Artificial source electromagnetic near-field detection method and system based on high-order pseudo-random signal

Abstract

The present invention relates to the field of geophysical electromagnetic exploration technology, and provides a near-field detection method and system for artificial source electromagnetic methods based on high-order pseudo-random signals. Based on the periodic characteristics of Fourier transform, the acquired transmitted and received signals are initially phase-aligned to ensure that the time difference between the recording moments is an integer multiple of the minimum period of the signal itself. Fast Fourier transforms are performed on the processed transmitted and received signals to extract the dominant frequency components. Frequency domain correlation identification processing is performed on the dominant frequency components of the two signals, and deconvolution is performed to obtain a series of discrete amplitude and phase information. The discrete amplitude and phase information is interpolated to obtain amplitude and phase information within the full frequency band. Based on the complex conjugation of the spectrum, the time domain earth impulse response is recovered through inverse Fourier transform. The present invention achieves the recovery of the time domain impulse response based on the discrete dominant frequency, thereby improving accuracy.

Description

Technical Field

[0001] The present invention belongs to the technical field of geophysical electromagnetic exploration, and in particular relates to a near-field detection method and system using an artificial source electromagnetic method based on high-order pseudo-random signals. Background Art

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

[0003] Electromagnetic exploration is a type of geophysical exploration method that uses the electrical properties of underground media to study underground structures by observing the distribution of natural or artificial electromagnetic fields, with the goal of solving engineering and environmental problems. Artificial source electromagnetic methods can be divided into frequency domain and time domain methods based on the type of transmitted signal. However, current frequency domain and time domain electromagnetic methods still have limited adaptability for near-field exploration.

[0004] Most frequency-domain artificial source electromagnetic methods follow the plane wave approximation of magnetotellurics and employ corresponding formulas for calculating wave impedance and apparent resistivity. However, this assumption applies only in the far range, meaning the distance from the measurement point to the field source must be significantly greater than the skin depth. In the near range, electromagnetic field propagation differs from that in the far range, resulting in a 45° upward trend in apparent resistivity. Therefore, traditional frequency-domain artificial source electromagnetic methods are poorly suited for near-field exploration. Due to the separability of the primary and secondary fields in the time domain, time-domain electromagnetic methods can achieve greater detection depths with shorter transmission and reception distances. However, due to the requirement for continuous measurement, time-domain electromagnetic methods are relatively weak in anti-interference capabilities, particularly for late signals from deep formations. Summary of the Invention

[0005] To solve the above problems, the present invention proposes a near-field detection method and system for artificial source electromagnetic method based on high-order pseudo-random signals. Based on the uniform and wide-spectrum characteristics of high-order pseudo-random signals, the present invention utilizes the amplitude and phase information of a limited number of main frequencies to achieve the acquisition of frequency-discrete coefficients to time-continuous earth impulse responses, providing a new method for near-field processing and interpretation of artificial source frequency domain electromagnetic method.

[0006] According to some embodiments, the present invention adopts the following technical solutions:

[0007] A near-field detection method using an artificial source electromagnetic method based on a high-order pseudo-random signal comprises the following steps:

[0008] Simultaneously obtain the prefabricated wideband high-order pseudo-random signal transmitted by the transmitter and the received signal by the receiver;

[0009] Based on the periodic characteristics of Fourier transform, the acquired transmitted and received signals are initially phase-aligned to ensure that the time difference between the two recording moments is an integer multiple of the minimum period of the signal itself;

[0010] Perform fast Fourier transform on the processed transmit and receive signals respectively to extract the main frequency components;

[0011] The main frequency components of the two are subjected to frequency domain correlation identification processing, and deconvolution is used to obtain a series of discrete amplitude and phase information;

[0012] The discrete amplitude and phase information is interpolated to obtain the amplitude and phase information within the full frequency band, and based on the complex conjugation of the spectrum, the time domain earth impulse response is restored through inverse Fourier transform.

[0013] As an optional implementation, the preset broadband high-order pseudo-random signal is of type L6-F81, which includes 6 frequency groups and a total of 81 main frequency components. The main frequency components are the frequencies where the energy of the high-order pseudo-random signal is concentrated; the main frequency components range from 0.125 Hz to 6144 Hz, and the minimum period is 8s. The construction equation is written as:

[0014] ;

[0015] in, It is the basic construction unit of a series of step signals. When constructing non-logarithmic uniform signals, it is necessary to select The highest frequency and the lowest frequency in the , that is, the custom basic unit for building high-order pseudo-random signals, the sign function is the symbol function, is a set of high-order pseudo-random signals.

