Very-low-frequency emission source positioning method and system based on three foundation observation stations

Abstract

The invention provides a very-low-frequency emission source positioning method and system based on three foundation observation stations. The method comprises the following steps: deploying a very-low-frequency signal emission source positioning system based on the three foundation observation stations; starting a very-low-frequency signal emission source positioning system, and enabling each ground-based observation station to enter a conventional operation state; after all the ground-based observation stations complete direction-finding result verification, determining direction-finding receiving data of each ground-based observation station; selecting an effective observation station pair according to the direction-finding receiving data, and obtaining effective observation data of the effective observation station pair; and performing center cross positioning evaluation by using the effective observation data, and determining the position information of the very-low-frequency emission source. According to the method, the multi-site cooperative positioning technology is utilized, monitoring and positioning of the very-low-frequency signal emission source can be efficiently completed in real time without a monitoring blind area, and the method has the advantages of being simple in calculation, rapid in processing and high in precision and can be widely applied to the fields of electromagnetic signal detection, electromagnetic environment and earthquake precursor research and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of very low frequency (VLF) detection and applications, and particularly to a method and system for locating VLF emission sources based on three ground-based observation stations. Background Art

[0002] Very Low Frequency (VLF) waves are electromagnetic waves with a frequency range of 3 - 30 kHz, characterized by long wavelengths and low propagation attenuation. The typical attenuation coefficient is about 2 - 3 dB / Mm. VLF waves propagate in the Earth-ionosphere waveguide and can achieve ultra-long-distance propagation, which makes them have important application values in fields such as communication, space environment monitoring, and signal source location. The propagation characteristics of VLF waves are closely related to the electron density of the D layer in the ionosphere. The D layer of the ionosphere is located in the altitude range of 60 - 100 kilometers above the ground and is a partially ionized layer of the atmosphere, with its electron density usually between 1 - 1000 cm-3. The D layer is affected both by the top-down influence of solar activity and the bottom-up perturbation of atmospheric fluctuations, so its electron density will change dynamically, thus directly affecting the propagation effect of VLF waves.

[0003] The sources of VLF waves mainly include natural thunderstorm activities and artificial transmitting stations. VLF waves generated by natural thunderstorms are commonly used for signal detection of lightning activities, while artificial transmitting stations, with their stable signal emission capabilities, are widely used in long-distance communication and space environment monitoring. Whether from natural or artificial sources, the directional characteristics and time-delay information of VLF wave signals provide an important basis for high-precision signal source location.

[0004] Current signal location technologies are gradually developing from single-point reference methods to multi-point collaborative direction finding. Traditional single-point methods are vulnerable to noise interference and environmental changes due to limited information, resulting in insufficient location accuracy. However, the azimuth cross-location technology based on multi-point collaboration can significantly improve location accuracy and robustness by integrating the directional data of multiple receiving points and combining optimization algorithms. In signal source location, this technology can effectively achieve high-efficiency location of dynamic signal sources by extracting the direction data of target signals, providing a reliable solution for application requirements in complex environments. Summary of the Invention

[0005] The present invention provides a method and system for locating VLF emission sources based on three ground-based observation stations to solve the defects existing in the prior art.

[0006] In a first aspect, the present invention provides a method for locating VLF emission sources based on three ground-based observation stations, including:

[0007] Deploy a VLF signal emission source location system based on three ground-based observation stations;

[0008] Start the very low frequency (VLF) signal emitter positioning system to bring each ground-based observation station into normal operation status;

[0009] After all ground-based observation stations have completed the verification of the direction finding results, determine the direction finding reception data of each ground-based observation station;

[0010] Select effective observation station pairs according to the direction finding reception data, and obtain the effective observation data of the effective observation station pairs;

[0011] Use the effective observation data for central intersection positioning evaluation to determine the position information of the VLF emitter.

[0012] According to a VLF emitter positioning method based on three ground-based observation stations provided by the present invention, deploy a VLF signal emitter positioning system based on three ground-based observation stations, including:

[0013] The first ground-based observation station, the second ground-based observation station, the third ground-based observation station and the central processing server. Each ground-based observation station includes four loop antennas, a four-channel receiver and a host computer;

[0014] The four loop antennas are respectively arranged in the north-south direction, the east-west direction, the northeast-southwest direction deflected by 45 degrees and the northwest-southeast direction deflected by 45 degrees for receiving VLF signals in different directions;

[0015] Collect the VLF signals through the four-channel receiver, and extract the amplitude characteristics and phase characteristics;

[0016] The host computer performs directional analysis and direction finding evaluation on the VLF signal of the specified frequency and outputs the direction finding result;

[0017] Transmit the direction finding result to the central processing server for processing through Internet encryption.

