Method and system for identification and suppression of electromagnetic interference in electromagnetic frequency sounding

Abstract

The application discloses a kind of electromagnetic interference identification and suppression method and system in electromagnetic frequency depth finding, comprising: repeated data acquisition is carried out to each frequency in sampling frequency band, and first data set is obtained, and first electric field-frequency scatter diagram is further obtained;Identify whether there is a node in first electric field-frequency scatter diagram The node is removed, if yes, find the node removed from first electric field-frequency scatter diagram;Get the electromagnetic frequency current normalized electric field of the node removed and the node not removed, and obtain the degree of electromagnetic interference of the node removed according to the electromagnetic frequency current normalized electric field;Determine whether the degree of electromagnetic interference exceeds threshold value, if yes, reacquire data through interference suppression, obtain second data set, further obtain second electric field-frequency scatter diagram, observe whether there is a node removed in second electric field-frequency scatter diagram, if no, it is considered that the suppression of electromagnetic interference is completed.The application achieves the purpose of effectively suppressing electromagnetic interference and obtaining effective acquisition data.

Description

Technical Field

[0001] This invention relates to the field of geological exploration technology, specifically to a method and system for identifying and suppressing electromagnetic interference in electromagnetic frequency sounding. Background Technology

[0002] The main factor affecting the acquisition of electromagnetic exploration data and the quality of exploration results is electromagnetic interference, among which electromagnetic interference caused by high-voltage lines and harmonics is the most serious. In order to reduce electromagnetic interference, corresponding suppression technologies have been proposed from aspects such as instrument design and manufacturing, field data acquisition, and indoor data processing.

[0003] Existing methods for suppressing electromagnetic interference (EMI) fall into three categories: First, suppressing EMI through instrument design, specifically by designing notch filters for the interference frequency. Second, enhancing the useful signal and improving the signal-to-noise ratio during field operations by increasing the transmit current, widening the field source A / B pole distance, and reducing the transmit / receive distance. Third, suppressing EMI through post-processing of multiple data acquisitions. Without considering instrument design, and focusing solely on data acquisition and processing, existing technologies suffer from the following technical problems:

[0004] (1) The existing method of “enhancing useful signals and improving signal-to-noise ratio by increasing the transmission current, increasing the field source AB pole distance, and reducing the transmission and receiving distance” is still not ideal in practical applications in terms of reducing electromagnetic fields, which results in the acquired data still being subject to significant interference.

[0005] (2) Post-processing of multiple data acquisitions mainly involves data filtering. Common geophysical methods use the average of multiple acquisitions as the final data. This approach assumes the interference is random noise, which contradicts the characteristics of strong electromagnetic interference from high-voltage lines and optical fibers. Averaging multiple data sets fails to suppress interference. Some have proposed using information entropy for rational filtering of multiple electric field measurements, but this is essentially median filtering, which, like averaging, fails to suppress electromagnetic interference caused by high-voltage lines and optical fibers. Summary of the Invention

[0006] To overcome the shortcomings of the prior art, the present invention provides a method and system for identifying and suppressing electromagnetic interference in electromagnetic frequency sounding, which solves the technical problem that the existing methods are not effective in suppressing electromagnetic interference, thereby achieving the purpose of effectively suppressing electromagnetic interference and obtaining effective data acquisition.

[0007] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0008] A method for identifying and suppressing electromagnetic interference in electromagnetic frequency sounding includes the following steps:

[0009] Repeated data collection is performed for each frequency in the sampling frequency band to obtain the first dataset, and the first electric field-frequency scatter plot is obtained based on the first dataset.

[0010] Identify whether there are any detached nodes in the first electric field-frequency scatter plot. If so, find the detached nodes in the first electric field-frequency scatter plot.

[0011] Obtain the normalized electric field of the electromagnetic frequency current for the disconnected and non-disconnected nodes, and obtain the degree of electromagnetic interference of the disconnected node based on the normalized electric field of the electromagnetic frequency current.

[0012] Determine whether the degree of electromagnetic interference exceeds a threshold. If so, reacquire data through interference suppression to obtain a second dataset. Obtain a second electric field-frequency scatter plot based on the second dataset. Observe whether there are any missing nodes in the second electric field-frequency scatter plot. If not, it is considered that the electromagnetic interference suppression has been completed.