[0016] As an optional implementation, the transmitting end is a grounded long wire source within a set length range, and the set length range is [1 km, 2 km].

[0017] As an optional implementation manner, the receiving end is constructed by electrodes parallel to the transmitting end within a transmitting and receiving distance range, and the transmitting and receiving distance range is [3 km, 6 km].

[0018] As an optional implementation, the periodic characteristic of the Fourier transform is that the phase information of the signal does not change when the minimum period is increased by an integer multiple.

[0019] As an optional implementation method, the process of performing frequency domain correlation identification processing on the main frequency components of the two includes: conjugate with it Multiply to get the transmit power spectrum ; and the main frequency component of the received signal The conjugate of its corresponding transmitted signal Multiply to get the cross power spectral density ; Then the cross power spectral density and the transmit power spectrum Dividing the two, we get the transfer function , which is the discrete impulse response spectrum.

[0020] As an optional implementation, the process of interpolating the discrete amplitude and phase information includes using a cubic Hermite interpolation method to interpolate the amplitude and phase separately with minimum frequency resolution.

[0021] A near-field detection method using an artificial source electromagnetic method based on a high-order pseudo-random signal comprises the following steps:

[0022] a signal acquisition module configured to simultaneously acquire a prefabricated wideband high-order pseudo-random signal transmitted by the transmitting end and a received signal by the receiving end;

[0023] The initial alignment module is configured to perform initial phase alignment on the acquired transmit and receive signals based on the periodic characteristics of Fourier transform, ensuring that the time difference between the two recording moments is an integer multiple of the minimum period of the signal itself;

[0024] The main frequency component extraction module is configured to perform fast Fourier transform on the processed transmission signal and the received signal respectively to extract the main frequency component therein;

[0025] The deconvolution module is configured to perform frequency domain correlation identification processing on the main frequency components of the two, and deconvolution obtains a series of discrete amplitude and phase information;

[0026] The signal recovery module is configured to interpolate the discrete amplitude and phase information to obtain the amplitude and phase information within the full frequency band, and based on the complex conjugation of the spectrum, restore the time domain earth impulse response through inverse Fourier transform.

[0027] A computer-readable storage medium is used to store computer instructions, and when the computer instructions are executed by a processor, the steps in the above method are completed.

[0028] An electronic device includes a memory and a processor, and computer instructions stored in the memory and executed on the processor. When the computer instructions are executed by the processor, the steps in the above method are completed.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The present invention establishes a relationship between the emission current and the earth pulse response, thereby realizing an innovative technical path of recovering the time domain pulse response based on the discrete main frequency.

[0031] The present invention provides a frequency domain deconvolution process based on the main frequency of a high-order pseudo-random signal to obtain a series of discrete amplitude and phase information, and realizes the recovery of the full-band amplitude and phase of the impulse response through the cubic Hermite interpolation (PCHIP) method.

[0032] Conventional frequency-domain artificial source electromagnetic methods, based on the plane wave approximation, result in a 45° upward trend in the apparent resistivity of the near-field. This paper, by combining discrete frequency deconvolution with a quasi-Fourier transform to recover the time-domain impulse response, provides a new and effective method for processing and interpreting frequency-domain electromagnetic data in near-field exploration.

[0033] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, preferred embodiments are given below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0035] Figure 1 A diagram of a field observation device for extracting a time-domain earth impulse response based on a high-order pseudo-random signal according to an embodiment;

[0036] Figure 2 Schematic diagram of the time series and spectrum of the transmitted and received signals of an embodiment, wherein (a) is a waveform diagram of the transmitted signal, (b) is a waveform diagram of the received signal, (c) is a spectrum diagram of the transmitted signal, and (d) is a spectrum diagram of the received signal;

[0037] Figure 3 Schematic diagram of the amplitude and phase results and interpolation curves of deconvolution according to an embodiment, wherein (a) is a schematic diagram of the amplitude identification result and the interpolation curve, and (b) is a schematic diagram of the phase identification result and the interpolation curve;

[0038] Figure 4 3 is a comparison diagram of the deconvolution result of the earth electric field pulse response and the analytical solution of an embodiment. DETAILED DESCRIPTION

[0039] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0040] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0041] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0042] In the absence of conflict, the embodiments and features in the embodiments of this application can be combined with each other.