[0018] According to a VLF emitter positioning method based on three ground-based observation stations provided by the present invention, start the VLF signal emitter positioning system to bring each ground-based observation station into normal operation status, including:

[0019] After the VLF signal emitter positioning system is started, three ground-based observation stations perform real-time direction finding on the VLF signal of the specified frequency;

[0020] Each ground-based observation station outputs the direction angle of the target signal, the timestamp and the longitude and latitude position information of the observation station.

[0021] According to a VLF emitter positioning method based on three ground-based observation stations provided by the present invention, select effective observation station pairs according to the direction finding reception data, and obtain the effective observation data of the effective observation station pairs, including:

[0022] Determine the first direction angle, the second direction angle, and the third direction angle corresponding to three ground-based observation stations respectively;

[0023] Calculate the first direction angle difference between the first direction angle and the second direction angle, calculate the second direction angle difference between the first direction angle and the third direction angle, and calculate the third direction angle difference between the second direction angle and the third direction angle. All direction angle differences are within the range of 0 degrees to 180 degrees;

[0024] Compare the three direction angle differences, and select the two sets of ground-based observation stations with the largest direction angle difference as the effective observation station pairs;

[0025] Obtain the observation station longitude and latitude coordinates and direction angle data of the effective observation station pairs, discard the direction finding results of the third station, and re-determine the effective observation station pairs as the new first ground-based observation station and the second ground-based observation station.

[0026] According to a very low frequency emission source positioning method based on three ground-based observation stations provided by the present invention, comparing the three direction angle differences and selecting the two sets of ground-based observation stations with the largest direction angle difference as the effective observation station pairs includes:

[0027] If it is determined that the first direction angle difference is the largest, determine the first ground-based observation station and the second ground-based observation station as the effective observation station pair;

[0028] If it is determined that the second direction angle difference is the largest, determine the first ground-based observation station and the third ground-based observation station as the effective observation station pair;

[0029] If it is determined that the third direction angle difference is the largest, determine the second ground-based observation station and the third ground-based observation station as the effective observation station pair.

[0030] According to a very low frequency emission source positioning method based on three ground-based observation stations provided by the present invention, using the effective observation data to perform central cross-positioning evaluation to determine the very low frequency emission source position information, including:

[0031] Step 1, determine that the geographical coordinates of the first ground-based observation station are A(lat1, lon1), and the geographical coordinates of the second ground-based observation station are B(lat2, lon2). The geographical coordinates of the emission station to be determined are C(lat3, lon3). The azimuth angles of point C relative to points A and B are set as θ1 and θ2;

[0032] Step 2, solve the approximate result of point C through a plane rectangular coordinate system to obtain point C1;

[0033] Step 3: Let the distances from C1 to points A and B be L1 and L2. If both L1 and L2 are less than the preset distance, replace the great circle coordinate system with a rectangular coordinate system and use the coordinates of C1 as the coordinate position of point C; otherwise, proceed to the subsequent steps.

[0034] Step 4: If both L1 and L2 are greater than the preset distance, it is determined that the distances from point C1 solved in the rectangular coordinate system to points A and B are shorter than the distances from the actual point C to A and B. Draw great circle paths with points A and B as the starting points and θ1 and θ2 as the azimuth angles, draw great circle paths of a specified length, and obtain the end coordinates A1 and B1 of the two great circle paths.

[0035] Step 5: Replace the original points A and B with the obtained A1 and B1, and repeat Steps 2 to 5 until both L1 and L2 are less than the preset distance, and output the final result.

[0036] According to a very low frequency emission source positioning method based on three ground-based observation stations provided by the present invention, Step 2 includes:

[0037] Step 21: According to the azimuth angle θ1, assume the length of AC is r1, then the coordinates (x1, y1) of point C in the plane rectangular coordinate system are expressed as:

[0038] x1 = r1sinθ1, y1 = r1cosθ1

[0039] Step 22: For the coordinates (x B , y B ) of point B, according to the azimuth angle θ2 and assuming the length of BC is r2, the coordinates (x2, y2) of point C are expressed as:

[0040] x2 = x B + r2sinθ2, y2 = y B + r2cosθ2

[0041] Step 23: Solve the simultaneous equations to obtain r1 and r2;

[0042] Step 24: After obtaining the coordinates of point C in the approximate plane rectangular coordinate system, convert them back to geographical coordinates. The conversion formula is as follows:

[0043] Assume the coordinates of point C in the plane rectangular coordinate system are (x, y), then its latitude is and its longitude is where R is the radius of the earth.

