A method for layout and parameter design of ground-to-air frequency domain electromagnetic close-frequency dual-angle field sources

Abstract

The present invention belongs to the field of electromagnetic detection, and is a method for laying out and designing parameters of ground-to-air frequency domain electromagnetic near-frequency dual-angle field sources. Two emission sources are laid out according to geographical conditions; the emission frequency range of the emission source is determined; the environmental noise and the internal noise of the receiving system are measured to obtain the total noise of the receiving system; the minimum induced voltage of the receiving system is determined; the maximum induced voltage of the receiving system is determined; the minimum value of the electromagnetic response excited by the field source at the receiving position and the maximum value of the electromagnetic response excited by the field source at the receiving position are calculated; the maximum and minimum values ​​of the three components of the electromagnetic response are calculated; the minimum emission electric dipole moment and the maximum emission electric dipole moment are calculated; and the emission current range of the emission source is determined according to the maximum emission electric dipole moment and the minimum emission electric dipole moment. The arrangement of field sources that are adapted to the field environment and have a low-cost, high-efficiency, and accurate detection range is achieved.

Description

Technical Field

[0001] The invention belongs to the field of electromagnetic detection, and is particularly suitable for a ground-to-space frequency domain electromagnetic near-frequency dual-angle field source layout and parameter design method for exploration in areas with complex surface environments. Background Art

[0002] The ground-to-air frequency domain dipole electromagnetic detection method is a geophysical exploration method that uses the differences in the electromagnetic waves excited by the excitation device during the propagation of different media to cause differences in the induced voltage signals obtained by the receiving system, thereby distinguishing underground structures. It does not damage surface vegetation and underground structures, and is widely used in geological structure exploration, mineral resource search, natural disaster prevention and other aspects due to its non-contact and high reliability advantages. Compared with traditional electromagnetic detection methods, the artificial field source dipole electromagnetic detection method has higher detection accuracy and resolution, and can effectively detect subtle changes in underground media.

[0003] CN116088059A discloses an artificial source frequency domain electromagnetic exploration method and system based on dual-source staggered frequency transmission. The method uses two orthogonal field sources to transmit signals of different frequency combinations by staggered frequency to achieve three-dimensional apparent resistivity data acquisition in the target area. It can effectively distinguish electromagnetic response signals in different directions, thereby providing detailed underground structure information. However, there is a risk of signal interference. The staggered frequency design requires precise control. If the signal frequency is not properly selected, it may cause interference between different signals and affect the data quality. In addition, its equipment layout is complex. The system requires precise field source layout, especially in areas with complex terrain. The difficulty of layout increases, which may affect the accuracy of data acquisition.

[0004] CN116088060A discloses an orthogonal field source-staggered frequency excitation artificial source electromagnetic exploration system and method, which uses two orthogonal field sources to emit high-order pseudo-random signals, covering the entire frequency band range, and realizes the acquisition of three-dimensional electromagnetic data and the separation of polarization modes through staggered frequency excitation. This method is particularly suitable for exploration in complex geological environments. However, its synchronization control is difficult, and the system has strict requirements on synchronization control. Any synchronization problem may lead to inconsistent data. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a ground-to-space frequency domain electromagnetic near-frequency dual-angle field source layout and parameter design method to solve the problem of low accuracy and efficiency in detecting deep underground abnormal body structures.

[0006] The present invention is achieved in this way.

[0007] A method for ground-to-air frequency domain electromagnetic near-frequency dual-angle field source layout and parameter design, the method comprising:

[0008] Two transmitting sources are deployed according to geographical conditions;

[0009] Measure the average resistivity level of the observation area, and determine the emission frequency range of one of the emission sources based on the average apparent resistivity level and the detection target depth;

[0010] According to the emission frequency range of one emission source, the adjacent emission frequency of the second emission source is determined, so that the emission frequency of one emission source differs from the adjacent emission frequency of the second emission source in the range of 0%-5%, excluding 0%;