[0043] Example 1

[0044] A near-field detection method using an artificial source electromagnetic method based on a high-order pseudo-random signal comprises the following steps:

[0045] Simultaneously obtain the prefabricated wideband high-order pseudo-random signal transmitted by the transmitter and the received signal by the receiver;

[0046] Based on the periodic characteristics of Fourier transform, the acquired transmitted and received signals are initially phase-aligned to ensure that the time difference between the two recording moments is an integer multiple of the minimum period of the signal itself;

[0047] Perform fast Fourier transform on the processed transmit and receive signals respectively to extract the main frequency components;

[0048] The main frequency components of the two are subjected to frequency domain correlation identification processing, and deconvolution is used to obtain a series of discrete amplitude and phase information;

[0049] The discrete amplitude and phase information is interpolated to obtain the amplitude and phase information within the full frequency band, and based on the complex conjugation of the spectrum, the time domain earth impulse response is restored through inverse Fourier transform.

[0050] In this embodiment, an electrical long conductive source is arranged to transmit a customized broadband high-order pseudo-random signal, the signal is recorded at the transmitting end and the receiving end, and the signal is preprocessed to achieve initial phase alignment of the transmitted and received signals.

[0051] like Figure 1 As shown, in this embodiment, the transmitting end is a long wire source of 1 km to 2 km, and the signal modulation unit controls the transmission of the high-order pseudo-random signal. Within the transmission and reception range of 3 km to 6 km, the electric field component is received by electrodes arranged parallel to the long wire.

[0052] The default broadband high-order pseudo-random signal is L6-F81 type, such as Figure 2 (a) and Figure 2As shown in (b), it contains 6 frequency groups and a total of 81 main frequency components. The main frequency components range from 0.125 Hz to 6144 Hz, and the minimum period is 8s.

[0053] The construction equation is written as:

[0054] ;

[0055] in, It is the basic construction unit of a series of step signals. When constructing non-logarithmic uniform signals, it is necessary to select The highest frequency and the lowest frequency in the , that is, the custom basic unit for constructing high-order (non-logarithmic uniform) pseudo-random signals, the sign function is the symbol function, is a set of high-order pseudo-random signals.

[0056] In this embodiment, the transmitting end is powered by a high-power diesel generator, which provides stable power for the broadband signal transmitter. The transmitting signal is modulated by the signal control unit and measured by the grounded receiver.

[0057] The preprocessing process of this embodiment performs initial phase alignment on the acquired transmission signal and reception signal based on the periodic characteristics of Fourier transform.

[0058] When the two are not collected at the same time, it is only necessary to truncate the data with a length not exceeding one minimum cycle so that the recording start time difference is an integer multiple of the minimum cycle of the signal to achieve effective phase alignment.

[0059] Among them, the periodic characteristic of Fourier transform is that the phase information of the signal will not change when the minimum period increases by an integer multiple.

[0060] Figure 2 (b) and Figure 2 Figure (c) shows the time series and spectrum of the received signal, respectively. After preprocessing, the initial phases of the transmitted and received signals are perfectly aligned. This example shows five periods (40 seconds) of the transmitted and received signals at the same time. Furthermore, if the transmitted and received signals are not recorded perfectly synchronously, but the time difference is an integer multiple of the minimum period (1 / 0.125H = 8 seconds), the initial phases of the two signals can still be aligned.

[0061] The dominant frequency components are frequency components with concentrated energy in the spectrum of a high-order pseudo-random signal. These frequency components have uniform energy and are relatively evenly spaced on a logarithmic scale. For example, the spectrum of an L6-F81 high-order pseudo-random signal contains 81 dominant frequency components with uniform energy and relatively evenly spaced on a logarithmic scale.