[0044] According to a very low frequency emission source positioning method based on three ground-based observation stations provided by the present invention, Step 3 includes:

[0045] Step 31: Calculate the distances between C1 and points A and B according to the great circle distance formula. The formula is as follows:

[0046] Assume to find the distance between point A j (lat j , lon j ) and point B k (lat k , lon k ), Dis:

[0047] a = (sin(Deg(lat j - lat k )) / 2)^2 2 + cos(Deg(lat j )) × cos(Deg(lat k ))

[0048] ×(sin(Deg(lon j - lon k )) / 2)^2 2

[0049]

[0050] where a is an intermediate variable algebra, and Deg is a function for converting longitude and latitude to radians. The specific function is as follows:

[0051] lat_rad = lat × π / 180

[0052] where lat_rad is in radians and lat is in degrees;

[0053] Step 32: The very low frequency (VLF) signal frequency range is 3 - 30 kHz, corresponding to a wavelength length of 10 - 100 km. If L1 and L2 are within the preset distance range, then under the current conditions, the rectangular coordinate system can be used to replace the great circle coordinate system for calculation and solution, that is, the result calculated in Step 2 is within the error range. Under normal circumstances, L1 and L2 are much larger than the preset distance.

[0054] According to a VLF transmitter positioning method based on three ground-based observation stations provided by the present invention, Step 4 includes:

[0055] Step 41: Draw two great circle paths with the lengths of L1 and L2. The longitude and latitude coordinates of their endpoints are calculated by the following formula:

[0056] Taking the starting point A(lat1, lon1) and azimuth angle θ1 as an example, the endpoint coordinates are A1(lat11, lon11)

[0057] lat 11= arcsin(sin(lat_rad1)×cos(L1 / R)

[0058] + cos(lat_rad1)×sin(L1 / R)×cos(θ_rad1))

[0059] lon 11 = lon_rad1 + arctan2(sin(θ_rad1)×sin(L1 / R)×cos(lat_rad1),

[0060] cos(L1 / R) - sin(lat_rad1)×sin(lat 11 ))

[0061] where lat_rad1, lon_rad1, and θ_rad1 are the latitude and longitude of point A and the result of converting θ1 to radians, and R is the radius of the earth.

[0062] In a second aspect, the present invention further provides a very low frequency emission source positioning system based on three ground-based observation stations, including:

[0063] A deployment module for deploying a very low frequency signal emission source positioning system based on three ground-based observation stations;

[0064] A start module for starting the very low frequency signal emission source positioning system to enable each ground-based observation station to enter a normal operation state;

[0065] A verification module for determining the direction finding reception data of each ground-based observation station after all ground-based observation stations have completed the verification of the direction finding results;

[0066] A selection module for selecting valid observation station pairs according to the direction finding reception data and obtaining the valid observation data of the valid observation station pairs;

[0067] A positioning module for using the valid observation data to perform a central intersection positioning evaluation to determine the position information of the very low frequency emission source.

[0068] The VLF emission source localization method and system based on three ground-based observation stations provided by the present invention can collect the VLF wave directivity data by deploying multiple receiving stations, and use the cross-location algorithm and signal fusion processing technology to determine the position of the emission source in real time under complex electromagnetic environments. Compared with traditional methods, this method significantly reduces the localization error and improves the real-time performance and stability of the localization system. The present invention can be widely applied to the high-precision localization of signal sources, such as the monitoring of lightning signal sources in thunderstorm activities, the precise localization of artificial VLF emission stations, and the source analysis of ionospheric disturbance signal sources. Through the in-depth exploration of VLF signal characteristics and the innovation of optimization algorithms, the present invention provides a new technical framework for VLF signal localization technology, which can effectively meet the requirements of real-time localization of dynamic targets and provide strong support for high-precision localization projects and related scientific research. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0070] Figure 1 is one of the schematic flowcharts of the VLF emission source localization method based on three ground-based observation stations provided by the present invention;

[0071] Figure 2 is the structural diagram of the VLF signal emission source localization system based on three ground-based observation stations provided by the present invention;

[0072] Figure 3 is the second schematic flowchart of the VLF emission source localization method based on three ground-based observation stations provided by the present invention;

[0073] Figure 4 is the structural schematic diagram of the VLF emission source localization system based on three ground-based observation stations provided by the present invention;

[0074] Figure 5 is the structural schematic diagram of the electronic device provided by the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0075] To make the objectives, technical solutions, and advantages of the present invention clearer, the following will clearly and completely describe the technical solutions in the present invention in conjunction with the drawings in the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art without creative efforts based on the embodiments in the present invention fall within the protection scope of the present invention.

[0076] Figure 1 It is one of the flow schematic diagrams of the very low frequency (VLF) emission source localization method based on three ground-based observation stations provided by an embodiment of the present invention. As Figure 1 shown, it includes:

[0077] Step 100: Deploy a VLF signal emission source localization system based on three ground-based observation stations;

[0078] Step 200: Start the VLF signal emission source localization system to make each ground-based observation station enter the normal operation state;

[0079] Step 300: After all ground-based observation stations complete the verification of the direction finding results, determine the direction finding and receiving data of each ground-based observation station;

[0080] Step 400: Select valid observation station pairs according to the direction finding and receiving data, and obtain the valid observation data of the valid observation station pairs;

[0081] Step 500: Use the valid observation data to perform central cross-positioning evaluation to determine the position information of the VLF emission source.