[0011] The total noise of the receiving system is obtained by measuring the environmental noise and the internal noise of the receiving system; the induced voltage of the receiving system is greater than or equal to the total noise of the receiving system. and noise threshold coefficient The product of , determine the minimum induced voltage of the receiving system; according to the range of the receiving system , so that the induced voltage of the receiving system is less than the range of the receiving system, and the maximum induced voltage of the receiving system is determined; according to the minimum induced voltage of the receiving system and the maximum induced voltage of the receiving system, the minimum value of the electromagnetic response excited by the field source at the receiving position and the maximum value of the electromagnetic response excited by the field source at the receiving position are calculated;

[0012] Calculate the maximum and minimum values ​​of the three components of the electromagnetic response according to the minimum induced voltage of the receiving system and the maximum induced voltage of the receiving system;

[0013] The minimum emission electric dipole moment and the maximum emission electric dipole moment are calculated according to the maximum and minimum values ​​of the three components of the electromagnetic response and the maximum and minimum values ​​of the electromagnetic response excited by the field source at the receiving position;

[0014] The range of the emission current of the emission source is determined according to the maximum emission electric dipole moment and the minimum emission electric dipole moment.

[0015] Furthermore, the average resistivity level of the observation area is measured, and the emission frequency range of one of the emission sources is determined according to the average apparent resistivity level and the detection target depth, including:

[0016] The current electrodes and potential electrodes are arranged in the observation area according to the selected electrode arrangement. The current is applied to the ground through the current electrodes. The potential difference generated is measured through the potential electrodes. The resistivity is calculated based on the measured potential difference and current:

[0017] ,

[0018] in: is the electrode spacing, is the potential difference, is the applied current, and the measured resistivity is averaged to obtain the average resistivity level ;

[0019] Estimate the frequency range of one of the sources:

[0020] ,

[0021] In the formula, To estimate the target emission frequency; is the target detection depth, which is an estimated range.

[0022] Furthermore, the two emission sources are in separate forms.

[0023] Furthermore, the maximum and minimum values ​​of the three components of the electromagnetic response are calculated according to the minimum induced voltage of the receiving system and the maximum induced voltage of the receiving system. The calculation formula is:

[0024] ,

[0025] in, is the induced voltage of the receiving system, which is a range value. For the receiving system The magnetic sensitivity coefficient on the component, is the transmitting frequency, for , express The electromagnetic response of the component.

[0026] Furthermore, the calculation formula for the minimum value of the electromagnetic response excited by the field source at the receiving position and the maximum value of the electromagnetic response excited by the field source at the receiving position is: , represents the average magnetic sensitivity coefficient of each component of the receiving system, Pick When , the minimum value of the electromagnetic response excited by the field source at the receiving position is obtained. Pick When , the maximum value of the electromagnetic response excited by the field source at the receiving position is obtained.

[0027] Further, the minimum emission electric dipole moment and the maximum emission electric dipole moment are calculated according to the maximum and minimum values ​​of the three components of the electromagnetic response and the maximum value of the electromagnetic response excited by the field source at the receiving position and the minimum value of the electromagnetic response excited by the field source at the receiving position, including:

[0028] By comparing the minimum value of the electromagnetic response excited by the field source at the receiving position with the maximum value of the Z component of the electromagnetic response, we can get The minimum emission moment of the component;

[0029] Calculate all lines The minimum emission moment of the component and the maximum value are obtained to obtain the The minimum emission moment of the component;

[0030] Similarly, we can get The minimum emission moment of the component and the observation area The minimum emission moment of the component; take the maximum value of the minimum emission moments of the three components to obtain the minimum emission moment of the observation area;

[0031] According to the maximum value of the electromagnetic response excited by the field source at the receiving position and the electromagnetic response The minimum value of the component is compared to obtain The maximum emission moment of the component;

[0032] Calculate all lines The maximum emission moment of the component and the minimum value are obtained to obtain the The maximum emission moment of the component;

[0033] Similarly, we can get The maximum emission moment of the component and the observation area The maximum emission moment of the component; take the minimum value of the maximum emission moment of the three components to obtain the maximum emission moment of the observation area;

[0034] The range of the emission current is determined according to the minimum emission moment and the maximum emission moment of the observation area.

