency interference according to any one of claims 1-7.

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