[0013] In a preferred embodiment of the present invention, when identifying whether the second electric field-frequency scatter plot has de-nodes, the method further includes:

[0014] If so, it is further determined whether the number of detached nodes in the second electric field-frequency scatter plot exceeds the threshold. If not, it is considered that the suppression of electromagnetic interference has been completed. If so, data is reacquired through interference suppression until the suppression of electromagnetic interference is completed.

[0015] In a preferred embodiment of the present invention, when repeatedly collecting data for each frequency, the following steps are included:

[0016] Preset the first number of samples, the second number of samples, the first frequency band value, and the second frequency band value;

[0017] Determine whether each frequency in the sampling frequency band is at the value of the first frequency band or the value of the second frequency band;

[0018] If the frequency is within the first frequency band, then the frequency is repeatedly sampled according to the first number of samples.

[0019] If the frequency is in the second frequency band, then the frequency is repeatedly sampled according to the second sampling number.

[0020] In a preferred embodiment of the present invention, when obtaining the degree of electromagnetic interference experienced by the disconnected node based on the normalized electric field of the electromagnetic frequency current, the method includes:

[0021] Obtain the root mean square relative difference of the electromagnetic frequency current normalized electric field for each of the said de-nodes, and obtain the total root mean square relative difference of the de-nodes based on the root mean square difference of all the said de-nodes.

[0022] Obtain the root mean square relative difference of the electromagnetic frequency current normalized electric field for each of the non-detached nodes, and obtain the total root mean square relative difference of the non-detached nodes based on the root mean square difference of all the non-detached nodes.

[0023] Obtain the difference between the total root mean square relative difference of the nodes that have been removed and the total root mean square relative difference of the nodes that have not been removed;

[0024] The difference represents the degree of electromagnetic interference experienced by the disconnected node.

[0025] In a preferred embodiment of the present invention, the process of obtaining the root-mean-square relative difference between the normalized electric fields of the electromagnetic frequency currents of the disconnected and non-disconnected nodes includes:

[0026] Based on the normalized electric field of the current collected from the detached node and the non-detached node, and the mean value of the normalized electric field of the current measured from each detached node and the non-detached node, the root mean square relative difference of the electromagnetic frequency current normalized electric field between the detached node and the non-detached node is obtained, as shown in Formula 1:

[0027]

[0028] In the formula, E i,j Let i be the normalized electric field of the current obtained from the j-th sampling at frequency i. Let be the mean of the normalized electric field of the measured current at frequency i.

[0029] In a preferred embodiment of the present invention, when reacquiring data through interference suppression, the following is included:

[0030] Based on the acquisition area of ​​the first dataset, a region closer to the field source is determined to carry out electric field data acquisition, thereby improving the signal-to-noise ratio of the acquired data and suppressing electromagnetic interference.

[0031] In a preferred embodiment of the present invention, when reacquiring data through interference suppression, the following is included:

[0032] Set the initial electric field value at the frequency point, and obtain the filter coefficient of each measurement data based on the difference between each measurement data and the initial electric field value;

[0033] The initial electric field value is iteratively updated based on the filter coefficients of each measurement data to obtain data that is closer to the true electric field value.

[0034] In a preferred embodiment of the present invention, when reacquiring data through interference suppression, the following is included:

[0035] By incorporating data from surrounding frequency points in the first dataset, interference estimation filtering is performed, as shown in Formula 2:

[0036]

[0037] In the formula, n is the number of frequency points involved in the filtering calculation, m(i) is the number of times the electric field is repeatedly measured at each frequency point, and w i,j E represents the filter coefficients. i,j Let be the electric field measured at the i-th frequency point for the j-th time.

[0038] In a preferred embodiment of the present invention, when reacquiring data through interference suppression, the following is included:

[0039] Identify the interference source causing electromagnetic interference to the first dataset, obtain the main direction of the interference source, and repeatedly collect data for each frequency perpendicular to the main direction of the interference source to suppress the electromagnetic interference from the interference source.