[0082] Specifically, the embodiment of the present invention adopts a VLF signal emission source localization system based on three ground-based observation stations as Figure 2 shown. The system consists of 3 ground-based receiving stations (VLF Station 1, VLF Station 2, and VLF Station 3) and 1 central processing server (Server). Each receiving station is equipped with 4 loop antennas, which are respectively arranged in the north-south (N-S), east-west (E-W), and northeast-southwest (NE-SW) and northwest-southeast (NW-SE) directions deflected by 45°, constituting an omnidirectional receiving system for capturing VLF signals in different directions. The signals are collected by a four-channel receiver and the amplitude and phase characteristics are extracted, and the host computer performs directional analysis and direction finding evaluation on the signals of the specified frequency. The direction finding results are encrypted and transmitted to the central server through the Internet. The central server selects the required signal pairs based on the direction finding results of each receiving station and runs the cross-positioning algorithm, comprehensively analyzes the directional information of the signals, and accurately calculates the position of the emission source.

[0083] To meet the high-precision positioning requirements of very low frequency (VLF) signal emission sources, the present invention proposes the deployment requirements for three observation stations to ensure the direction-finding accuracy and positioning stability of the system. First of all, the observation stations need to be deployed in an equilateral triangle configuration, and the spacing between the stations needs to reach the order of thousands of kilometers. This geometric layout can maximize the coverage of the target area and effectively reduce the positioning error by increasing the geometric baseline length of cross-location. In addition, the equilateral triangle layout can also ensure the complementarity of the observation directions of each station, providing ideal geometric conditions for multi-point collaborative positioning.

[0084] Secondly, the antennas of the observation stations need to have a high degree of directivity. The directivity error must be controlled within a small range, and at the same time, the polarities of all antennas need to be consistent to ensure the consistency of the phase and direction information of the received signals. This precise design of antenna directivity and polarity consistency is the key to achieving high-precision direction finding and signal fusion processing, which can significantly improve the positioning accuracy and reliability of the system, especially showing strong robustness in complex electromagnetic environments.

[0085] Furthermore, as Figure 3 shown, the present invention proposes a cross-location method that utilizes the very low frequency direction-finding results of two effective responses. This algorithm runs on the central server to estimate the position information of the signal source, and specifically includes the following steps:

[0086] The first step, system startup and data processing

[0087] First of all, start the positioning system to ensure that each observation station enters the normal operation state. After the system starts, the three observation stations will perform real-time direction finding on the very low frequency signals of the specified frequency and transmit the direction-finding results to the central server through an encrypted network. Each observation station needs to provide the following direction-finding data: the direction angle (azimuth angle) of the target signal, the timestamp, and the longitude and latitude position information of the observation station. The timestamp is used to ensure that the direction-finding results of the three observation stations correspond to the same signal event, thus ensuring the timeliness and consistency of the data. Time synchronization can be achieved through high-precision timekeeping technologies (such as GNSS timekeeping) to eliminate the impact of the time difference between stations on the positioning accuracy.

[0088] The second step, receive and synchronize the direction-finding data

[0089] After the direction-finding results of all observation stations are verified, they are transmitted to the central server as the basic data for the subsequent cross-location algorithm. This process provides high-precision and synchronized directionality information input for the positioning system, laying a solid foundation for the real-time precise positioning of the signal source.

[0090] The third step, select effective observation station pairs

[0091] (1) Calculate the direction angle difference

[0092] From the direction angle data (denoted as θ A , θ B and θ C ) of three observation stations (denoted as A, B, and C), calculate the direction angle differences between pairwise stations (denoted as Δθ AB , Δθ AC and Δθ BC ), which are defined as:

[0093] Δθ AB = |θ A - θ B |, Δθ AC = |θ A - θ C |, Δθ BC = |θ B - θ c |

[0094] The direction angle difference is limited within the range of [0°, 180°] to ensure the correctness of the direction information.

[0095] (2) Select the pair of stations with the largest direction angle difference

[0096] Compare the three direction angle differences and select the two pairs of observation stations with the largest difference as the effective observation station pairs. The rules are as follows:

[0097] If Δθ AB is the largest, then select stations A and B;

[0098] If Δθ AC is the largest, then select stations A and C;

[0099] If Δθ BC is the largest, then select stations B and C.

[0100] By selecting the pair of stations with the largest direction angle difference, the geometric stability of cross - positioning is ensured, avoiding a large increase in positioning error caused by collinearity, that is, the geometric positions of the emission source and the two receiving stations are close to a straight line.

