Self-adaptive regulation and control system and method for magnetotelluric sounding observation duration in salt lake low-resistance area

Abstract

The invention discloses a salt lake low-resistance area magnetotelluric sounding observation duration adaptive regulation and control system and method, and relates to the technical field of geophysical exploration, and the method comprises the steps: selecting a measurement point before observation starting, collecting an electric field and geomagnetic time sequence in real time, calculating the change rate indexes of an electric field and a magnetic field, and obtaining the overall stability index of an electromagnetic field; establishing a first stable time period through threshold judgment, and starting observation pre-activation and interference source analysis; arranging a magnetic induction coil array based on the first stable time period, calculating electric field noise energy density and direction interference index in each direction, screening a low interference direction and locking a main observation direction; acquiring an electric field component in a main direction in real time, calculating effective electric field intensity, comparing the effective electric field intensity with a low-resistance penetration threshold value, judging the penetration capability, and determining whether to start a delay acquisition mechanism or not; comprehensively constructing an observation weighting factor, and correcting the final acquisition time; according to the method, the observation data quality and stability in the salt lake area low-resistance environment are effectively improved, and effective acquisition of deep electromagnetic response is ensured.

Description

Technical Field

[0001] This invention relates to the field of geophysical exploration technology, specifically to an adaptive control system and method for magnetotelluric sounding duration in low-resistivity salt lake areas. Background Technology

[0002] Magnetotelluric (MT) sounding is a passive detection technique that uses natural electromagnetic field sources to obtain information on the electrical structure of the subsurface. It is widely used in geological surveys, mineral exploration, and geothermal resource research. However, conducting MT observations in highly saline areas, especially in saline lake basins and low-lying evaporation environments, often faces the following three technical challenges: The underground brine results in extremely low resistivity, creating a "low-resistivity shielding" effect. High-mineralization brine is widely present in the strata of the salt lake area, and the underground resistivity is significantly lower than in other areas (can be lower than 1). The low density (·m) causes the natural electromagnetic field to dissipate severely in shallow layers, making it difficult to excite deep responses. This results in shallow inversion depths, strong signal attenuation, and difficulty in identifying target strata, becoming the primary obstacle to MT detection in salt lakes.

[0003] Natural electromagnetic fields vary dramatically, making stable observation difficult. As a passive method, MT measurements rely on the Earth's natural electromagnetic field. However, in practical applications, especially at night, during periods of strong weather interference, or when the ionosphere is unstable, the amplitude of electric and magnetic fields varies greatly, resulting in poor stability and severe fluctuations in long-period signals. This leads to difficulties in selecting observation windows and poor data consistency.

[0004] Strong interference sources cause severe interference, making it difficult to guarantee data quality. Salt lake areas are usually close to mining areas, highways, power grids and industrial facilities, and are widely affected by man-made power interference, power frequency interference (50Hz), geomagnetic storms and other events. The superimposed effects can cause the geoelectric field signal to jump, pseudo-periodic or frequency domain pollution, reducing the accuracy of data acquisition and the reliability of subsequent inversion.

[0005] To address the aforementioned issues, traditional MT observation methods often employ fixed-time and fixed-direction acquisition strategies, which cannot dynamically respond to fluctuations or changes in field sources or interference. This can easily lead to the acquisition of invalid data when the field source is unstable or when directional interference is significant, resulting in wasted time and insufficient detection depth, making it difficult to meet the high-quality detection requirements in complex electrical environments. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides an adaptive control system and method for magnetotelluric sounding duration in low-resistivity salt lake areas, in order to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: an adaptive control system and method for magnetotelluric sounding duration in low-resistivity salt lake areas, comprising the following steps: Step 1: In the observation preparation stage before the start of the magnetotelluric sounding observation, select electric field measuring points within the survey line area of ​​the salt lake area, and collect the east-west electric field time series Ex(t) and the north-south electric field time series Ey(t) of the target measuring points in real time; deploy a triaxial induction coil magnetometer to collect the high-resolution geomagnetic field north-south component series Hx(t), east-west component series Hy(t), and vertical component series Hz(t) in real time; install a synchronous electromagnetic field observation device to record the initial stable values ​​of the local reference electric field E0 and magnetic field H0; Step 2: Calculate and obtain the electric field change rate index SE and the magnetic field change rate index SH, and further calculate and obtain the overall electromagnetic field stability index Gt. Compare and analyze these with the change rate threshold Qbh and the overall electromagnetic field stability threshold Qdw to determine whether the current electromagnetic field is in a stable state and establish the first stable period. If it is in a stable state, enter the observation pre-activation state and start the interference source analysis mechanism; if it is unstable, provide a strategy. Step 3: After identifying the first stable period, select electric field measuring points along the survey line in the salt lake area, deploy a geomagnetic induction coil array, and acquire the original time series signal E. (t), and calculate the power spectral density. Electric field noise energy density N in unit direction Further calculations were performed to obtain the directional interference index (GRD) for each direction. The values ​​are evaluated against the directional interference threshold Qfg, and a set of low-interference directions is established; the minimum value is selected. The direction selection coefficient Gd is calculated and compared with the direction selection threshold Qsx to lock the current direction as the main observation direction. Step 4: Along the locked main observation direction, collect the electric field component sequence in real time using the ground electric field sensors deployed along the main observation direction. Calculate and obtain the effective electric field strength value The data is compared with the low-resistivity penetration threshold Eth to determine whether the observation conditions meet the penetration capability requirements. If they do, the final acquisition duration monitoring mechanism is activated; otherwise, a strategy is provided. Step 5: By combining the overall electromagnetic field stability index Gt, the direction selection coefficient Gd, and the effective electric field strength value Construct observation weighting factors The final observation time Tfinal is then calculated.

[0008] Preferably, step one includes: S11. Before the commencement of magnetotelluric sounding observation, electric field measuring points were selected within the survey line area of ​​the salt lake region. Two pairs of non-polarized electrodes were symmetrically buried along the east-west and north-south directions, respectively. The electrode spacing was set at 50 meters and the burial depth at 20 centimeters. A horizontal dipole was constructed and connected to a low-noise electric field amplifier and a high-precision data acquisition device. The real-time acquisition of the horizontal electric field time series in two directions of the ground electric field included: the east-west electric field time series Ex(t) and the north-south electric field time series Ey(t). S12. At a distance of 15 meters from the electric field measurement, a triaxial induction coil magnetometer is laid out along the east-west, north-south and vertical directions respectively, and high-resolution geomagnetic field north-south component sequence Hx(t), east-west component sequence Hy(t) and vertical component sequence Hz(t) are collected in real time. S13. Set up a continuous reference measuring point within 3 kilometers of the target observation point, install a synchronous electromagnetic field observation device, and record the initial stable values ​​of the local reference electric field E0 and magnetic field H0.

[0009] Preferably, step two includes: S21. Obtain the rate of change of the electric field at the target observation point by using the moving average difference smoothing differentiation technique on the time series of the horizontal electric field in two directions of the ground electric field Ex(t) and Ey(t). By approximating the derivatives of the high-resolution geomagnetic field north-south component sequence Hx(t), east-west component sequence Hy(t), and vertical component sequence Hz(t) at each time point using numerical differentiation algorithms such as central difference, the rate of change of the geomagnetic field at the target observation point is obtained. ; S22. Based on the rate of change of the electric field at the target observation point and the rate of change of the geomagnetic field at the target observation point By combining the initial stable values ​​of the reference electric field E0 and the initial stable value of the magnetic field H0, and after dimensionless processing, the electric field rate of change exponent SE and the magnetic field rate of change exponent SH are calculated and obtained respectively.