[0040] A system for identifying and suppressing electromagnetic interference in electromagnetic frequency sounding, comprising:

[0041] Acquisition unit: used to repeatedly acquire data for each frequency in the sampling frequency band to obtain a first dataset, and to obtain a first electric field-frequency scatter plot based on the first dataset;

[0042] Identification unit: used to identify whether there are any detached nodes in the first electric field-frequency scatter plot; if so, to find the detached nodes in the first electric field-frequency scatter plot.

[0043] Interference level acquisition unit: used to acquire the normalized electric field of electromagnetic frequency current for the disconnected node and the non-disconnected node, and to obtain the degree of electromagnetic interference of the disconnected node based on the normalized electric field of electromagnetic frequency current.

[0044] Interference suppression unit: used to determine whether the degree of electromagnetic interference exceeds the threshold. If so, the data is reacquired through interference suppression to obtain a second dataset. A second electric field-frequency scatter plot is obtained based on the second dataset. The second electric field-frequency scatter plot is observed to see if there are any missing nodes. If not, the electromagnetic interference suppression is considered to be complete.

[0045] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0046] (1) The electromagnetic interference identification method proposed in this invention can help technicians more effectively determine whether the collected data has been interfered with, thereby further determining whether the data is valid data, and obtaining the data again through the corresponding interference suppression method to ensure the validity of the data;

[0047] (2) This invention improves the signal-to-noise ratio and suppresses electromagnetic interference more effectively by collecting electric field data in a region closer to the field source. Compared with the traditional method of increasing the emission current, it can obtain more effective data.

[0048] (3) This invention proposes an interference estimation filtering technique, which, compared with the traditional technique of suppressing electromagnetic interference by averaging multiple repeated measurements, can obtain data that is closer to the true electric field value.

[0049] (4) The present invention proposes to repeatedly collect data in the main direction perpendicular to the interference source, so that the collected data can withstand strong electromagnetic interference.

[0050] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0051] Figure 1 - This is a diagram of the electric field data of severe electromagnetic interference in a certain area of ​​Shanxi Province according to an embodiment of the present invention;

[0052] Figure 2 - This is a diagram of the electric field data of slight electromagnetic interference in a certain area of ​​Shanxi Province according to an embodiment of the present invention;

[0053] Figure 3 - This is a diagram showing the relationship between the location of measuring point 1 in a construction area in Anhui Province and the high-voltage line, according to an embodiment of the present invention.

[0054] Figure 4 - This is a measured electric field diagram of the relationship between a construction site 1 in Anhui Province and a high-voltage line at different locations, according to an embodiment of the present invention;

[0055] Figure 5 - This is a measured electric field diagram of the relationship between a construction site 2 in Anhui Province and a high-voltage line at different locations according to an embodiment of the present invention;

[0056] Figure 6 This is an image showing the interference suppression effect of severe electromagnetic interference electric field data in a certain area of ​​Shanxi Province according to an embodiment of the present invention;

[0057] Figure 7 This is an image showing the interference suppression effect of slight electromagnetic interference electric field data in a certain area of ​​Shanxi Province according to an embodiment of the present invention;

[0058] Figure 8 This is an interference suppression effect diagram of a severely electromagnetically interfered measurement point 2 in a construction area in Anhui Province, according to an embodiment of the present invention.

[0059] Figure 9 These are electric field data diagrams of the MN electrode and the high-voltage line at angles of 19 degrees and 71 degrees, respectively, according to embodiments of the present invention.

[0060] Figure 10 This is a flowchart illustrating the steps of the method for identifying and suppressing electromagnetic interference in electromagnetic frequency sounding according to an embodiment of the present invention. Detailed Implementation

[0061] The method for identifying and suppressing electromagnetic interference in electromagnetic frequency sounding provided by this invention, such as... Figure 10 As shown, it includes the following steps:

[0062] Step S1: Repeatedly collect data for each frequency in the sampling frequency band to obtain the first dataset, and obtain the first electric field-frequency scatter plot based on the first dataset;

[0063] Step S2: Identify whether there are any detached nodes in the first electric field-frequency scatter plot. If so, find the detached nodes in the first electric field-frequency scatter plot.

[0064] Step S3: Obtain the normalized electric field of electromagnetic frequency current for both disconnected and non-disconnected nodes, and obtain the degree of electromagnetic interference experienced by disconnected nodes based on the normalized electric field of electromagnetic frequency current.