[0101] (3) Record the data of the effective observation stations

[0102] Record the longitude and latitude coordinates and the corresponding direction angle data of the two selected effective observation stations, and discard the direction - finding results of the third station to reduce redundant calculations. And re - denote the two effective observation stations as A and B respectively.

[0103] Step 4: Perform cross - positioning evaluation processing on the central server

[0104] Step 1: Assume that the geographical coordinates of the two receiving stations are A(lat1,lon1) and B(lat2,lon2), and the position of the transmitting station to be obtained is set to C(lat3,lon3); the azimuth of point C relative to points A and B is set to θ1 and θ2;

[0105] Step 2, solve the approximate result through the plane rectangular coordinate system, and set the result obtained in step 2 as point C1;

[0106] Step 21. According to the azimuth angle θ1, let the length of AC be r1, then the coordinates (x1, y1) of point C in this plane rectangular coordinate system can be expressed as:

[0107] x1=r1sinθ1,y1=r1cosθ1

[0108] Step 22: For the coordinates of point B (x B ,y B ), according to the azimuth angle θ2 and the assumed length r2 of BC, the coordinates of point C (x2, y2) can be expressed as:

[0109] x2=x B +r2sinθ2,y2=y B +r2cosθ2

[0110] Step 23, then solve the equations Solve for r1 and r2;

[0111] Step 24: After obtaining the coordinates of point C in this approximate plane rectangular coordinate system, convert them back to geographic coordinates. The conversion formula is as follows:

[0112] Let the coordinates of point C in the plane rectangular coordinate system be (x, y), then its latitude longitude (R is the radius of the earth).

[0113] Step 3: According to the result calculated in step 2, let the distance between C1 and points A and B be L1 and L2. Condition 1: L1 and L2 are both <1km. Under this condition, the rectangular coordinate system can replace the great circle coordinate system, that is, the coordinates of C1 can be used as the coordinate position of point C. Condition 2: If condition 1 is not met, proceed to the subsequent steps.

[0114] Step 31, calculate the distance between C1 and points A and B according to the great circle distance formula. The formula is as follows: Assume that A j (lat j ,lon j ) and B k (lat k ,lon k ) between:

[0115] a = (sin(Deg(lat j - lat k )) / 2)) 2 + cos(Deg(lat j )) × cos(Deg(lat k ))

[0116] × (sin(Deg(lon j - lon k )) / 2)) 2

[0117]

[0118] Where a is the intermediate variable algebra, and Deg is the radian system function for calculating longitude and latitude. The specific function is as follows:

[0119] lat_rad = lat × π / 180

[0120] Where lat_rad is in the radian system and lat is in degrees;

[0121] Step 32: The very low frequency signal frequency range is 3 - 30 kHz, and its wavelength length is 10 - 100 km. If L1 and L2 are within 1 km, then under the current conditions, the rectangular coordinate system can replace the great circle coordinate system for calculation and solution, that is, the result calculated in Step 2 is the result within the error range. Under normal circumstances, L1, L2 >> 1 km;

[0122] Step 4: When L1, L2 > 1 km, it can be known that the distances from point C1 solved in the rectangular coordinate system to points A and B are shorter than the distances from the actual point C to A and B. Respectively draw great circle paths with points A and B as the starting points and θ1 and θ2 as the azimuth angles, draw great circle paths of a specified length, and obtain the end coordinates A1 and B1 of the two great circle paths;

[0123] Step 41: Draw two great circle paths with the lengths of L1 and L2, and the longitude and latitude coordinates of their ends are calculated by the following formula: Taking the starting point A(lat1, lon1) and the azimuth angle θ1 as an example, the end coordinate is A1(lat11, lon11)

[0124]

[0125] Where lat_rad1, lon_rad1, and θ_rad1 are the longitude and latitude of point A and the result of converting θ1 to the radian system, and R is the radius of the earth.

[0126] Step 5: Replace the original points A and B with the obtained A1 and B1, and repeat Steps 2, 3, 4, and 5 until the condition 1 in Step 3 is met, that is, output the position of C1 as the result.

[0127] The following uses an embodiment to illustrate the method flow of the present invention, including:

[0128] Step 1: Determine the position of the receiving station and the emission angles of the signals received by each receiving station. In this embodiment, two stations, SZ(31.5657, 113.3181) and DC(29.3543, 100.1435), are regarded as effective very low frequency observation stations.

[0129] Step 11: Assume that two known receiving stations are A and B, and their corresponding geographical coordinates are A(lat1, lon1) and B(lat2, lon2). The position of the transmitting station to be obtained is set as C(lat3, lon3); the azimuth angles of point C relative to points A and B are set as θ1 and θ2; solve the coordinate position of point C under the condition that the coordinates of A and B and the values of θ1 and θ2 are known.

[0130] Step 2: Solve the approximate result through the plane rectangular coordinate system, and the result obtained in Step 2 is set as point C1.