[0010] S23. By combining the electric field rate of change index SE and the magnetic field rate of change index SH, and after dimensionless processing, the overall electromagnetic field stability index Gt is calculated and obtained.

[0011] Preferably, step two also includes: S24. By setting a change rate threshold Qbh and an overall electromagnetic field stability threshold Qdw, and comparing the electric field change rate index SE and the magnetic field change rate index SH with the change rate threshold Qbh, and comparing the overall electromagnetic field stability index Gt with the overall electromagnetic field stability threshold Qdw, the first evaluation results are obtained, including: When the electric field rate of change exponent SE ≤ the rate of change threshold Qbh, the magnetic field rate of change exponent SH ≤ the rate of change threshold Qbh, and at the same time the electromagnetic field overall stability exponent Gt ≥ the electromagnetic field overall stability threshold Qdw, it indicates that the current electromagnetic field is in a stable state, which is recorded as the "first stable period". The observation pre-activation state is entered and the interference source analysis mechanism is started. When either the electric field rate of change index SE or the magnetic field rate of change index SH is greater than the rate of change threshold Qbh, or when the overall electromagnetic field stability index Gt is less than the overall electromagnetic field stability threshold Qdw, it indicates that the current electromagnetic field is in an unstable state, triggering the first warning command and generating the first strategy: automatically execute the observation suspension command, enter the waiting state, and reassess the next time window once every 5 minutes at a set time interval.

[0012] Preferably, step three includes: S31. After identifying the "first stable period", select electric field measurement points on the survey line in the salt lake area, and with the center as the base point, rotate and deploy the geomagnetic induction coil array every 15° according to the polar coordinate angle to complete the deployment of the induction measurement array in 12 directions. S32. During the first stable period, a synchronous acquisition device is used to record the electric field noise data corresponding to each direction, and the original time series signal E is obtained. (t), and then perform segmented windowing processing, and then use Fast Fourier Transform (FFT) on each segment of the signal to extract the energy distribution on each frequency component and obtain the spectrum of the signal. S33. The Welch averaging method is used to perform squared averaging on the FFT results of each segment. After dimensionless processing, the power spectral density is constructed. ; S34, via power spectral density A frequency band is defined, and the power spectral density within the band is integrated. After dimensionless processing, the electric field noise energy density N per unit direction is calculated. ; S35. Utilize Fast Fourier Transform (FFT) technology to analyze the electric field spectrum in each direction, identify the spectral energy within the range of 50Hz ± 1Hz, and calculate its proportion of the total energy, which is used as the main power frequency interference weighting factor W in the current direction. .

[0013] Preferably, step three also includes: S36, The electric field noise energy density N obtained in unit direction and main power frequency interference weighting factor W After dimensionless processing, the directional interference index GRD for each direction is calculated and obtained. ; S37. By traversing all set observation directions and setting a direction interference threshold Qfg, and comparing it with the direction interference index GRD for each direction. Comparative analysis was conducted to select all those that meet the GRD criteria. The direction ≤Qfg is determined, and a set of low-interference directions is established; the directional interference index GRD is selected from the set of low-interference directions. Minimum value The direction is taken as the optimal principal axis direction.

[0014] Preferably, step three also includes: S38. Quantitative evaluation is performed using the optimal principal axis direction. After dimensionless processing, the direction selection coefficient Gd is calculated and obtained.

[0015] S39. By setting a directional screening threshold Qsx, and comparing and analyzing the directional screening coefficient Gd with the directional screening threshold Qsx, the second evaluation result is obtained, including: When the direction selection coefficient Gd ≥ the direction selection threshold Qsx, it means that there is no directional interference in the current observation window, the current direction is locked as the main observation direction, and the delayed acquisition and control stage is entered. When the directional screening coefficient Gd < the directional screening threshold Qsx, it indicates that there is directional interference in the current observation window, triggering the second early warning instruction and generating the second strategy: temporarily not enter the acquisition process; automatically postpone the decision and wait for the next "new stable period" that meets the field strength stability to carry out directional deployment and interference assessment again, until the directional screening coefficient Gd ≥ the directional screening threshold Qsx.

[0016] Preferably, step four includes: S41. On the locked main observation direction, the electric field component sequence is acquired in real time by using the ground electric field sensor deployed on the main observation direction. ; S42. Extraction using the envelope averaging method The instantaneous envelope of the electric field is calculated, and the average value is calculated within a time window of 10-30 seconds. After dimensionless processing using the root mean square method, the effective electric field strength value is obtained. ; S43. By setting a low-resistance penetration threshold Eth, the effective electric field strength value A comparative analysis with the low-resistance penetration threshold Eth yielded the following third evaluation results: When the effective electric field strength value When the value is ≥ the low-resistivity penetration threshold Eth, it indicates that the observation conditions meet the penetration capability requirements, and the device has the capability to effectively electromagnetically excite shallow low-resistivity structures. It will automatically enter the delayed observation stage and start the final acquisition duration monitoring mechanism. When the effective electric field strength value When the value is less than the low-resistivity penetration threshold Eth, it indicates that the observation conditions do not meet the penetration capability requirements and the ability to effectively electromagnetically excite shallow low-resistivity structures is not available. This triggers the third early warning instruction and generates the third strategy: do not activate the delayed observation mechanism, only maintain the basic observation duration for routine data acquisition, and mark the current time period as a non-enhanced excitation period, waiting for the natural field strength to increase in subsequent time windows before re-evaluating the effectiveness.

[0017] Preferably, step five includes: S51, By combining the overall electromagnetic field stability index Gt, the direction selection coefficient Gd, and the effective electric field strength value After dimensionless processing, an observation weighting factor is constructed. ; S52, By observing the weighting factors The basic observation time T0 is extended and adjusted, and after dimensionless processing, the final observation time Tfinal is calculated.

[0018] Preferred, an adaptive control system for magnetotelluric sounding duration in low-resistivity salt lake areas includes: The electromagnetic field basic acquisition module is used in the observation preparation stage before the start of magnetotelluric sounding. It selects electric field measurement points within the survey line area of ​​the salt lake area and acquires the east-west electric field time series Ex(t) and the north-south electric field time series Ey(t) of the target measurement points in real time. It also deploys a triaxial induction coil magnetometer to acquire the high-resolution geomagnetic field north-south component series Hx(t), east-west component series Hy(t), and vertical component series Hz(t) in real time. Finally, it installs a synchronous electromagnetic field observation device to record the initial stable values ​​of the local reference electric field E0 and magnetic field H0. The electromagnetic field stability monitoring module is used to calculate and obtain the electric field change rate index SE and the magnetic field change rate index SH, and further calculate and obtain the overall electromagnetic field stability index Gt. These are compared and analyzed with the change rate threshold Qbh and the overall electromagnetic field stability threshold Qdw to determine whether the current electromagnetic field is in a stable state and to establish the first stable period. If it is in a stable state, it enters the observation pre-activation state and starts the interference source analysis mechanism. If it is unstable, a strategy is given. The directional interference identification module is used to acquire the original time series signal E by selecting electric field measuring points along the survey line in the salt lake area and deploying a geomagnetic induction coil array after identifying the first stable period. (t), and calculate the power spectral density. Electric field noise energy density N in unit direction Further calculations were performed to obtain the directional interference index (GRD) for each direction. The values ​​are evaluated against the directional interference threshold Qfg, and a set of low-interference directions is established; the minimum value is selected. The direction selection coefficient Gd is calculated and compared with the direction selection threshold Qsx to lock the current direction as the main observation direction. The effective electric field penetration monitoring module is used to acquire electric field component sequences in real time along the locked main observation direction using ground electric field sensors deployed along that direction. Calculate and obtain the effective electric field strength value The data is compared with the low-resistivity penetration threshold Eth to determine whether the observation conditions meet the penetration capability requirements. If they do, the final acquisition duration monitoring mechanism is activated; otherwise, a strategy is provided. The final observation time correction module is used to combine the overall electromagnetic field stability index Gt, the direction selection coefficient Gd, and the effective electric field strength value. Construct observation weighting factors The final observation time Tfinal is then calculated.