[0062] The process of frequency domain correlation identification of the main frequency components of the two includes: extracting the information of the main frequency components of the transmitted and received signals, and then deconvolving the two through correlation identification to obtain the amplitude and phase information of the discrete impulse response, and restoring the amplitude and phase information of the full frequency band through Hermite interpolation to obtain the main frequency components of the transmitted signal. conjugate with it Multiply to get the transmit power spectrum ; and the main frequency component of the received signal The conjugate of its corresponding transmitted signal Multiply to get the cross power spectral density ; Then the cross power spectral density and the transmit power spectrum Dividing the two, we get the transfer function , which is the discrete impulse response spectrum.

[0063] The relevant formula of the deconvolution method for correlation identification can be written as:

[0064] ;

[0065] ;

[0066] ;

[0067] ;

[0068] in, Represents the power spectral density of the emission current spectrum; Represents the cross-power spectral density, which is used to reflect the correlation between the received signal and the transmitted signal in the frequency domain; and are the spectra of the received and transmitted signals respectively; is the transfer function, which is used to describe the transfer characteristics of the signal; To recover the earth impulse response, is the signal sampling rate.

[0069] In this embodiment, the process of interpolating discrete amplitude and phase information includes using a cubic Hermite interpolation method to interpolate the amplitude and phase separately with minimum frequency resolution, thereby preserving the monotonicity of the frequency response data at both ends.

[0070] During the interpolation process, Figure 3 (a) and Figure 3As shown in (b), this example aims to recover an 8-second impulse response. The specified signal sampling rate is 16384 Hz, with a minimum frequency resolution of 0.125 Hz. Therefore, the amplitude and phase must be interpolated within the range of 0.125 Hz to 8192 Hz with a resolution of 0.125 Hz. Furthermore, based on the complex conjugation property of the Fourier transform, the negative frequency response is supplemented to construct a complete spectral representation. Finally, the inverse Fourier transform is used to recover the earth's electric field impulse response.

[0071] like Figure 4 As shown in FIG, the deconvolution result of the earth electric field impulse response is compared with the analytical solution. The red dots are the analytical solution, and the blue solid line is the earth impulse response obtained by deconvolution. It can be seen that the method provided in this embodiment has high accuracy.

[0072] Example 2

[0073] A near-field detection method using an artificial source electromagnetic method based on a high-order pseudo-random signal comprises the following steps:

[0074] a signal acquisition module configured to simultaneously acquire a prefabricated wideband high-order pseudo-random signal transmitted by the transmitting end and a received signal by the receiving end;

[0075] The initial alignment module is configured to perform initial phase alignment on the acquired transmit and receive signals based on the periodic characteristics of Fourier transform, ensuring that the time difference between the two recording moments is an integer multiple of the minimum period of the signal itself;

[0076] The main frequency component extraction module is configured to perform fast Fourier transform on the processed transmission signal and the received signal respectively to extract the main frequency component therein;

[0077] The deconvolution module is configured to perform frequency domain correlation identification processing on the main frequency components of the two, and deconvolution obtains a series of discrete amplitude and phase information;

[0078] The signal recovery module is configured to interpolate the discrete amplitude and phase information to obtain the amplitude and phase information within the full frequency band, and based on the complex conjugation of the spectrum, restore the time domain earth impulse response through inverse Fourier transform.

[0079] Example 3

[0080] A computer-readable storage medium is used to store computer instructions, which, when executed by a processor, complete the steps of the method provided in embodiment 1.

[0081] Example 4

[0082] An electronic device includes a memory and a processor, and computer instructions stored in the memory and executed on the processor. When the computer instructions are executed by the processor, the steps of the method provided in embodiment 1 are completed.

[0083] It will be understood by those skilled in the art that embodiments of the present invention may be provided as methods, systems, or computer program products. Thus, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of one or more computer-usable storage media (including but not limited to disk storage, CD - ROM , optical storage, etc.).

[0084] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowcharts and / or block diagrams, as well as combinations of processes and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowcharts and / or block diagrams. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0085] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0086] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0087] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made by those skilled in the art that fall within the spirit and principles of the present invention and do not require creative effort are intended to be within the scope of protection of the present invention.

