Method and system for locating a very low frequency emission source based on three ground-based observation stations

Abstract

The application provides a very low frequency signal source positioning method and system based on three ground-based observation stations, comprising: deploying a very low frequency signal source positioning system based on three ground-based observation stations; starting the very low frequency signal source positioning system, so that each ground-based observation station enters a normal operation state; after all ground-based observation stations complete direction finding result verification, determining the 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 using the effective observation data to perform central intersection positioning evaluation, and determining very low frequency signal source position information. The application uses multi-station cooperative positioning technology, can complete the monitoring and positioning of the very low frequency signal source in real time, efficiently and without monitoring blind area, has the advantages of simple calculation, rapid processing and high precision, and can be widely applied in the fields of electromagnetic signal detection, electromagnetic environment and earthquake precursor research.

Description

Technical Field

[0001] This invention relates to the field of very low frequency (VLF) detection and application technology, and in particular to a method and system for locating VLF transmitters based on three ground-based observation stations. Background Technology

[0002] Very Low Frequency (VLF) waves are electromagnetic waves with a frequency range of 3-30 kHz. They are characterized by long wavelengths and low propagation attenuation, with a typical attenuation coefficient of approximately 2-3 dB / Mm. VLF waves propagate over extremely long distances in Earth-ionospheric waveguides, making them valuable for applications in communications, space environment monitoring, and signal source localization. The propagation characteristics of VLF waves are closely related to the electron density of the D layer of the ionosphere. The D layer, located at an altitude of 60-100 km above the Earth's surface, is a partially ionized atmosphere with an electron density typically between 1-1000 cm⁻³. The D layer is affected by both top-down solar activity and bottom-up atmospheric fluctuations, causing its electron density to change dynamically and directly impacting the propagation performance of VLF waves.

[0003] VLF waves primarily originate from natural thunderstorms and artificial transmitting stations. Naturally occurring VLF waves are commonly used for signal detection of lightning activity, while artificial transmitting stations, with their stable signal transmission capabilities, are widely used in long-distance communication and space environment monitoring. Regardless of whether the VLF waves are from natural or artificial sources, their directional characteristics and time delay information provide an important foundation for high-precision signal source localization.

[0004] Current signal localization technologies are gradually evolving from single-point reference methods to multi-point collaborative direction finding. Traditional single-point methods, due to limited information, are easily affected by noise interference and environmental changes, resulting in insufficient positioning accuracy. In contrast, multi-point collaborative azimuth cross-location technology, by integrating directional data from multiple receivers and combining it with optimization algorithms, can significantly improve positioning accuracy and robustness. In signal source localization, this technology can effectively achieve efficient localization of dynamic signal sources by extracting the directional data of the target signal, providing a reliable solution for application needs in complex environments. Summary of the Invention

[0005] This invention provides a method and system for locating very low frequency (VLF) transmitters based on three ground-based observation stations, in order to overcome the deficiencies in the existing technology.

[0006] In a first aspect, the present invention provides a method for locating very low frequency (VLF) emission sources based on three ground-based observation stations, comprising:

[0007] Deploy a very low frequency signal transmission source localization system based on three ground-based observation stations;

[0008] The very low frequency signal transmitter positioning system is activated, enabling all local ground observation stations to enter normal operation.

[0009] After all ground-based observation stations have completed the verification of their orientation results, the orientation reception data of each ground-based observation station will be determined.

[0010] Select a valid pair of observation stations based on the direction finding data, and obtain the valid observation data of the valid pair of observation stations.

[0011] The effective observation data is used to perform center cross-location assessment to determine the location information of the very low frequency emission source.

[0012] According to the present invention, a method for locating very low frequency (VLF) transmitters based on three ground-based observation stations is provided, comprising deploying a VLF signal transmitter location system based on three ground-based observation stations, including:

[0013] The system consists of a first ground-based observation station, a second ground-based observation station, a third ground-based observation station, and a 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 with a 45-degree deflection, and the northwest-southeast direction with a 45-degree deflection, to receive very low frequency signals from different directions.