[0019] This invention provides an adaptive control system and method for magnetotelluric sounding duration in low-resistivity salt lake areas. It offers the following advantages: (1) The adaptive control system and method for the duration of magnetotelluric sounding observation in the low resistivity area of ​​the salt lake introduces an electric field traction intensity assessment mechanism and sets a low resistivity penetration threshold to determine the observation energy. This can effectively identify observation opportunities with deep response value, thereby alleviating the "low resistivity shielding effect" caused by the extremely low resistivity of brine in the salt lake area and significantly improving the effective observation depth.

[0020] (2) The adaptive control system and method for the duration of magnetotelluric sounding observation in the low resistivity area of ​​the salt lake is to construct the electromagnetic field stability index, direction screening coefficient and observation weighting factor, and dynamically control the start and delay duration of observation based on the real-time electromagnetic fluctuation state, so as to realize intelligent control with "energy traction + environmental assessment" as the core, and improve the data density and inversion accuracy of each observation.

[0021] (3) The adaptive control system and method for the duration of magnetotelluric sounding observation in the low resistivity area of ​​the salt lake quantifies the electric field energy density and the main power frequency interference weight factor in each direction before the observation starts, constructs the directional interference index and sets the directional screening threshold, accurately identifies the low interference main observation direction, and effectively avoids the impact of industrial interference sources and human disturbances on the measurement accuracy.

[0022] (4) The adaptive control system and method for magnetotelluric sounding observation time in the low-resistivity area of ​​the salt lake, through the linkage design of stability judgment and delay control mechanism, enables the final observation time to adapt to the changes in the current natural field strength, directional interference and low-resistivity penetration potential, ensuring that the collected data covers high-value response sections and enhancing the credibility of the coupling relationship between data and underground structure. Attached Figure Description

[0023] Figure 1 This is a schematic diagram illustrating the steps of the adaptive adjustment method for magnetotelluric sounding duration in low-resistivity salt lake areas according to the present invention. Figure 2 This is a flowchart illustrating the adaptive control system for magnetotelluric sounding duration in low-resistivity salt lake areas according to the present invention. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Example 1 Please see Figure 1 This invention provides an adaptive control system and method for magnetotelluric sounding duration in low-resistivity salt lake areas, comprising the following steps: Step 1: In the observation preparation stage before the start of the magnetotelluric sounding observation, select electric field measuring points within the survey line area of ​​the salt lake area, and collect the east-west electric field time series Ex(t) and the north-south electric field time series Ey(t) of the target measuring points in real time; deploy a triaxial induction coil magnetometer to collect the high-resolution geomagnetic field north-south component series Hx(t), east-west component series Hy(t), and vertical component series Hz(t) in real time; install a synchronous electromagnetic field observation device to record the initial stable values ​​of the local reference electric field E0 and magnetic field H0; Step 2: Calculate and obtain the electric field change rate index SE and the magnetic field change rate index SH, and further calculate and obtain the overall electromagnetic field stability index Gt. Compare and analyze these with the change rate threshold Qbh and the overall electromagnetic field stability threshold Qdw to determine whether the current electromagnetic field is in a stable state and establish the first stable period. If it is in a stable state, enter the observation pre-activation state and start the interference source analysis mechanism; if it is unstable, provide a strategy. Step 3: After identifying the first stable period, select electric field measuring points along the survey line in the salt lake area, deploy a geomagnetic induction coil array, and acquire the original time series signal E. (t), and calculate the power spectral density. Electric field noise energy density N in unit direction Further calculations were performed to obtain the directional interference index (GRD) for each direction. The values ​​are evaluated against the directional interference threshold Qfg, and a set of low-interference directions is established; the minimum value is selected. The direction selection coefficient Gd is calculated and compared with the direction selection threshold Qsx to lock the current direction as the main observation direction. Step 4: Along the locked main observation direction, collect the electric field component sequence in real time using the ground electric field sensors deployed along the main observation direction. Calculate and obtain the effective electric field strength value The data is compared with the low-resistivity penetration threshold Eth to determine whether the observation conditions meet the penetration capability requirements. If they do, the final acquisition duration monitoring mechanism is activated; otherwise, a strategy is provided. Step 5: By combining the overall electromagnetic field stability index Gt, the direction selection coefficient Gd, and the effective electric field strength value Construct observation weighting factors The final observation time Tfinal is then calculated.

[0026] In this embodiment, by constructing a multi-factor dynamic control mechanism based on the electromagnetic field stability index, electric field traction capability, and directional interference index, it is possible to adaptively identify high-quality observation windows and main observation directions and dynamically adjust the observation duration in the environment of salt lake areas with severe natural field strength fluctuations and significant interference from shallow low resistivity. This significantly improves the ability to acquire deep responses and data quality, and enhances the adaptability and accuracy of magnetotelluric sounding in complex low-resistivity areas.

[0027] Example 2 This embodiment is an explanation of Embodiment 1. Specifically, step one includes: S11. Before the commencement of magnetotelluric sounding observation, electric field measuring points were selected within the survey line area of ​​the salt lake region. Two pairs of non-polarized electrodes were symmetrically buried along the east-west and north-south directions, respectively. The electrode spacing was set at 50 meters and the burial depth at 20 centimeters. A horizontal dipole was constructed and connected to a low-noise electric field amplifier and a high-precision data acquisition device. The real-time acquisition of the horizontal electric field time series in two directions of the ground electric field included: the east-west electric field time series Ex(t) and the north-south electric field time series Ey(t). S12. At a distance of 15 meters from the electric field measurement, a triaxial induction coil magnetometer is laid out along the east-west, north-south and vertical directions respectively, and high-resolution geomagnetic field north-south component sequence Hx(t), east-west component sequence Hy(t) and vertical component sequence Hz(t) are collected in real time. S13. Set up a continuous reference measuring point within 3 kilometers of the target observation point, install a synchronous electromagnetic field observation device, and record the initial stable values ​​of the local reference electric field E0 and magnetic field H0.

[0028] In this embodiment, by deploying bidirectional non-polarized electrodes and triaxial induction coil magnetometers in the early stage of observation, and setting up synchronous reference measurement points, a complete space electromagnetic observation system is constructed. This system can acquire the geoelectric and geomagnetic field components and their reference reference values ​​at the target measurement points in real time with high precision. This provides basic data support for subsequent electromagnetic field stability assessment, directional interference discrimination, and observation control, significantly improving the accuracy of electromagnetic signal acquisition and system reliability in the complex environment of the salt lake area.