[0131] Step 3: Make a judgment based on the result calculated in Step 2. Let the distances between C1 and points A and B be L1 and L2. Condition 1: Both L1 and L2 are < 1 km. Under this condition, the rectangular coordinate system can replace the great circle coordinate system, that is, the coordinates of C1 can be used as the coordinate position of point C. Condition 2: If Condition 1 is not met, then perform the subsequent steps.

[0132] Step 32: The frequency range of the very low frequency signal is 3 - 30 kHz, and its wavelength length is 10 - 100 km; if L1 and L2 are within the range of 1 km, then under the current condition, the rectangular coordinate system can replace the great circle coordinate system for calculation and solution, that is, the result calculated in Step 2 is the result within the error range; generally, L1 and L2 >> 1 km.

[0133] Step 4: When L1 and L2 > 1 km, it can be known that the distances from point C1 solved by the rectangular coordinate system to points A and B are shorter than the distances from the actual point C to points A and B; respectively draw great circle paths with points A and B as the starting points and θ1 and θ2 as the azimuth angles, draw great circle paths with a specified length, and obtain the end coordinates A1 and B1 of the two great circle paths.

[0134] Step 5: Replace the original points A and B with the obtained A1 and B1, and repeat Steps 2, 3, 4, and 5 until the condition 1 in Step 3 is met, that is, output the final result; verification example:

[0135] Specifically, in the embodiments of the present invention, the receiving station located at DC(29.3543,100.1435) is used as Station A, and the receiving station located at SZ(31.5657,113.3181) is used as Station B. Taking three very low frequency (VLF) transmitting stations NWC(-21.8,114.15), JJI(32.4,130.49) and VTX(8.2,77.46) that need to be calculated as the transmitting stations at Point C to be solved as an example;

[0136] The results obtained by using the method of the present invention to calculate the coordinates of the three transmitting stations are (-21.79994,114.14998) with an error of 6.984 m, (32.400005,130.49007) with an error of 6.595 m, and (8.20002,77.46003) with an error of 3.98 m respectively; the calculation times are 9.64 s, 9.63 s and 9.62 s respectively; which proves the feasibility of this method;

[0137] The present invention provides a transmitting source positioning system and method based on three ground very low frequency (VLF) observation stations, aiming to accurately locate the transmitting source through a high-precision positioning algorithm. The system consists of three observation stations deployed in a large-spacing regular triangle pattern and a central processing server, which can collect VLF signals with high precision and evaluate the direction of signals at a specified frequency through a host computer. The measurement results are encrypted and transmitted via the Internet to the central server for processing. The central server uses the received angle information and the location data of the receiving stations, and adopts a cross-location algorithm to accurately calculate the geographical location of the transmitting source. This method first solves the preliminary positioning result through a plane rectangular coordinate system, and performs multiple iterative optimizations through the great circle path segmentation method, and finally outputs a positioning result that meets the accuracy requirements. Compared with the traditional method, the present invention has the characteristics of simple and efficient calculation process and high positioning accuracy. Through multiple observation stations and accurate positioning algorithms, the present invention significantly improves the positioning accuracy of VLF signal sources, can effectively reduce the positioning error, and is applicable to fields such as electromagnetic environment monitoring, signal source positioning, and very low frequency signal detection. This system is particularly suitable for scenarios such as military reconnaissance, marine exploration, and electromagnetic environment monitoring, and has important military and civilian values. The system requires that the three ground observation stations be arranged in a regular triangle pattern and maintain a large spacing to ensure the high-precision positioning of the signal source. At the same time, the measurement results need to be transmitted via the Internet, so a stable network environment is required. Although the system has strong environmental adaptability, it still needs to be appropriately calibrated and optimized in a high electromagnetic interference environment to ensure the accurate reception of signals. This invention has significant significance in improving the accuracy of electromagnetic monitoring and promoting the application of VLF signal technology. At the same time, it can provide technical support in multiple fields such as military, security, and resource exploration, and promote the progress and development of related industries.

[0138] The very low frequency (VLF) emission source positioning system based on three ground-based observation stations provided by the present invention will be described below. The VLF emission source positioning system based on three ground-based observation stations described below can be referred to in correspondence with the VLF emission source positioning method based on three ground-based observation stations described above.

[0139] Figure 4 FIG. is a schematic structural diagram of the VLF emission source positioning system based on three ground-based observation stations provided by an embodiment of the present invention. As Figure 4 shown, it includes: a deployment module 91, a start module 92, a verification module 93, a selection module 94, and a positioning module 95, where:

[0140] The deployment module 91 is used to deploy the VLF signal emission source positioning system based on three ground-based observation stations; the start module 92 is used to start the VLF signal emission source positioning system to make each ground-based observation station enter the normal operation state; the verification module 93 is used to determine the direction finding reception data of each ground-based observation station after all ground-based observation stations complete the verification of the direction finding results; the selection module 94 is used to select valid observation station pairs according to the direction finding reception data and obtain the valid observation data of the valid observation station pairs; the positioning module 95 is used to perform central intersection positioning evaluation using the valid observation data to determine the position information of the VLF emission source.