[0065] Step S4: Determine whether the degree of electromagnetic interference exceeds the threshold. If so, reacquire the data through interference suppression to obtain the second dataset. Obtain the second electric field-frequency scatter plot based on the second dataset. Observe whether there are any missing nodes in the second electric field-frequency scatter plot. If not, it is considered that the electromagnetic interference suppression is completed.

[0066] In step S4 above, when identifying whether there are de-nodes in the second electric field-frequency scatter plot, the following is also included:

[0067] If so, then it is further determined whether the number of disconnected nodes in the second electric field-frequency scatter plot exceeds the threshold. If not, it is considered that the electromagnetic interference suppression has been completed. If so, the data is reacquired through interference suppression until the electromagnetic interference suppression is completed.

[0068] In step S1 above, when repeatedly collecting data for each frequency, the following is included:

[0069] Preset the first number of samples, the second number of samples, the first frequency band value, and the second frequency band value;

[0070] Determine whether each frequency in the sampling frequency band falls within the first frequency band value or the second frequency band value;

[0071] If it is in the first frequency band, then the frequency data is repeatedly collected based on the first number of samples;

[0072] If it is in the second frequency band, then the frequency will be repeatedly sampled according to the second sampling number.

[0073] In step S3 above, when obtaining the degree of electromagnetic interference experienced by the disconnected node based on the normalized electric field of the electromagnetic frequency current, the following steps are included:

[0074] Obtain the root mean square relative difference of the electromagnetic frequency current normalized electric field for each disconnected node, and obtain the total root mean square relative difference of the disconnected nodes based on the root mean square difference of all disconnected nodes.

[0075] Obtain the root mean square relative difference of the electromagnetic frequency current normalized electric field for each non-detached node, and obtain the total root mean square relative difference of the non-detached nodes based on the root mean square difference of all non-detached nodes.

[0076] Obtain the difference between the total root mean square relative difference of nodes that have been removed from the node and the total root mean square relative difference of nodes that have not been removed from the node.

[0077] The difference represents the degree of electromagnetic interference experienced by the disconnected node.

[0078] Furthermore, when obtaining the root-mean-square relative difference between the normalized electric field of the electromagnetic frequency current for both detached and non-detached nodes, the following steps are included:

[0079] Based on the normalized electric field of the current collected from both the detached and non-detached nodes, and the average value of the normalized electric field of the current measured from each detached and non-detached node, the root mean square relative difference of the electromagnetic frequency current normalized electric field between the detached and non-detached nodes is obtained, as shown in Formula 1:

[0080]

[0081] In the formula, E i,j Let i be the normalized electric field of the current obtained from the j-th sampling at frequency i. Let be the mean of the normalized electric field of the measured current at frequency i.

[0082] In step S4 above, when reacquiring data through interference suppression, the following steps are included:

[0083] Based on the acquisition area of ​​the first dataset, a region closer to the field source is determined to carry out electric field data acquisition, thereby improving the signal-to-noise ratio of the acquired data and suppressing electromagnetic interference.

[0084] In step S4 above, when reacquiring data through interference suppression, the following steps are included:

[0085] Set the initial electric field value at the frequency point, and obtain the filter coefficient of each measurement data based on the difference between each measurement data and the initial electric field value;

[0086] The initial electric field value is updated iteratively based on the filter coefficients of each measurement data to obtain data that is closer to the true electric field value.

[0087] In step S4 above, when reacquiring data through interference suppression, the following steps are included:

[0088] By incorporating data from surrounding frequency points in the first dataset, interference estimation filtering is performed, specifically as follows:

[0089] As shown in Equation 2:

[0090]

[0091] In the formula, n is the number of frequency points involved in the filtering calculation, m(i) is the number of times the electric field is repeatedly measured at each frequency point, and w i,j E represents the filter coefficients. i,j Let be the electric field measured at the i-th frequency point for the j-th time.

[0092] In step S4 above, when reacquiring data through interference suppression, the following steps are included:

[0093] Identify the interference source causing electromagnetic interference to the first dataset, obtain the main direction of the interference source, and repeatedly collect data for each frequency perpendicular to the main direction of the interference source to suppress the electromagnetic interference from the interference source.