[0029] Example 3 This embodiment is an explanation of embodiment 2. Specifically, step two includes: S21. Obtain the rate of change of the electric field at the target observation point by using the moving average difference smoothing differentiation technique on the time series of the horizontal electric field in two directions of the ground electric field Ex(t) and Ey(t). By approximating the derivatives of the high-resolution geomagnetic field north-south component sequence Hx(t), east-west component sequence Hy(t), and vertical component sequence Hz(t) at each time point using numerical differentiation algorithms such as central difference, the rate of change of the geomagnetic field at the target observation point is obtained. ; S22. Based on the rate of change of the electric field at the target observation point and the rate of change of the geomagnetic field at the target observation point Combining the initial stable values ​​of the reference electric field E0 and magnetic field H0, and after dimensionless processing, the electric field rate of change exponent SE and the magnetic field rate of change exponent SH are calculated and obtained respectively, as follows: ; ; S23. By combining the electric field rate of change index SE and the magnetic field rate of change index SH, and after dimensionless processing, the overall electromagnetic field stability index Gt is calculated as follows:

[0030] In this embodiment, by introducing the moving average difference smoothing differential technique and the central difference numerical algorithm, the rate of change of the time series of the geoelectric field and the geomagnetic field in multiple directions is extracted respectively. The electric field rate of change index SE and the magnetic field rate of change index SH are constructed by combining the initial stable reference values ​​E0 and H0, and finally the overall electromagnetic field stability index Gt is formed. This realizes the quantitative identification and dynamic evaluation of the field strength stability in the complex electromagnetic environment of the salt lake area, and provides technical support for the accurate prediction of high-quality observation windows.

[0031] Example 4 This embodiment is an explanation of embodiment 3. Specifically, step two also includes: S24. By setting a change rate threshold Qbh and an overall electromagnetic field stability threshold Qdw, and comparing the electric field change rate index SE and the magnetic field change rate index SH with the change rate threshold Qbh, and comparing the overall electromagnetic field stability index Gt with the overall electromagnetic field stability threshold Qdw, the first evaluation results are obtained, including: When the electric field rate of change exponent SE ≤ the rate of change threshold Qbh, the magnetic field rate of change exponent SH ≤ the rate of change threshold Qbh, and at the same time the electromagnetic field overall stability exponent Gt ≥ the electromagnetic field overall stability threshold Qdw, it indicates that the current electromagnetic field is in a stable state, which is recorded as the "first stable period". The observation pre-activation state is entered and the interference source analysis mechanism is started. When either the electric field rate of change index SE or the magnetic field rate of change index SH is greater than the rate of change threshold Qbh, or when the overall electromagnetic field stability index Gt is less than the overall electromagnetic field stability threshold Qdw, it indicates that the current electromagnetic field is in an unstable state, triggering the first warning command and generating the first strategy: automatically execute the observation suspension command, enter the waiting state, and reassess the next time window once every 5 minutes at a set time interval.

[0032] The method for setting the rate of change threshold Qbh is as follows: Based on the statistical research results of a large amount of electromagnetic field measurement data; through electromagnetic field time series analysis of several typical salt lake areas and adjacent high conductivity areas, the range of natural rate of change of electromagnetic waveforms under the condition of no sudden disturbances and equipment interference is extracted. Combining the experience standards used in the geophysical industry for evaluating the effectiveness of field observations, the upper limit of normal fluctuations is clearly defined as the baseline for judging the "stable" or "observable" state of the electromagnetic field; the setting of the threshold also refers to the following: typical noise tolerance data and dynamic response bandwidth provided by domestic and foreign electromagnetic detection instrument manufacturers; the definition of fluctuation amplitude of stable observation sections in the national standard "Geophysical Exploration Specification" (such as GB / T51246); the characteristics of typical rate of change value ranges and artificial interference sections caused by electromagnetic sources (such as diurnal variations, thunderstorms, and geomagnetic storms); the rate of change threshold Qbh is comprehensively set to 0.5; when the rate of change of electric field and magnetic field at the observation point is simultaneously lower than 0.5, it indicates that it is in a period of stable electromagnetic change; The overall stability threshold Qdw of the electromagnetic field is set as follows: Based on the joint evaluation index of the rate of change of the electric and magnetic fields, considering the largest disturbance term among the two, it is defined using a normalized complementary method: The introduction of this stability index aims to establish a unified dimensionless standard for determining whether the current observation environment is suitable for entering the formal data acquisition phase. The threshold setting is based on the following principles: 0.95 is used as the stability boundary, representing a rate of change of less than 5% (consistent with the aforementioned rate of change threshold), reflecting a high degree of electromagnetic stability; this value has been verified through comparison with a large number of field observation projects and is highly correlated with the lower limit of instrument noise, data quality, and interference risk level; at the same time, combined with the time period filtering mechanism in the "effective observation window selection algorithm," Gt≥0.95 becomes a high-confidence stability judgment standard.

[0033] In this embodiment, by setting the rate of change threshold Qbh and the overall stability threshold Qdw of the electromagnetic field, a multi-index joint judgment mechanism is established to dynamically evaluate the rate of change index of the electric field and the magnetic field and their overall stability index. This can accurately identify the stable state of the electromagnetic field and establish the "first stable period", effectively avoiding the problem of observation misjudgment caused by frequent electromagnetic disturbances in the salt lake area, and improving the start-up accuracy and interference prevention and control capabilities of the magnetotelluric sounding data acquisition stage.

[0034] Example 5 This embodiment is an explanation of embodiment 4. Specifically, step three includes: After completing the electromagnetic field stability assessment and identifying the "first stable period," the system immediately enters the directional interference identification and deployment path selection stage to further mitigate the potential impact of local directional interference on the quality of subsequent data acquisition. This stage uses the "first stable period" as the observation window and proactively constructs a multi-directional electromagnetic induction acquisition array. Through rotating induction deployment and synchronous observation technology, it accurately assesses the background noise and power frequency interference intensity in each direction, quantifies the directional interference risk, and then selects the observation axis direction with the least interference. This provides a low-interference deployment basis for subsequent delayed acquisition and adaptive observation duration adjustment, ensuring improved efficiency in acquiring useful signals and data reliability in a low-impedance shielded environment.

[0035] S31. After identifying the "first stable period", select electric field measurement points on the survey line in the salt lake area, and with the center as the base point, rotate and deploy the geomagnetic induction coil array every 15° according to the polar coordinate angle to complete the deployment of the induction measurement array in 12 directions. S32. During the first stable period, a synchronous acquisition device is used to record the electric field noise data corresponding to each direction, and the original time series signal E is obtained. (t), and then perform segmented windowing processing, and then use Fast Fourier Transform (FFT) on each segment of the signal to extract the energy distribution on each frequency component and obtain the spectrum of the signal. The power spectral density estimation uses the Welch averaging method, a common frequency domain analysis technique. Specifically, it involves averaging the electric field time series signal E in a specific direction. The signal is divided into several segments, and a window function such as a Hanning window is applied to each segment to reduce spectral leakage. Then, a Fast Fourier Transform (FFT) is performed on each segment to obtain its spectrum, which is then squared. The squared values ​​of all segmented spectra are then averaged to obtain a stable and reliable power spectral density curve, which is used to characterize the energy distribution of the electric field signal in that direction at each frequency. After obtaining the power spectral density, the spectral lines can be integrated according to a preset effective frequency range, such as 0.1–10Hz or 0.1–30Hz, specifically selected based on the magnetotelluric sounding frequency band, to obtain the noise energy density value of the electric field in that direction throughout the entire frequency band. This value reflects the total energy disturbance intensity of the natural background electric field in that direction, and is used to assess the magnitude of directional interference, providing a basis for subsequent selection of low-interference directions. S33. The Welch averaging method is used to perform squared averaging on the FFT results of each segment. After dimensionless processing, the power spectral density is constructed. The formula is as follows:

[0036] In the formula, N represents the number of segments. This represents the power value of the i-th signal segment at frequency f, which is the result of the fast Fourier transform of the i-th signal segment at frequency f. S34, via power spectral density A frequency band is defined, and the power spectral density within the band is integrated. After dimensionless processing, the electric field noise energy density N per unit direction is calculated. The formula is as follows:

[0037] In the formula, f1 represents the starting frequency, f2 represents the ending frequency, and df represents the frequency increment, which is a tiny frequency change unit during the integration process. Frequency band acquisition method: Through statistical analysis of a large amount of magnetotelluric (MT) measured data, covering different geological scenarios (such as saline lake areas, sedimentary basins, magmatic rock belts, etc.) and various typical natural field fluctuation conditions, the signal energy distribution characteristics within each frequency band are extracted. Combined with the frequency response range and sensitivity parameters of the electromagnetic field observation equipment, the ability of each frequency band to distinguish between effective signals and noise in actual acquisition is analyzed, forming preliminary frequency band screening indicators. Simultaneously, referring to the recommended settings for MT frequency response range in the existing "Technical Regulations for Geophysical Exploration," and the signal-to-noise ratio evaluation experience commonly used in typical domestic and international observation cases, the characteristics of interference background intensity and the distribution of natural field energy spectrum are further combined to determine representative energy-dense frequency band intervals in the current observation area. Finally, an expert group sets upper and lower frequency limits, such as 0.1–10Hz or 0.1–30Hz, based on the on-site observation targets and system sensitivity requirements, to ensure that the selected frequency bands can represent the frequency energy of the observation targets and have reasonable directional discrimination resolution and anti-interference capabilities, thereby scientifically constructing the effective frequency bands required for calculating electric field noise energy density. S35. Utilize Fast Fourier Transform (FFT) technology to analyze the electric field spectrum in each direction, identify the spectral energy within the range of 50Hz ± 1Hz, and calculate its proportion of the total energy, which is used as the main power frequency interference weighting factor W in the current direction. .

[0038] In this embodiment, after identifying the "first stable period", a multi-directional sensing acquisition array is actively constructed. By using spectrum analysis techniques such as Fast Fourier Transform (FFT) and Welch averaging, combined with the electric field noise energy density and power frequency interference weighting factor within a set frequency band, the quantitative identification and fine evaluation of local directional interference are effectively achieved. This ensures that the main observation direction with the least interference is selected in the complex low-resistivity environment of the salt lake area, thereby improving the signal-to-noise ratio and spatial resolution of subsequent magnetotelluric data from the source.

[0039] Example 6 This embodiment is an explanation of embodiment 5. Specifically, step three also includes: S36, The electric field noise energy density N obtained in unit direction and main power frequency interference weighting factor W After dimensionless processing, the directional interference index GRD for each direction is calculated and obtained. The formula is as follows:

[0040] In the formula, w1 and w2 represent the weighting coefficients of the set parameters; The setting method for w1 and w2 is based on statistical analysis of the distribution characteristics of multi-directional electric field noise and power frequency interference in a large amount of magnetotelluric sounding data, combined with the noise energy density in actual observations. Weighting of 50Hz main power frequency interference To investigate the impact of measurement signal-to-noise ratio and data reliability, an empirical weighting method was used to determine its contribution to the directional interference index. Referring to the differences in environmental electromagnetic background, the significance level of power grid interference, and the frequency band response characteristics of the observation equipment in typical measurement areas, and combining the error sensitivity analysis results of the empirical model, the weighting parameter w1 was set to a range of [0.6, 0.8], emphasizing the priority suppression of broadband noise interference. Correspondingly, based on the normalization constraints... To balance the impact of power frequency interference, the weighted index is designed to have both directional resolution and stability sensitivity. This parameter configuration can be fine-tuned in different test areas to adapt to the directional identification accuracy requirements and data quality assurance strategies under specific electromagnetic environments. S37. By traversing all set observation directions and setting a direction interference threshold Qfg, and comparing it with the direction interference index GRD for each direction. Comparative analysis was conducted to select all those that meet the GRD criteria. The direction ≤Qfg is determined, and a set of low-interference directions is established; the directional interference index GRD is selected from the set of low-interference directions. Minimum value The direction is taken as the optimal principal axis direction.

[0041] The method for setting the directional interference threshold Qfg is as follows: Through long-term monitoring and statistical analysis of magnetotelluric sounding data from typical salt lake areas and other high-conductivity background areas, the electric field noise energy density under different directional deployment conditions is systematically summarized. Weighting factor for power frequency interference The joint distribution characteristics; combined with multiple directional interference indices By analyzing the correlation between the actual observation data quality (such as signal-to-noise ratio, invertible frequency band, and apparent resistivity convergence), key threshold values ​​affecting the accuracy of principal direction selection were extracted. Referring to the technical requirements for power frequency suppression capability and electric field interference tolerance in electromagnetic detection standards, and combining on-site deployment experience, instrument dynamic range performance boundaries, and the probability distribution of artificial interference, the following threshold values ​​were determined: When the threshold is ≤0.2, the impact of electromagnetic interference on the observation data is significantly reduced, which can meet the effective response requirements in a low-resistivity environment and has high directional stability and deployment repeatability. The goal of setting the threshold is to establish a strict directional filtering standard to ensure that under the conditions of complex electromagnetic field fluctuations and extremely low background resistivity, the direction with the least interference is selected as the main observation direction. This optimizes the acquisition path, delay control and duration adjustment strategy from the source, providing a high-quality data foundation for subsequent depth sounding inversion.

[0042] In this embodiment, by constructing the directional interference index GRD and combining it with the weighted evaluation mechanism of electric field noise energy density and power frequency interference weight factor, after comprehensive traversal analysis, a set of low-interference directions that meet the directional interference threshold Qfg is accurately screened out. Finally, the main axis direction with the least interference is selected, realizing the optimal deployment path planning in high conductivity background environments such as salt lake areas. This effectively avoids the weakening of electromagnetic observation quality by directional interference, and significantly improves the stability of observation data, signal-to-noise ratio, and reliability of subsequent inversion results.

[0043] Example 7 This embodiment is an explanation of embodiment 6. Specifically, step three also includes: S38. The applicability and interference suppression capability of the optimal principal axis direction are quantitatively evaluated. After dimensionless processing, the direction selection coefficient Gd is calculated as follows:

[0044] S39. By setting a directional screening threshold Qsx, and comparing and analyzing the directional screening coefficient Gd with the directional screening threshold Qsx, the second evaluation result is obtained, including: When the direction selection coefficient Gd ≥ the direction selection threshold Qsx, it means that there is no directional interference in the current observation window, the current direction is locked as the main observation direction, and the delayed acquisition and control stage is entered. When the directional screening coefficient Gd < the directional screening threshold Qsx, it indicates that there is directional interference in the current observation window, triggering the second early warning instruction and generating the second strategy: temporarily not enter the acquisition process; automatically postpone the decision and wait for the next "new stable period" that meets the field strength stability to carry out directional deployment and interference assessment again, until the directional screening coefficient Gd ≥ the directional screening threshold Qsx.