[0035] Furthermore, the maximum and minimum deployment radius of the emission source from the observation area are calculated based on the minimum emission electric moment and the maximum emission electric moment of the observation area; according to the geographical conditions of the deployment of the field source, the deployment radius of the two emission sources and the distance between the two emission sources are adjusted so that the observation area is located in the intersection area of ​​the observation strong areas generated by the two emission sources.

[0036] Compared with the prior art, the present invention has the following beneficial effects: the present invention determines the combination of field sources according to the detection depth to be detected and the actual geographical environment, confirms the field source layout area according to the on-site field environment, determines the noise level of the measurement area by on-site equipment measurement, and then determines the range of the emission frequency according to geological information, and finally determines the emission electric dipole moment and emission current, thereby realizing the layout of field sources that adapt to the field environment and have a low-cost, high-efficiency and accurate detection range. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 A schematic diagram of the relationship between the observation area and the locations of two emission sources provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0039] A method for ground-to-air frequency domain electromagnetic near-frequency dual-angle field source layout and parameter design, the method comprising:

[0040] Two transmitting sources are deployed according to geographical conditions;

[0041] Measure the average resistivity level of the observation area, and determine the emission frequency range of one of the emission sources based on the average apparent resistivity level and the detection target depth;

[0042] According to the emission frequency range of one emission source, the adjacent emission frequency of the second emission source is determined, so that the emission frequency of one emission source differs from the adjacent emission frequency of the second emission source in the range of 0%-5%, excluding 0%, and the emission frequencies of the two emission sources are close but not the same;

[0043] The total noise of the receiving system is obtained by measuring the environmental noise and the internal noise of the receiving system; the induced voltage of the receiving system is greater than or equal to the total noise of the receiving system. and noise threshold coefficient The product of , determine the minimum induced voltage of the receiving system; according to the range of the receiving system , so that the induced voltage of the receiving system is less than the range of the receiving system, and the maximum induced voltage of the receiving system is determined; according to the minimum induced voltage of the receiving system and the maximum induced voltage of the receiving system, the minimum value of the electromagnetic response excited by the field source at the receiving position and the maximum value of the electromagnetic response excited by the field source at the receiving position are calculated;

[0044] Calculate the maximum and minimum values ​​of the three components of the electromagnetic response according to the minimum induced voltage of the receiving system and the maximum induced voltage of the receiving system;

[0045] The minimum emission electric dipole moment and the maximum emission electric dipole moment are calculated according to the maximum and minimum values ​​of the three components of the electromagnetic response and the maximum and minimum values ​​of the electromagnetic response excited by the field source at the receiving position;

[0046] The range of the emission current of the emission source is determined according to the maximum emission electric dipole moment and the minimum emission electric dipole moment.

[0047] The present invention determines the layout area of ​​the field source, selects an appropriate detection angle and determines the layout area of ​​the field source according to the actual situation on site, and first determines the general orientation of the two emission sources according to the observation area and external geographical conditions. A rectangular coordinate system is established with the target observation area as the center point to determine the angle within which the dual field source layout meets the geographical conditions for the layout of the field source. The observation area is located at the intersection of the two field source intensity areas.

[0048] Under the premise of not affecting the emission effect and meeting the emission detection requirements, the two emission sources should be arranged as close as possible, but the distance between them should generally not exceed 5km. As a preferred implementation, when designing the emission frequencies of the two emission sources, the frequency types of the field sources should be as many as possible and the selection of each frequency point should avoid power frequency interference signals, so as to ensure a high signal sampling rate. In order to meet the requirement that the two emission sources can emit at the same time, the emission frequencies of the two emission sources should be similar but not the same, and the difference between the two should be between 5% and 10%.

[0049] Measure the average resistivity level of the observation area, and determine the emission frequency range of one of the emission sources based on the average apparent resistivity level and the detection target depth, including:

[0050] The current electrodes and potential electrodes are arranged in the observation area according to the selected electrode arrangement. The current is applied to the ground through the current electrodes. The potential difference generated is measured through the potential electrodes. The resistivity is calculated based on the measured potential difference and current:

[0051] ,

[0052] in: is the electrode spacing, V is the potential difference, I is the applied current, and the measured resistivity is averaged to obtain the average resistivity level ;

[0053] Estimate the frequency range of one of the sources:

[0054] ,

[0055] In the formula, To estimate the target emission frequency; is the target detection depth, which is an estimated range.