[0094] Specifically, the electromagnetic field generated by an electric dipole on the Earth's surface increases with the increase of the electric dipole moment Idx and decreases with the increase of the distance between the transmitter and receiver (AB-MN). Taking the electric field as an example, we have... In other words, increasing the transmitting current (increasing the field source AB pole distance in the background technology) is not as effective as reducing the distance between the transmitter and receiver. Therefore, this invention conducts electric field data acquisition in a region as close as possible to the field source, thereby more effectively improving the signal-to-noise ratio and suppressing electromagnetic interference.

[0095] In response to existing methods of "post-processing of multiple data acquisitions" in the background art, this invention proposes an interference estimation filtering technique based on two fundamental assumptions:

[0096] First, the signal-to-noise ratio of electric field data measured repeatedly at each frequency point is different, but there is always a true electric field value. Therefore, by setting an initial electric field value for each frequency point, the filter coefficient of each measurement data is calculated based on the difference between each measurement data and the initial electric field value, and the initial electric field value is iteratively updated to obtain data that is relatively closer to the true electric field value.

[0097] Second, the electric field value at each frequency point is continuous and correlated with the electric field values ​​at other nearby frequencies. By adding data information from surrounding frequencies during the filtering process, data that is closer to the true electric field value can be obtained, as shown in Formula 2 above.

[0098] The electromagnetic interference identification and suppression system in electromagnetic frequency sounding provided by this invention includes: a data acquisition unit, an identification unit, an interference level acquisition unit, and an interference suppression unit. The data acquisition unit repeatedly acquires data for each frequency in the sampling frequency band to obtain a first dataset, and obtains a first electric field-frequency scatter plot based on the first dataset. The identification unit identifies whether there are any detached nodes in the first electric field-frequency scatter plot; if so, it locates the detached nodes from the first electric field-frequency scatter plot. The interference level acquisition unit acquires the normalized electric field of the electromagnetic frequency current for detached and non-detached nodes, and obtains the degree of electromagnetic interference experienced by the detached nodes based on the normalized electric field of the electromagnetic frequency current. The interference suppression unit determines whether the degree of electromagnetic interference exceeds a threshold; if so, it re-acquires data through interference suppression to obtain a second dataset, obtains a second electric field-frequency scatter plot based on the second dataset, and observes whether there are any detached nodes in the second electric field-frequency scatter plot; if not, it considers the electromagnetic interference suppression to be complete.

[0099] The following embodiments are further illustrations of the present invention, but the scope of the present invention is not limited thereto.

[0100] Example 1 (Interference Identification)

[0101] Figure 1 This is a data map of severe electromagnetic interference in a certain area of ​​Shanxi Province. The measurement data covers 56 frequencies from 0.625 to 8192 Hz. Data was repeatedly collected at each frequency. Due to the higher signal-to-noise ratio (SNR) in the low-frequency band, fewer repetitions were needed, while the high-frequency band had a lower SNR and more repetitions, up to 30 times. The measurement point is located 20-40 meters away from a high-voltage power line and a natural gas pipeline (containing a fiber optic leak detection sensor). Figure 1 It can be seen that data above 450Hz are basically affected by electromagnetic interference (among which 448, 1280, 3072, 3584, 6144, and 7160 are most severely affected by interference), and data at two frequencies around 50Hz are severely affected by electromagnetic interference.

[0102] Figure 2 This is a data map of electric field from a location in Shanxi Province experiencing slight electromagnetic interference. The map shows that single-frequency points of 48, 448, 1280, and 2048 Hz are affected by electromagnetic interference. Overall, the frequency electromagnetic sounding electric field data affected by electromagnetic interference show significantly higher values ​​than undisturbed data. Data severely affected by interference show continuously higher values ​​at consecutive frequencies than normal. Figure 2 There are obvious detached nodes that can be seen in the image.

[0103] To further verify the above characteristics, electromagnetic frequency depth sounding data of work area 1 in a certain area of ​​Anhui were analyzed. Figure 3 This is a diagram showing the location relationship between measuring point 1 and the high-voltage line in a construction area in Anhui Province. Figure 3It can be seen that the MN electrode at point 4510 on line 4820 is nearly parallel to the high voltage line, the MN electrode at point 4650 on line 4820 is located near the intersection of the high voltage line, and the MN electrodes at points 4550 and 4690 on line 5380 are nearly perpendicular to the high voltage line.