[0045] The method for obtaining the directional filtering threshold Qsx: Through statistical analysis of a large number of actual magnetotelluric sounding observation cases in salt lake areas and high-interference areas, the interference index of different directions is evaluated. The impact on the quality of effective signal acquisition is assessed, and the optimal direction selection coefficient corresponding to the low-interference direction is extracted. The typical distribution range of the data is determined. Based on the observation success rate, data signal-to-noise ratio variation trend, and equipment directional configuration response under multiple scenarios, the availability levels of multiple directions are classified. Simultaneously, referring to existing electromagnetic detection interference avoidance strategies, electromagnetic coil azimuth layout specifications, and experience in joint directional analysis of the geoelectric and geomagnetic fields, a direction screening threshold of Gd=0.8 is set. This value corresponds to a direction interference index no higher than 0.2, indicating that the current direction is at a low interference level under both the electric field background noise energy density and power frequency interference, effectively ensuring good interference suppression capability in the observation main axis direction. The setting of this threshold aims to scientifically screen out high-interference directions, select the optimal layout direction, significantly improve the signal-to-noise ratio and spectral integrity in the subsequent acquisition window, provide a stable and reliable directional basis for adaptive adjustment of observation duration in low-resistivity areas, and ensure the availability and processing accuracy of observation data.

[0046] In this embodiment, by introducing a comparison and analysis mechanism of the directional filtering coefficient Gd and the directional filtering threshold Qsx, a directional interference availability discrimination standard is established. It can determine in real time within the observation window whether the interference suppression capability of the current main axis direction meets the standard. If the condition is not met, the acquisition is automatically delayed and re-evaluated, ensuring that the observation process is started only when the directional interference risk is controllable and the signal-to-noise ratio is sufficiently guaranteed. This significantly improves the directional adaptability, spectral integrity and acquisition success rate of electromagnetic data in low-resistivity complex regions.

[0047] Example 8 This embodiment is an explanation of embodiment 7. Specifically, step four includes: S41. On the locked main observation direction, the electric field component sequence is acquired in real time by using the ground electric field sensor deployed on the main observation direction. ; S42. Extraction using the envelope averaging method The instantaneous envelope of the electric field is calculated, and the average value is calculated within a time window of 10-30 seconds. After dimensionless processing using the root mean square method, the effective electric field strength value is obtained. The formula is as follows:

[0048] In the formula, M represents the number of sampling points. Let represent the instantaneous value of the electric field at time t for the j-th sampling point; income This reflects the equivalent excitation intensity of the natural geoelectric field in the main direction during the current period, i.e., an indicator of whether the geoelectric field is strong enough to excite a identifiable response in underground structures; especially in salt lake areas, the surface brine results in extremely low resistivity, if... If the ground electric field is too low, it will be difficult for the shallow shielding layer to penetrate, and the response of deep targets will be severely weakened; while when... When the level reaches a high level, it indicates that the current natural field has low resistance penetration capability, which is an ideal time to carry out deep MT exploration. S43. By setting a low-resistance penetration threshold Eth, the effective electric field strength value A comparative analysis with the low-resistance penetration threshold Eth yielded the following third evaluation results: When the effective electric field strength value When the value is ≥ the low-resistivity penetration threshold Eth, it indicates that the observation conditions meet the penetration capability requirements, and the device has the capability to effectively electromagnetically excite shallow low-resistivity structures. It will automatically enter the delayed observation stage and start the final acquisition duration monitoring mechanism. When the effective electric field strength value When the value is less than the low-resistivity penetration threshold Eth, it indicates that the observation conditions do not meet the penetration capability requirements and the ability to effectively electromagnetically excite shallow low-resistivity structures is not available. This triggers the third early warning instruction and generates the third strategy: do not activate the delayed observation mechanism, only maintain the basic observation duration for routine data acquisition, and mark the current time period as a non-enhanced excitation period, waiting for the natural field strength to increase in subsequent time windows before re-evaluating the effectiveness.

[0049] The method for setting the low-resistivity penetration threshold Eth is as follows: Based on statistical analysis of a large amount of geoelectric field observation data in saline lake areas and similar low-resistivity environments, the effectiveness of penetration into shallow low-resistivity structures and deep response signals under different natural electric field strengths is extracted. Combined with geophysical exploration technical specifications and electromagnetic sounding equipment performance parameters, a reasonable critical value for electric field strength is determined. Referring to relevant electromagnetic detection standards, low-resistivity zone observation experience, and actual penetration effect evaluations, these standards typically define the minimum threshold electric field strength required to ensure effective excitation of underground structure responses. This threshold is used to accurately determine the excitation capability during the observation period, ensuring that the geoelectric field can penetrate shallow shielding layers, thereby improving the recognition rate and data quality of deep target responses.

[0050] In this embodiment, by introducing a comparison mechanism between the effective electric field strength value and the low-resistivity penetration threshold Eth, a dynamic evaluation standard for the penetration capability of the geoelectric field is established. This standard can automatically determine whether the current natural field has the ability to penetrate the extremely low-resistivity shielding layer on the surface of the salt lake area before electromagnetic observation, thereby accurately identifying the best time period for deep exploration. This significantly improves the effective excitation rate and depth resolution of the observation data in a low-resistivity environment, ensuring that the acquisition results have higher structural response identification value and inversion reliability.

[0051] Example 9 This embodiment is an explanation of embodiment 8. Specifically, step five includes: S51, By combining the overall electromagnetic field stability index Gt, the direction selection coefficient Gd, and the effective electric field strength value After dimensionless processing, an observation weighting factor is constructed. The formula is as follows:

[0052] In the formula, Ce represents the traction index; ; In the formula, Eth represents the low-resistance penetration threshold; S52, By observing the weighting factors The basic observation time T0 is extended and adjusted, and after dimensionless processing, the final observation time Tfinal is calculated using the following formula:

[0053] In this embodiment, by constructing an observation weighting factor that integrates the overall electromagnetic field stability index Gt, the directional screening coefficient Gd, and the effective electric field strength value, a dynamic extension adjustment mechanism for the basic observation time T0 is realized. This mechanism can automatically optimize the final observation time Tfinal based on the stability of the current natural electromagnetic field, the level of directional interference, and the excitation capability, thereby effectively extending the high-quality data acquisition cycle. While ensuring equipment efficiency, it significantly improves the data signal-to-noise ratio and spectral integrity, making it particularly suitable for high-precision electromagnetic detection operations in low-resistivity, high-interference backgrounds such as salt lake areas.

[0054] Example 10 For an adaptive control system of magnetotelluric sounding duration in low-resistivity areas of salt lakes, please refer to [link / reference needed]. Figure 2 ,include: The electromagnetic field basic acquisition module is used in the observation preparation stage before the start of magnetotelluric sounding. It selects electric field measurement points within the survey line area of ​​the salt lake area and acquires the east-west electric field time series Ex(t) and the north-south electric field time series Ey(t) of the target measurement points in real time. It also deploys a triaxial induction coil magnetometer to acquire the high-resolution geomagnetic field north-south component series Hx(t), east-west component series Hy(t), and vertical component series Hz(t) in real time. Finally, it installs a synchronous electromagnetic field observation device to record the initial stable values ​​of the local reference electric field E0 and magnetic field H0. The electromagnetic field stability monitoring module is used to calculate and obtain the electric field change rate index SE and the magnetic field change rate index SH, and further calculate and obtain the overall electromagnetic field stability index Gt. These are compared and analyzed with the change rate threshold Qbh and the overall electromagnetic field stability threshold Qdw to determine whether the current electromagnetic field is in a stable state and to establish the first stable period. If it is in a stable state, it enters the observation pre-activation state and starts the interference source analysis mechanism. If it is unstable, a strategy is given. The directional interference identification module is used to acquire the original time series signal E by selecting electric field measuring points along the survey line in the salt lake area and deploying a geomagnetic induction coil array after identifying the first stable period. (t), and calculate the power spectral density. Electric field noise energy density N in unit direction Further calculations were performed to obtain the directional interference index (GRD) for each direction. The values ​​are evaluated against the directional interference threshold Qfg, and a set of low-interference directions is established; the minimum value is selected. The direction selection coefficient Gd is calculated and compared with the direction selection threshold Qsx to lock the current direction as the main observation direction. The effective electric field penetration monitoring module is used to acquire electric field component sequences in real time along the locked main observation direction using ground electric field sensors deployed along that direction. Calculate and obtain the effective electric field strength value The data is compared with the low-resistivity penetration threshold Eth to determine whether the observation conditions meet the penetration capability requirements. If they do, the final acquisition duration monitoring mechanism is activated; otherwise, a strategy is provided. The final observation time correction module is used to combine the overall electromagnetic field stability index Gt, the direction selection coefficient Gd, and the effective electric field strength value. Construct observation weighting factors The final observation time Tfinal is then calculated.