Claims

1. A near-field detection method using an artificial source electromagnetic method based on a high-order pseudo-random signal, characterized in that: The following steps are involved: Simultaneously obtain the prefabricated wideband high-order pseudo-random signal transmitted by the transmitter and the received signal by the receiver; Based on the periodic characteristics of Fourier transform, the acquired transmitted and received signals are initially phase-aligned to ensure that the time difference between the two recording moments is an integer multiple of the minimum period of the signal itself; Perform fast Fourier transform on the processed transmit and receive signals respectively to extract the main frequency components; The main frequency components of the two are subjected to frequency domain correlation identification processing, and deconvolution is used to obtain a series of discrete amplitude and phase information; The discrete amplitude and phase information is interpolated to obtain the amplitude and phase information within the full frequency band, and based on the complex conjugation of the spectrum, the time domain earth impulse response is restored through inverse Fourier transform.

2. The near-field detection method of artificial source electromagnetic method based on high-order pseudo-random signal according to claim 1, characterized in that: The prefabricated broadband high-order pseudo-random signal is of type L6-F81, which contains 6 frequency groups and a total of 81 main frequency components. The main frequency components are the frequencies where the energy of the high-order pseudo-random signal is concentrated. The main frequency components range from 0.125 Hz to 6144 Hz, and the minimum period is 8s. The construction equation is written as: ； in, It is the basic construction unit of a series of step signals. When constructing non-logarithmic uniform signals, it is necessary to select The highest frequency and the lowest frequency in the , that is, the custom basic unit for building high-order pseudo-random signals, the sign function is the symbol function, is a set of high-order pseudo-random signals.

3. The near-field detection method of artificial source electromagnetic method based on high-order pseudo-random signal according to claim 1, characterized in that: The transmitting end is a grounded long wire source within a set length range, and the set length range is [1 km, 2 km].

4. The near-field detection method of artificial source electromagnetic method based on high-order pseudo-random signal according to claim 1, characterized in that: The receiving end is constructed by electrodes parallel to the transmitting end within the transmitting and receiving distance range, and the transmitting and receiving distance range is [3km, 6km].

5. The near-field detection method of artificial source electromagnetic method based on high-order pseudo-random signal according to claim 1, characterized in that: The periodic characteristic of the Fourier transform is that the phase information of the signal will not change when the minimum period increases by an integer multiple.

6. The near-field detection method of artificial source electromagnetic method based on high-order pseudo-random signal according to claim 1, characterized in that: The process of frequency domain correlation identification of the main frequency components of the two includes: conjugate with it Multiply to get the transmit power spectrum ; and the main frequency component of the received signal The conjugate of its corresponding transmitted signal Multiply to get the cross power spectral density ; Then the cross power spectral density and the transmit power spectrum Dividing the two, we get the transfer function , which is the discrete impulse response spectrum.

7. The near-field detection method of artificial source electromagnetic method based on high-order pseudo-random signal according to claim 1, characterized in that: The process of interpolating the discrete amplitude and phase information includes using a cubic Hermite interpolation method to interpolate the amplitude and phase separately with minimum frequency resolution.

8. A near-field detection method using artificial source electromagnetic method based on high-order pseudo-random signals, characterized in that: The following steps are involved: a signal acquisition module configured to simultaneously acquire a prefabricated wideband high-order pseudo-random signal transmitted by the transmitting end and a received signal by the receiving end; The initial alignment module is configured to perform initial phase alignment on the acquired transmit and receive signals based on the periodic characteristics of Fourier transform, ensuring that the time difference between the two recording moments is an integer multiple of the minimum period of the signal itself; The main frequency component extraction module is configured to perform fast Fourier transform on the processed transmission signal and the received signal respectively to extract the main frequency component therein; The deconvolution module is configured to perform frequency domain correlation identification processing on the main frequency components of the two, and deconvolution obtains a series of discrete amplitude and phase information; The signal recovery module is configured to interpolate the discrete amplitude and phase information to obtain the amplitude and phase information within the full frequency band, and based on the complex conjugation of the spectrum, restore the time domain earth impulse response through inverse Fourier transform.

9. A computer-readable storage medium, characterized in that: Used to store computer instructions, which, when executed by a processor, complete the steps of the method according to any one of claims 1 to 7.

10. An electronic device, characterized in that: The method comprises a memory and a processor, and computer instructions stored in the memory and executed on the processor, wherein the steps of the method according to any one of claims 1 to 7 are completed when the computer instructions are executed by the processor.

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