[0056] The emission band of the source is determined by the known or inferred target detection depth. The emission band of the source is determined according to the resistivity properties and burial depth of the abnormal body. If the geological data is known, the specific burial depth of the known abnormal body can be substituted into Calculation is performed to determine the maximum transmission frequency and transmission frequency point.

[0057] The two emission sources of the present invention can be used separately or in a detection mode where different frequencies work simultaneously. For example, when 16 Hz is emitted in the x direction, 16.5 Hz with a frequency very close to that in the x direction is emitted in the y direction at the same time. This ensures that the error between the two frequencies is less than 5%-10%. In this way, when an abnormal body with a frequency greater than 5%-10% is found, the observation effect is better.

[0058] The total noise of the receiving system is obtained by measuring the environmental noise and the internal noise of the receiving system; the induced voltage of the receiving system is greater than or equal to the total noise of the receiving system. and noise threshold coefficient The product of , determine the minimum induced voltage of the receiving system; according to the range of the receiving system , so that the induced voltage of the receiving system is less than the range of the receiving system, and the maximum induced voltage of the receiving system is determined; according to the minimum induced voltage of the receiving system and the maximum induced voltage of the receiving system, the minimum value of the electromagnetic response excited by the field source at the receiving position and the maximum value of the electromagnetic response excited by the field source at the receiving position are calculated, specifically including:

[0059] It is known that the induced voltage of the receiving system has the following relationship with the electromagnetic response excited by the field source at the receiving position:

[0060] ,

[0061] in, is the induced voltage of the receiving system, is the average magnetic sensitivity coefficient of each component of the receiving system, which is determined by its sensor and circuit parameters. The electromagnetic response to the field source excitation at the receiving location.

[0062] Because the voltage of the total noise of the receiving system is equal to the ambient noise and system internal noise The sum of:

[0063] ,

[0064] In order to receive a valid signal, the induced voltage of the receiving system satisfies the following relationship:

[0065] ,

[0066] in, is the total noise of the receiving system, is the noise threshold coefficient.

[0067] From the mathematical expression of Faraday's law of electromagnetic induction:

[0068] ,

[0069] in, represents the number of turns of the receiving coil, represents the magnetic flux through the receiving coil, represents the gain of the preamplifier, represents the induced electromotive force, It represents the rate of change of magnetic flux. Represents the area of ​​a single turn of the coil. Indicates signal The amplitude of the component magnetic field is converted into Transformed to the frequency domain, the signal response formula for frequency detection can be obtained:

[0070] ,

[0071] Among them, For the receiving system The magnetic sensitivity coefficient on the component, is the transmitting frequency, for , express The electromagnetic response of the component. It can be obtained:

[0072] ,

[0073] The induced voltage of the receiving system should be greater than the total noise of the receiving system Smaller than the range of the receiving system ,Right now:

[0074] ,

[0075] Make the induced voltage of the receiving system greater than or equal to the total noise of the receiving system and noise threshold coefficient The product of , determine the minimum induced voltage of the receiving system; according to the range of the receiving system , so that the induced voltage of the receiving system is less than the range of the receiving system, determine the maximum induced voltage of the receiving system; according to the minimum induced voltage of the receiving system and the maximum induced voltage of the receiving system, according to the formula: , Pick When , the minimum value of the electromagnetic response excited by the field source at the receiving position is obtained. Pick When , the maximum value of the electromagnetic response excited by the field source at the receiving position is obtained.

[0076] And according to the formula: ,

[0077] Get electromagnetic response The maximum and minimum values ​​of the components, the electromagnetic response Maximum and minimum values ​​of components and electromagnetic response The maximum and minimum values ​​of the component.