[0055] In this embodiment, by constructing a complete module system integrating basic electromagnetic field acquisition, stability monitoring, directional interference identification, penetration capability determination, and observation duration correction, multi-dimensional dynamic analysis and intelligent decision-making are achieved in the preparation stage of magnetotelluric sounding observation under the complex low-resistivity background of the salt lake area. Under the premise of ensuring stable field strength, minimal directional interference, and qualified penetration capability, the main observation direction and final observation time are automatically optimized, effectively improving the integrity and reliability of electromagnetic detection data and significantly enhancing the acquisition efficiency of deep structure response in low-resistivity areas.

[0056] The threshold is set to facilitate comparison. The size of the threshold depends on the amount of sample data and the number of bases set by those skilled in the art for each set of sample data; as long as it does not affect the ratio between the parameter and the quantized value, it is acceptable.

[0057] The above formulas are all derived from software simulation using a large amount of data, and are selected to be close to the actual values. The coefficients in the formulas are set by those skilled in the art based on the actual situation. The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or changes made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. An adaptive adjustment method for magnetotelluric sounding observation duration in low-resistivity salt lake areas, characterized in that, Includes the following steps: Step 1: In the observation preparation stage before the start of the magnetotelluric sounding observation, select electric field measuring points within the survey line area of ​​the salt lake area, and collect the east-west electric field time series Ex(t) and the north-south electric field time series Ey(t) of the target measuring points in real time; deploy a triaxial induction coil magnetometer to collect the high-resolution geomagnetic field north-south component series Hx(t), east-west component series Hy(t), and vertical component series Hz(t) in real time; install a synchronous electromagnetic field observation device to record the initial stable values ​​of the local reference electric field E0 and magnetic field H0; Step 2: Calculate and obtain the electric field change rate index SE and the magnetic field change rate index SH, and further calculate and obtain the overall electromagnetic field stability index Gt. Compare and analyze these with the change rate threshold Qbh and the overall electromagnetic field stability threshold Qdw to determine whether the current electromagnetic field is in a stable state and establish the first stable period. If it is in a stable state, enter the observation pre-activation state and start the interference source analysis mechanism; if it is unstable, provide a strategy. Step 3: After identifying the first stable period, select electric field measuring points along the survey line in the salt lake area, deploy a geomagnetic induction coil array, and acquire the original time series signal E. (t), and calculate the power spectral density. Electric field noise energy density N in unit direction Further calculations were performed to obtain the directional interference index (GRD) for each direction. The values ​​are evaluated against the directional interference threshold Qfg, and a set of low-interference directions is established; the minimum value is selected. The direction selection coefficient Gd is calculated and compared with the direction selection threshold Qsx to lock the current direction as the main observation direction. Step 4: Along the locked main observation direction, collect the electric field component sequence in real time using the ground electric field sensors deployed along the main observation direction. Calculate and obtain the effective electric field strength value The data is compared with the low-resistivity penetration threshold Eth to determine whether the observation conditions meet the penetration capability requirements. If they do, the final acquisition duration monitoring mechanism is activated; otherwise, a strategy is provided. Step 5: By combining the overall electromagnetic field stability index Gt, the direction selection coefficient Gd, and the effective electric field strength value Construct observation weighting factors The final observation time Tfinal is then calculated.

2. The adaptive adjustment method for magnetotelluric sounding duration in low-resistivity salt lake areas according to claim 1, characterized in that, Step one includes: S11. Before the commencement of magnetotelluric sounding observation, electric field measuring points were selected within the survey line area of ​​the salt lake region. Two pairs of non-polarized electrodes were symmetrically buried along the east-west and north-south directions, respectively. The electrode spacing was set at 50 meters and the burial depth at 20 centimeters. A horizontal dipole was constructed and connected to a low-noise electric field amplifier and a high-precision data acquisition device. The real-time acquisition of the horizontal electric field time series in two directions of the ground electric field included: the east-west electric field time series Ex(t) and the north-south electric field time series Ey(t). S12. At a distance of 15 meters from the electric field measurement, a triaxial induction coil magnetometer is laid out along the east-west, north-south and vertical directions respectively, and high-resolution geomagnetic field north-south component sequence Hx(t), east-west component sequence Hy(t) and vertical component sequence Hz(t) are collected in real time. S13. Set up a continuous reference measuring point within 3 kilometers of the target observation point, install a synchronous electromagnetic field observation device, and record the initial stable values ​​of the local reference electric field E0 and magnetic field H0.

3. The adaptive adjustment method for magnetotelluric sounding duration in low-resistivity salt lake areas according to claim 2, characterized in that, Step two includes: S21. Obtain the rate of change of the electric field at the target observation point by using the moving average difference smoothing differentiation technique on the time series of the horizontal electric field in two directions of the ground electric field Ex(t) and Ey(t). By approximating the derivatives of the high-resolution geomagnetic field north-south component sequence Hx(t), east-west component sequence Hy(t), and vertical component sequence Hz(t) at each time point using numerical differentiation algorithms such as central difference, the rate of change of the geomagnetic field at the target observation point is obtained. ; S22. Based on the rate of change of the electric field at the target observation point and the rate of change of the geomagnetic field at the target observation point By combining the initial stable values ​​of the reference electric field E0 and the initial stable value of the magnetic field H0, and after dimensionless processing, the electric field rate of change exponent SE and the magnetic field rate of change exponent SH are calculated and obtained respectively. S23. By combining the electric field rate of change index SE and the magnetic field rate of change index SH, and after dimensionless processing, the overall electromagnetic field stability index Gt is calculated and obtained.

4. The adaptive adjustment method for magnetotelluric sounding duration in low-resistivity salt lake areas according to claim 3, characterized in that, Step two also includes: S24. By setting a change rate threshold Qbh and an overall electromagnetic field stability threshold Qdw, and comparing the electric field change rate index SE and the magnetic field change rate index SH with the change rate threshold Qbh, and comparing the overall electromagnetic field stability index Gt with the overall electromagnetic field stability threshold Qdw, the first evaluation results are obtained, including: When the electric field rate of change exponent SE ≤ the rate of change threshold Qbh, the magnetic field rate of change exponent SH ≤ the rate of change threshold Qbh, and at the same time the electromagnetic field overall stability exponent Gt ≥ the electromagnetic field overall stability threshold Qdw, it indicates that the current electromagnetic field is in a stable state, which is recorded as the "first stable period", and the observation pre-activation state is entered, and the interference source analysis mechanism is started. When either the electric field rate of change index SE or the magnetic field rate of change index SH is greater than the rate of change threshold Qbh, or when the overall electromagnetic field stability index Gt is less than the overall electromagnetic field stability threshold Qdw, it indicates that the current electromagnetic field is in an unstable state, triggering the first warning command and generating the first strategy: automatically execute the observation suspension command, enter the waiting state, and reassess the next time window once every 5 minutes at a set time interval.