[0104] Figure 4 This is a measured electric field diagram showing the relationship between work area 1 and a high-voltage line at different locations in a certain area of ​​Anhui. Figure 4 The electric field observed repeatedly at point 4510 on line 4820 is affected by high-voltage line interference, resulting in a more dispersed field at high frequencies, but the variation pattern of the electric field curve can still be observed. The electric field observed repeatedly at point 4650 on line 4820 is also affected by intersecting high-voltage lines, resulting in a more dispersed field across the entire frequency band, even influencing the regularity of the electric field variation curve. Points 4550 and 4690 on line 5380, where the MN electrodes receiving the electric field are close to the high-voltage lines, show more concentrated repeated electric field data, largely unaffected by high-voltage line interference.

[0105] Figure 5 This is a measured electric field diagram of a work area in Anhui Province, showing the electric field data at different locations relative to the high-voltage power line. The electric field data at a 44° angle to the high-voltage power line exhibits severe dispersion at frequencies above 10Hz, and a disconnect between high and low frequencies near 1000Hz, failing to accurately reflect the characteristics of the geological strata. However, the electric field data at points nearly perpendicular to the high-voltage power line does not show this disconnect, although the electric field at point 2350 on line 2040, 40 meters from the high-voltage power line, is also relatively dispersed.

[0106] To evaluate the dispersion of data using the root mean square relative difference (RMSD), which can also indirectly reflect the degree of data interference, the RMSD can be calculated using Formula 1 above. Table 1 shows the RMSD relative difference of the electric field at each frequency point 4510 on line 4820, and Table 2 shows the RMSD relative difference of the electric field at each frequency point 4550 on line 5380. As can be seen from Tables 1 and 2, the total RMSD relative difference of the normalized electric field at point 4510 on line 4820 in the same work area is 24.3%, and at point 4550 on line 5380 it is 14.3%. The total RMSD relative difference of the data is significantly increased due to electromagnetic interference caused by high-voltage lines.

[0107] Table 1. Relative difference of root mean square electric field at various frequencies of line 4820 and point 4510.

[0108]

[0109] Table 2. Relative difference of root mean square electric field at various frequencies of line 5380 (4550 points).

[0110]

[0111] Table 3. Relative Difference of Root Mean Square Electric Field under Different Conditions in Two Work Areas in Anhui Province

[0112]

[0113] Table 3 shows the relative differences in the root mean square of the electric field under different conditions in two work areas in a certain area of ​​Anhui. Comparing Table 3 with the above... Figure 4 , Figure 5 After analysis, the following conclusions can be drawn:

[0114] (1) Linear electromagnetic interference sources such as high voltage lines and optical fibers mainly affect the electric field of the measuring electrode at the point where it is not perpendicular to the linear electromagnetic interference source. For example, the electric field of the MN electrode that is close to the high voltage line is more affected by interference than the electric field that is close to the high voltage line.

[0115] (2) The frequency of high-voltage lines that cause major interference to electromagnetic sounding data is mainly concentrated at 48Hz or higher (the frequency closest to the power frequency of the instrument), while the interference to low-frequency data is relatively small, which means that the impact on deep exploration is small.

[0116] (3) In electromagnetic frequency sounding exploration that only measures the amplitude of the electric field, electromagnetic interference manifests as the dispersion of electric field data obtained from multiple measurements, with the data center shifting to higher values. In other words, the interfered electric field data is significantly larger than the normal data, causing the electric field-frequency curve to decouple upwards.

[0117] Example 2 (Interference Suppression)

[0118] Figure 6 This is a diagram showing the interference suppression effect of electric field data from severe electromagnetic interference in a certain area of ​​Shanxi. Figure 7 This is a graph showing the interference suppression effect of electric field data for minor electromagnetic interference in a certain area of ​​Shanxi Province. Figure 6 and Figure 7 It can be seen that the suppression results obtained by multiple averaging and median filtering in the existing technology are not ideal. Figure 6 and Figure 7 The interference estimation filter used in the figure is to select weighted filtering coefficients. As can be seen from the figure, the 50Hz power frequency interference is basically suppressed. Although the high frequency data is still affected by interference, the curve is relatively smooth and can basically reflect the characteristics of the data itself.