[0141] Figure 5 FIG. illustrates a schematic structural diagram of an electronic device. As Figure 5 shown, the electronic device may include: a processor 1010, a communication interface 1020, a memory 1030, and a communication bus 1040. Among them, the processor 1010, the communication interface 1020, and the memory 1030 communicate with each other through the communication bus 1040. The processor 1010 can call the logical instructions in the memory 1030 to execute the VLF emission source positioning method based on three ground-based observation stations. The method includes: deploying the VLF signal emission source positioning system based on three ground-based observation stations; starting the VLF signal emission source positioning system to make each ground-based observation station enter the normal operation state; determining the direction finding reception data of each ground-based observation station after all ground-based observation stations complete the verification of the direction finding results; selecting valid observation station pairs according to the direction finding reception data and obtaining the valid observation data of the valid observation station pairs; performing central intersection positioning evaluation using the valid observation data to determine the position information of the VLF emission source.

[0142] In addition, when the logical instructions in the above-mentioned memory 1030 are implemented in the form of software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on such an understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or a part of this technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in various embodiments of the present invention. The aforementioned storage medium includes: various media that can store program codes, such as USB flash drives, mobile hard disks, read-only memories (ROM, Read-Only Memory), random access memories (RAM, Random Access Memory), magnetic disks, or optical discs.

[0143] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed to multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment. Those of ordinary skill in the art can understand and implement it without creative labor.

[0144] Through the description of the above embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus a necessary general hardware platform, and of course, it can also be implemented by hardware. Based on such an understanding, the technical solution, in essence, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disks, optical discs, etc., and includes several instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to execute the methods described in various embodiments or some parts of the embodiments.

[0145] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments or perform equivalent replacements for some of the technical features. These modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of various embodiments of the present invention.

Claims

1. A very low frequency emission source positioning method based on three ground-based observation stations, characterized in that, Including: Deploy a very low frequency (VLF) signal transmitter positioning system based on three ground-based observation stations; Start the VLF signal transmitter positioning system to make each ground-based observation station enter the normal operation state; After all ground-based observation stations complete the verification of the direction finding results, determine the direction finding and receiving data of each ground-based observation station; Select valid observation station pairs according to the direction finding and receiving data, and obtain the valid observation data of the valid observation station pairs; Use the valid observation data to conduct a central intersection positioning evaluation to determine the position information of the VLF transmitter.

2. The very low frequency emission source localization method based on three ground-based observation stations according to claim 1, characterized in that Deploy a VLF signal transmitter positioning system based on three ground-based observation stations, including: The first ground-based observation station, the second ground-based observation station, the third ground-based observation station, and the central processing server. Each ground-based observation station includes four loop antennas, a four-channel receiver, and a host computer; The four loop antennas are respectively arranged in the north-south direction, the east-west direction, the northeast-southwest direction deflected by 45 degrees, and the northwest-southeast direction deflected by 45 degrees for receiving VLF signals in different directions; Collect the VLF signals through the four-channel receiver, and extract the amplitude characteristics and phase characteristics; The host computer conducts directional analysis and direction finding evaluation on the VLF signals of the specified frequency and outputs the direction finding results; Transmit the direction finding results to the central processing server for processing through Internet encryption.

3. The very low frequency emission source localization method based on three ground-based observation stations according to claim 1, characterized in that Start the VLF signal transmitter positioning system to make each ground-based observation station enter the normal operation state, including: After the VLF signal transmitter positioning system is started, three ground-based observation stations conduct real-time direction finding on the VLF signals of the specified frequency; Each ground-based observation station outputs the direction angle of the target signal, the timestamp, and the longitude and latitude position information of the observation station.

4. The very low frequency emission source localization method based on three ground-based observation stations according to claim 1, characterized in that Select valid observation station pairs according to the direction finding and receiving data, and obtain the valid observation data of the valid observation station pairs, including: Determine the first direction angle, the second direction angle, and the third direction angle corresponding to the three ground-based observation stations respectively; Calculate the first direction angle difference between the first direction angle and the second direction angle, calculate the second direction angle difference between the first direction angle and the third direction angle, calculate the third direction angle difference between the second direction angle and the third direction angle, and all direction angle differences are within the range of 0 degrees to 180 degrees; Compare the three direction angle differences, and select the two groups of ground-based observation stations with the largest direction angle difference as the valid observation station pairs; Obtain the longitude and latitude coordinates and direction angle data of the observation stations of the valid observation station pairs, discard the direction finding results of the third station, and re-determine the valid observation station pairs as the new first ground-based observation station and the second ground-based observation station.