[0078] By comparing the minimum value of the electromagnetic response excited by the field source at the receiving position with the maximum value of the Z component of the electromagnetic response, we can get The minimum emission moment of the component;

[0079] Calculate all lines The minimum emission moment of the component and the maximum value are obtained to obtain the The minimum emission moment of the component;

[0080] Get the observed area The minimum emission moment of the component and the observation area The minimum emission moment of the component; take the maximum value of the minimum emission moments of the three components to obtain the minimum emission moment of the observation area;

[0081] According to the maximum value of the electromagnetic response excited by the field source at the receiving position and the electromagnetic response The minimum value of the component is compared to obtain The maximum emission moment of the component;

[0082] Calculate all lines The maximum emission moment of the component and the minimum value are obtained to obtain the The maximum emission moment of the component;

[0083] Similarly, we can get The maximum emission moment of the component and the observation area The maximum emission moment of the component; take the minimum value of the maximum emission moment of the three components to obtain the maximum emission moment of the observation area;

[0084] The range of the emission current is determined according to the minimum emission moment and the maximum emission moment of the observation area.

[0085] The maximum transmitting electric moment is obtained by comparing the maximum value of the electromagnetic response excited by the field source at the receiving position with the Z component of the electromagnetic response;

[0086] Calculate the maximum emission moment of all survey lines and take the maximum value to obtain the maximum emission moment of the observation area;

[0087] The range of the emission current is determined according to the minimum emission moment and the maximum emission moment of the observation area.

[0088] The maximum and minimum deployment radius of the emission source from the observation area are calculated based on the minimum emission moment and the maximum emission moment of the observation area. Here, the relationship between the emission moment and the emission distance in the prior art can be used to calculate the maximum emission distance between the observation area and the emission source based on the minimum emission moment of the observation area, and the maximum emission distance is the maximum deployment radius; similarly, the minimum emission distance between the observation area and the emission source is calculated based on the maximum emission moment of the observation area, and the minimum emission distance is the minimum deployment radius; according to the geographical conditions of the deployment field source, the deployment radius of the two emission sources and the distance between the two emission sources are adjusted so that the observation area is located in the intersection area of ​​the observation strong areas generated by the two emission sources.

[0089] Through the above process, we can infer the deployment radius, transmission current and transmission frequency of the two transmission sources according to the observation area. When deploying the transmission source, the location of the transmission source is not unique. It only needs to be arranged within the range of the deployment radius and transmission current, combined with the geographical location, and ensure that the observation area is within the intersection of the observation strong areas generated by the two transmission sources. Figure 1 As shown, a rectangular coordinate system is made with two emission sources as the center, which is divided into the first quadrant, the second quadrant, the third quadrant and the fourth quadrant. The emission source has a strong observation area in each quadrant. It is necessary to arrange the observation area so that it is located in the intersection area of ​​the strong observation areas generated by the two emission sources.

[0090] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for ground-to-air frequency domain electromagnetic near-frequency dual-angle field source layout and parameter design, characterized in that: The method includes: Two transmitting sources are deployed according to geographical conditions; Measure the average resistivity level of the observation area, and determine the emission frequency range of one of the emission sources based on the average apparent resistivity level and the detection target depth; According to the emission frequency range of one emission source, the adjacent emission frequency of the second emission source is determined, so that the emission frequency of one emission source differs from the adjacent emission frequency of the second emission source in the range of 0%-5%, excluding 0%; The total noise of the receiving system is obtained by measuring the environmental noise and the internal noise of the receiving system; the induced voltage of the receiving system is greater than or equal to the total noise of the receiving system. and noise threshold coefficient The product of , determine the minimum induced voltage of the receiving system; according to the range of the receiving system , so that the induced voltage of the receiving system is less than the range of the receiving system, and the maximum induced voltage of the receiving system is determined; according to the minimum induced voltage of the receiving system and the maximum induced voltage of the receiving system, the minimum value of the electromagnetic response excited by the field source at the receiving position and the maximum value of the electromagnetic response excited by the field source at the receiving position are calculated; Calculate the maximum and minimum values ​​of the three components of the electromagnetic response according to the minimum induced voltage of the receiving system and the maximum induced voltage of the receiving system; The minimum emission electric dipole moment and the maximum emission electric dipole moment are calculated according to the maximum and minimum values ​​of the three components of the electromagnetic response and the maximum and minimum values ​​of the electromagnetic response excited by the field source at the receiving position; The range of the emission current of the emission source is determined according to the maximum emission electric dipole moment and the minimum emission electric dipole moment.