5. The adaptive adjustment method for magnetotelluric sounding duration in low-resistivity salt lake areas according to claim 4, characterized in that, Step three includes: S31. After identifying the "first stable period", select electric field measurement points on the survey line in the salt lake area, and with the center as the base point, rotate the geomagnetic induction coil array every 15° according to the polar coordinate angle to complete the induction measurement array layout in 12 directions. S32. During the first stable period, a synchronous acquisition device is used to record the electric field noise data corresponding to each direction, and the original time series signal E is obtained. (t), and then perform segmented windowing processing, and then use Fast Fourier Transform (FFT) on each segment of the signal to extract the energy distribution on each frequency component and obtain the spectrum of the signal. S33. The Welch averaging method is used to perform square averaging on the FFT results of each segment. After dimensionless processing, the power spectral density is constructed. ; S34, via power spectral density A frequency band is defined, and the power spectral density within the band is integrated. After dimensionless processing, the electric field noise energy density N per unit direction is calculated. S35. Utilize Fast Fourier Transform (FFT) technology to analyze the electric field spectrum in each direction, identify the spectral energy within the range of 50Hz ± 1Hz, and calculate its proportion of the total energy, which is used as the main power frequency interference weighting factor W in the current direction. .

6. The adaptive adjustment method for magnetotelluric sounding duration in low-resistivity salt lake areas according to claim 5, characterized in that, Step three also includes: S36, The electric field noise energy density N obtained in unit direction and main power frequency interference weighting factor W After dimensionless processing, the directional interference index GRD for each direction is calculated and obtained. ; S37. By traversing all set observation directions and setting a direction interference threshold Qfg, and comparing it with the direction interference index GRD for each direction. Comparative analysis was conducted to select all those that meet the GRD criteria. The direction ≤Qfg is determined, and a set of low-interference directions is established; the directional interference index GRD is selected from the set of low-interference directions. Minimum value The direction is taken as the optimal principal axis direction.

7. The adaptive adjustment method for magnetotelluric sounding duration in low-resistivity salt lake areas according to claim 6, characterized in that, Step three also includes: S38. Quantitative evaluation is performed using the optimal principal axis direction. After dimensionless processing, the direction selection coefficient Gd is calculated and obtained. S39. By setting a directional screening threshold Qsx, and comparing and analyzing the directional screening coefficient Gd with the directional screening threshold Qsx, the second evaluation result is obtained, including: When the direction selection coefficient Gd ≥ the direction selection threshold Qsx, it means that there is no directional interference in the current observation window, the current direction is locked as the main observation direction, and the delayed acquisition and control stage is entered. When the directional screening coefficient Gd < the directional screening threshold Qsx, it indicates that there is directional interference in the current observation window, triggering the second early warning instruction and generating the second strategy: temporarily not enter the acquisition process; automatically postpone the decision and wait for the next "new stable period" that meets the field strength stability to carry out directional deployment and interference assessment again, until the directional screening coefficient Gd ≥ the directional screening threshold Qsx.

8. The adaptive adjustment method for magnetotelluric sounding duration in low-resistivity salt lake areas according to claim 7, characterized in that, Step four includes: S41. On the locked main observation direction, the electric field component sequence is acquired in real time by using the ground electric field sensor deployed on the main observation direction. ; S42. Extraction using the envelope averaging method The instantaneous envelope of the electric field is calculated, and the average value is calculated within a time window of 10-30 seconds. After dimensionless processing using the root mean square method, the effective electric field strength value is obtained. ; S43. By setting a low-resistance penetration threshold Eth, the effective electric field strength value A comparative analysis with the low-resistance penetration threshold Eth yielded the following third evaluation results: When the effective electric field strength value When the value is ≥ the low-resistivity penetration threshold Eth, it indicates that the observation conditions meet the penetration capability requirements, and the device has the capability to effectively electromagnetically excite shallow low-resistivity structures. It will automatically enter the delayed observation stage and start the final acquisition duration monitoring mechanism. When the effective electric field strength value When the value is less than the low-resistivity penetration threshold Eth, it indicates that the observation conditions do not meet the penetration capability requirements and the ability to effectively electromagnetically excite shallow low-resistivity structures is not available. This triggers the third early warning instruction and generates the third strategy: do not activate the delayed observation mechanism, only maintain the basic observation duration for routine data acquisition, and mark the current time period as a non-enhanced excitation period, waiting for the natural field strength to increase in subsequent time windows before re-evaluating the effectiveness.

9. The adaptive adjustment method for magnetotelluric sounding duration in low-resistivity salt lake areas according to claim 8, characterized in that, Step five includes: S51, By combining the overall electromagnetic field stability index Gt, the direction selection coefficient Gd, and the effective electric field strength value After dimensionless processing, an observation weighting factor is constructed. ; S52, By observing the weighting factors The basic observation time T0 is extended and adjusted, and after dimensionless processing, the final observation time Tfinal is calculated.

10. An adaptive control system for magnetotelluric sounding observation duration in low-resistivity areas of salt lakes, comprising the adaptive control method for magnetotelluric sounding observation duration in low-resistivity areas of salt lakes according to claims 1-9, characterized in that... include: The electromagnetic field basic acquisition module is used in the observation preparation stage before the start of magnetotelluric sounding. It selects electric field measurement points within the survey line area of ​​the salt lake area and acquires the east-west electric field time series Ex(t) and the north-south electric field time series Ey(t) of the target measurement points in real time. It also deploys a triaxial induction coil magnetometer to acquire the high-resolution geomagnetic field north-south component series Hx(t), east-west component series Hy(t), and vertical component series Hz(t) in real time. Finally, it installs a synchronous electromagnetic field observation device to record the initial stable values ​​of the local reference electric field E0 and magnetic field H0. The electromagnetic field stability monitoring module is used to calculate and obtain the electric field change rate index SE and the magnetic field change rate index SH, and further calculate and obtain the overall electromagnetic field stability index Gt. These are compared and analyzed with the change rate threshold Qbh and the overall electromagnetic field stability threshold Qdw to determine whether the current electromagnetic field is in a stable state and to establish the first stable period. If it is in a stable state, it enters the observation pre-activation state and starts the interference source analysis mechanism. If it is unstable, a strategy is given. The directional interference identification module is used to acquire the original time series signal E by selecting electric field measuring points along the survey line in the salt lake area and deploying a geomagnetic induction coil array after identifying the first stable period. (t), and calculate the power spectral density. Electric field noise energy density N in unit direction Further calculations were performed to obtain the directional interference index (GRD) for each direction. The values ​​are evaluated against the directional interference threshold Qfg, and a set of low-interference directions is established; the minimum value is selected. The direction selection coefficient Gd is calculated and compared with the direction selection threshold Qsx to lock the current direction as the main observation direction. The effective electric field penetration monitoring module is used to acquire electric field component sequences in real time along the locked main observation direction using ground electric field sensors deployed along that direction. Calculate and obtain the effective electric field strength value The data is compared with the low-resistivity penetration threshold Eth to determine whether the observation conditions meet the penetration capability requirements. If they do, the final acquisition duration monitoring mechanism is activated; otherwise, a strategy is provided. The final observation time correction module is used to combine the overall electromagnetic field stability index Gt, the direction selection coefficient Gd, and the effective electric field strength value. Construct observation weighting factors The final observation time Tfinal is then calculated.

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