5. The VLF transmitter positioning method based on three ground-based observation stations according to claim 4, wherein Compare the three direction angle differences, and select the two groups of ground-based observation stations with the largest direction angle difference as the valid observation station pairs, including: If it is determined that the first direction angle difference is the largest, determine the first ground-based observation station and the second ground-based observation station as the valid observation station pairs; If it is determined that the second direction angle difference is the largest, determine the first ground-based observation station and the third ground-based observation station as the valid observation station pairs; If it is determined that the third direction angle difference is the largest, determine the second ground-based observation station and the third ground-based observation station as the valid observation station pairs.

6. The very low frequency emission source localization method based on three ground-based observation stations according to claim 1, characterized in that, Performing central intersection positioning evaluation using the effective observation data to determine the position information of the very low frequency emission source, including: Step 1, determine that the geographical coordinates of the first ground-based observation station are A(lat1, lon1), and the geographical coordinates of the second ground-based observation station are B(lat2, lon2). The geographical coordinates of the position of the transmitting station to be determined are C(lat3, lon3). The azimuth angles of point C relative to points A and B are set as θ 1 and θ 2; Step 2: Solve the approximate result of point C in the plane rectangular coordinate system to obtain point C1; Step 3: Assume the distances from C1 to points A and B are L1 and L2. If both L1 and L2 are less than the preset distance, replace the great circle coordinate system with the rectangular coordinate system and use the coordinates of C1 as the coordinate position of point C; otherwise, proceed to the subsequent steps; Step 4, if both L1 and L2 are greater than the preset distance, it is determined that the distances from point C1 solved in the rectangular coordinate system to points A and B are shorter than the distances from the true position point C to points A and B. Respectively draw great circle paths starting from points A and B, θ 1. θ with azimuth angles of 2, draw great circle paths of a specified length, and obtain the end coordinates A1 and B1 of the two great circle paths; Step 5: Replace the original points A and B with the obtained A1 and B1, and repeat Steps 2 to 5 until both L1 and L2 are less than the preset distance, and output the final result.

7. The VLF emission source localization method based on three ground-based observation stations according to claim 6, wherein Step 2 includes: Step 21, according to the azimuth angle θ 1. Let the length of AC be r1, then the coordinates (x1, y1) of point C in the plane rectangular coordinate system are expressed as: ， Step 22. For the coordinates (x B , y B ) of point B, according to the azimuth θ 2 and assuming that the length of BC is r2, the coordinates (x2, y2) of point C are expressed as: ， Step 23, simultaneous equations , solve for r1 and r2; Step 24: After obtaining the coordinates of point C in the approximate plane rectangular coordinate system, convert them back to geographical coordinates. The conversion formula is as follows: If the coordinates of point C in the plane rectangular coordinate system are (x, y), then its latitude is , and its longitude is , where R is the radius of the earth.

8. The VLF emission source localization method based on three ground-based observation stations according to claim 6, wherein Step 3 includes: Step 31: Calculate the distances from C1 to points A and B according to the great circle distance formula. The formula is as follows: Assume to find A j (lat j , lon j ) and B k (lat k , lon k ) the distance between : wherein is an intermediate variable algebra, is a radian system function for obtaining longitude and latitude, and the specific function is as follows: Among them, is in radians, is in degrees. The frequency range of the very low frequency signal is 3 - 30 kHz, and the corresponding wavelength length is 10 - 100 km. If L1 and L2 are within the preset distance range, then under the current conditions, the rectangular coordinate system can replace the great circle coordinate system for calculation and solution, that is, the result calculated in Step 2 is the result within the error range. Under normal circumstances, L1 and L2 are much larger than the preset distance.

9. The very low frequency emission source localization method based on three ground-based observation stations according to claim 6, characterized in that Step 4 includes: Step 41: Draw two great circle paths with the lengths of L1 and L2. The longitude and latitude coordinates of their endpoints are calculated by the following formula: Taking the starting point A(lat1, lon1) and the azimuth angle θ1 as an example, the endpoint coordinates are A1(lat11, lon11) Among them, , , are the longitude and latitude of point A and the result of converting θ1 to radians, and R is the radius of the earth.

10. A very low frequency emission source positioning system based on three ground-based observation stations, characterized in that, Including: Deployment module, used to deploy a very low frequency signal emission source positioning system based on three ground-based observation stations; Startup module, used to start the very low frequency signal emission source positioning system to make each ground-based observation station enter the normal operation state; Verification module, used to determine the direction finding and receiving data of each ground-based observation station after all ground-based observation stations complete the verification of the direction finding results; Selection module, used to select effective observation station pairs according to the direction finding and receiving data and obtain the effective observation data of the effective observation station pairs; Positioning module, used to perform central intersection positioning evaluation using the effective observation data to determine the position information of the very low frequency emission source.

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