[0119] Figure 8 This is an interference suppression effect diagram for two severely electromagnetically interfered measurement points (2800 lines, 2550 points) in a construction area in Anhui Province. Figure 8 As can be seen, the electric field curve obtained by the interference estimation filter of this invention is more reasonable. To evaluate the data characteristics obtained by different processing methods, several simple characteristics are compared here. The sums of the electric fields at each frequency obtained by the average value, ordinary filtering, and interference estimation filtering are 2.213595975, 1.659077978, and 1.519917929 μV·m, respectively. -1 ·A -1 The standard deviations were 0.070, 0.039, and 0.028 μV·m, respectively. -1 ·A-1 As can be seen from the above data, the interference estimation filtering result using the present invention has a smaller value and a smoother electric field-frequency curve, which is consistent with the expectation of suppressing electromagnetic interference data that is significantly larger than normal data.

[0120] In traditional CSAMT exploration or wide-area electromagnetic AB-Ex exploration, the measurement direction of the electric field is limited by the direction of the transmitting source AB. The measured electric field direction (such as Ex) is parallel to known high-voltage lines, telephone lines, and optical fibers, and the data is subject to strong electromagnetic interference. By flexibly measuring the horizontal electric field perpendicular to the main direction of the interference source, the purpose of suppressing electromagnetic interference can be achieved. Figure 9 (Left) is a graph showing the electric field (Ey direction) at a 19-degree angle between the MN electrode and the high-voltage line. Figure 9 (Right) is a graph showing the electric field (Ex direction) at a 71-degree angle between the MN electrode and the high-voltage line. Figure 9 It can be seen that the repeated measurement data in the left graph are more dispersed than those in the right graph, indicating a greater susceptibility to electromagnetic interference. If measurements were taken perpendicular to the high-voltage line, the interference from the line would be significantly reduced. Figure 3 and Figure 4 The effect of MN electrodes on suppressing electromagnetic interference from linear electromagnetic interference sources such as high-voltage lines, telephone lines, and optical fibers can also be observed.

[0121] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A method for identifying and suppressing electromagnetic interference in electromagnetic frequency sounding, characterized in that, Includes the following steps: Repeated data collection is performed for each frequency in the sampling frequency band to obtain the first dataset, and the first electric field-frequency scatter plot is obtained based on the first dataset. Identify whether there are any detached nodes in the first electric field-frequency scatter plot. If so, find the detached nodes in the first electric field-frequency scatter plot. Obtain the normalized electric field of the electromagnetic frequency current for the disconnected and non-disconnected nodes, and obtain the degree of electromagnetic interference of the disconnected node based on the normalized electric field of the electromagnetic frequency current. Determine whether the degree of electromagnetic interference exceeds a threshold. If so, reacquire data through interference suppression to obtain a second dataset. Obtain a second electric field-frequency scatter plot based on the second dataset. Observe whether there are any missing nodes in the second electric field-frequency scatter plot. If not, it is considered that the electromagnetic interference suppression has been completed.

2. The method for identifying and suppressing electromagnetic interference in electromagnetic frequency sounding according to claim 1, characterized in that, The process of identifying whether the second electric field-frequency scatter plot has de-nodes also includes: If so, it is further determined whether the number of detached nodes in the second electric field-frequency scatter plot exceeds the threshold. If not, it is considered that the suppression of electromagnetic interference has been completed. If so, data is reacquired through interference suppression until the suppression of electromagnetic interference is completed.

3. The method for identifying and suppressing electromagnetic interference in electromagnetic frequency sounding according to claim 1, characterized in that, When repeatedly collecting data for each frequency, the following is included: Preset the first number of samples, the second number of samples, the first frequency band value, and the second frequency band value; Determine whether each frequency in the sampling frequency band is at the value of the first frequency band or the value of the second frequency band; If the frequency is within the first frequency band, then the frequency is repeatedly sampled according to the first number of samples. If the frequency is in the second frequency band, then the frequency is repeatedly sampled according to the second sampling number.