2. The method for ground-to-air frequency domain electromagnetic near-frequency dual-angle field source layout and parameter design according to claim 1 is characterized in that: Measure the average resistivity level of the observation area, and determine the emission frequency range of one of the emission sources based on the average apparent resistivity level and the detection target depth, including: The current electrodes and potential electrodes are arranged in the observation area according to the selected electrode arrangement. The current is applied to the ground through the current electrodes. The potential difference generated is measured through the potential electrodes. The resistivity is calculated based on the measured potential difference and current: ， in: is the electrode spacing, is the potential difference, is the applied current, and the measured resistivity is averaged to obtain the average resistivity level ; Estimate the frequency range of one of the sources: ， In the formula, To estimate the target emission frequency; is the target detection depth, which is an estimated range.

3. The method for ground-to-air frequency domain electromagnetic near-frequency dual-angle field source layout and parameter design according to claim 1 is characterized in that: The two emission sources are in separate forms.

4. The method for ground-to-air frequency domain electromagnetic near-frequency dual-angle field source layout and parameter design according to claim 1 is characterized in that: The maximum and minimum values ​​of the three components of the electromagnetic response are calculated based on the minimum induced voltage of the receiving system and the maximum induced voltage of the receiving system. The calculation formula is: ， in, is the induced voltage of the receiving system, which is a range value. For the receiving system The magnetic sensitivity coefficient on the component, is the transmitting frequency, for , express The electromagnetic response of the component.

5. The method for ground-to-air frequency domain electromagnetic near-frequency dual-angle field source layout and parameter design according to claim 4 is characterized in that: The calculation formula of the minimum value of the electromagnetic response excited by the field source at the receiving position and the maximum value of the electromagnetic response excited by the field source at the receiving position is: , represents the average magnetic sensitivity coefficient of each component of the receiving system, Pick When , the minimum value of the electromagnetic response excited by the field source at the receiving position is obtained. Pick When , the maximum value of the electromagnetic response excited by the field source at the receiving position is obtained.

6. The method for ground-to-air frequency domain electromagnetic near-frequency dual-angle field source layout and parameter design according to claim 5 is characterized in that: The minimum emission electric dipole moment and the maximum emission electric dipole moment are calculated based on the maximum and minimum values ​​of the three components of the electromagnetic response and the maximum and minimum values ​​of the electromagnetic response excited by the field source at the receiving position, including: By comparing the minimum value of the electromagnetic response excited by the field source at the receiving position with the maximum value of the Z component of the electromagnetic response, we can get The minimum emission moment of the component; Calculate all lines The minimum emission moment of the component and the maximum value are obtained to obtain the The minimum emission moment of the component; Similarly, we get The minimum emission moment of the component and the observation area The minimum emission moment of the component; take the maximum value of the minimum emission moments of the three components to obtain the minimum emission moment of the observation area; According to the maximum value of the electromagnetic response excited by the field source at the receiving position and the electromagnetic response The minimum value of the component is compared to obtain The maximum emission moment of the component; Calculate all lines The maximum emission moment of the component and the minimum value are obtained to obtain the The maximum emission moment of the component; Similarly, we get The maximum emission moment of the component and the observation area The maximum emission moment of the component; take the minimum value of the maximum emission moment of the three components to obtain the maximum emission moment of the observation area; The range of the emission current is determined according to the minimum emission moment and the maximum emission moment of the observation area.

7. The method for ground-to-air frequency domain electromagnetic near-frequency dual-angle field source layout and parameter design according to claim 6 is characterized in that: The maximum and minimum deployment radius of the emission source from the observation area are calculated based on the minimum emission electric moment and the maximum emission electric moment of the observation area; according to the geographical conditions of the deployment source, the deployment radius of the two emission sources and the distance between the two emission sources are adjusted so that the observation area is located in the intersection area of ​​the observation strong areas generated by the two emission sources.

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