4. The method for identifying and suppressing electromagnetic interference in electromagnetic frequency sounding according to claim 1, characterized in that, When obtaining the degree of electromagnetic interference experienced by the disconnected node based on the normalized electric field of the electromagnetic frequency current, the following is included: Obtain the root mean square relative difference of the electromagnetic frequency current normalized electric field for each of the said de-nodes, and obtain the total root mean square relative difference of the de-nodes based on the root mean square difference of all the said de-nodes. Obtain the root mean square relative difference of the electromagnetic frequency current normalized electric field for each of the non-detached nodes, and obtain the total root mean square relative difference of the non-detached nodes based on the root mean square difference of all the non-detached nodes. Obtain the difference between the total root mean square relative difference of the nodes that have been removed and the total root mean square relative difference of the nodes that have not been removed; The difference represents the degree of electromagnetic interference experienced by the disconnected node.

5. The method for identifying and suppressing electromagnetic interference in electromagnetic frequency sounding according to claim 4, characterized in that, When obtaining the root-mean-square relative difference between the normalized electric field of the electromagnetic frequency current for the disconnected and non-disconnected nodes, the following steps are included: Based on the normalized electric field of the current collected from the detached node and the non-detached node, and the mean value of the normalized electric field of the current measured from each detached node and the non-detached node, the root mean square relative difference of the electromagnetic frequency current normalized electric field between the detached node and the non-detached node is obtained, as shown in Formula 1: （1） In the formula, For frequency point No. The normalized electric field of the current obtained from the second sampling. For frequency point The mean of the normalized electric field for each measured current.

6. The method for identifying and suppressing electromagnetic interference in electromagnetic frequency sounding according to claim 1, characterized in that, When reacquiring data through interference suppression, the following are included: Based on the acquisition area of ​​the first dataset, a region closer to the field source is determined to carry out electric field data acquisition, thereby improving the signal-to-noise ratio of the acquired data and suppressing electromagnetic interference.

7. The method for identifying and suppressing electromagnetic interference in electromagnetic frequency sounding according to claim 1, characterized in that, When reacquiring data through interference suppression, the following are included: Set the initial electric field value at the frequency point, and obtain the filter coefficient of each measurement data based on the difference between each measurement data and the initial electric field value; The initial electric field value is iteratively updated based on the filter coefficients of each measurement data to obtain data that is closer to the true electric field value.

8. The method for identifying and suppressing electromagnetic interference in electromagnetic frequency sounding according to claim 1, characterized in that, When reacquiring data through interference suppression, the following are included: By incorporating data from surrounding frequency points in the first dataset, interference estimation filtering is performed, as shown in Formula 2: （2）； In the formula, The number of frequency points involved in the filtering calculation. Repeat the electric field measurement a number of times for each frequency point. These are the filter coefficients. For the first The frequency point The electric field was measured once.

9. The method for identifying and suppressing electromagnetic interference in electromagnetic frequency sounding according to claim 1, characterized in that, When reacquiring data through interference suppression, the following are included: Identify the interference source causing electromagnetic interference to the first dataset, obtain the main direction of the interference source, and repeatedly collect data for each frequency perpendicular to the main direction of the interference source to suppress the electromagnetic interference from the interference source.

10. A system for identifying and suppressing electromagnetic interference in electromagnetic frequency sounding, characterized in that, include: Acquisition unit: used to repeatedly acquire data for each frequency in the sampling frequency band to obtain a first dataset, and to obtain a first electric field-frequency scatter plot based on the first dataset; Identification unit: used to identify whether there are any detached nodes in the first electric field-frequency scatter plot; if so, to find the detached nodes in the first electric field-frequency scatter plot. Interference level acquisition unit: used to acquire the normalized electric field of electromagnetic frequency current for the disconnected node and the non-disconnected node, and to obtain the degree of electromagnetic interference of the disconnected node based on the normalized electric field of electromagnetic frequency current. Interference suppression unit: used to determine whether the degree of electromagnetic interference exceeds the threshold. If so, the data is reacquired through interference suppression to obtain a second dataset. A second electric field-frequency scatter plot is obtained based on the second dataset. The second electric field-frequency scatter plot is observed to see if there are any missing nodes. If not, the electromagnetic interference suppression is considered to be complete.

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