[0015] The very low frequency signal is acquired by the four-channel receiver, and amplitude and phase features are extracted.

[0016] The host computer performs directional analysis and direction finding evaluation on the specified frequency very low frequency signal and outputs the direction finding results.

[0017] The direction finding results are transmitted via the Internet in encrypted form to the central processing server for processing.

[0018] According to the present invention, a method for locating a very low frequency (VLF) transmitter based on three ground-based observation stations is provided, which involves activating the VLF signal transmitter location system to bring each ground-based observation station into normal operation, including:

[0019] After the very low frequency signal transmitter positioning system is activated, three ground-based observation stations will perform real-time direction finding of the very low frequency signal at the specified frequency.

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

[0021] According to the present invention, a method for locating a very low frequency (VLF) transmitter based on three ground-based observation stations includes selecting a valid pair of observation stations based on the direction-finding received data and obtaining valid observation data of the valid pair of observation stations, comprising:

[0022] Determine the first direction angle, second direction angle, and third direction angle corresponding to the 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 directional angle differences and select the two ground observation stations with the largest directional angle differences as the effective observation station pairs;

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

[0026] According to the present invention, a method for locating a very low frequency (VLF) transmitter based on three ground-based observation stations compares three directional angle differences and selects the two pairs of ground-based observation stations with the largest directional angle differences as the effective observation station pairs, including:

[0027] If the first directional angle difference is determined to be the maximum, then the first ground-based observation station and the second ground-based observation station are determined to be the effective observation station pair;

[0028] If the second directional angle difference is determined to be the maximum, then the first ground-based observation station and the third ground-based observation station are determined to be the effective observation station pair;

[0029] If the third directional angle difference is determined to be the maximum, then the second and third ground-based observation stations are determined to be the effective observation station pair.

[0030] According to the present invention, a method for locating a very low frequency (VLF) transmitter based on three ground-based observation stations is provided. This method utilizes the effective observation data to perform a center cross-location assessment to determine the VLF transmitter's location information, including:

[0031] Step 1: Determine the geographic coordinates of the first ground-based observation station as A(lat1,lon1), the geographic coordinates of the second ground-based observation station as B(lat2,lon2), and the geographic coordinates of the launch station location to be determined as C(lat3,lon3). Set the azimuth angles of point C relative to points A and B as θ1 and θ2.

[0032] Step 2: Solve for the approximate result of point C using a Cartesian coordinate system to obtain point C1;

[0033] Step 3: Let L1 and L2 be the distances from C1 to points A and B respectively. If both L1 and L2 are less than the preset distance, then replace the great circle coordinate system with the rectangular coordinate system and use the coordinates of C1 as the coordinates of point C. Otherwise, proceed to the next step.

[0034] Step 4: If L1 and L2 are both greater than the preset distance, then the distance from point C1 to points A and B calculated in the rectangular coordinate system is determined to be shorter than the distance from the actual point C to points A and B. Draw great circle paths with points A and B as the starting points and azimuth angles θ1 and θ2 as the azimuth angles. Draw great circle paths of a specified length and obtain the endpoint 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 the present invention, a method for locating a very low frequency (VLF) emission source based on three ground-based observation stations includes step 2 as follows:

[0037] Step 21, based on the azimuth angle θ1, let the length of AC be r1, then the coordinates (x1, y1) of point C in the Cartesian coordinate system are expressed as:

[0038] x1 = r1sinθ1, y1 = r1cosθ1

[0039] Step 22, for the coordinates of point B (x... B ,y B Based on 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 Solve for r1 and r2;

[0042] Step 24: After obtaining the coordinates of point C in the approximate Cartesian coordinate system, convert them back to geographic coordinates using the following formula:

[0043] Let the coordinates of point C in the Cartesian coordinate system be (x, y), then its latitude is... Longitude is Where R is the Earth's radius.

[0044] According to the present invention, a method for locating a very low frequency (VLF) emission source based on three ground-based observation stations includes step 3 as follows:

[0045] Step 31: Calculate the distance from C1 to points A and B using the great circle distance formula, as follows:

[0046] Suppose we need to find A j (lat j ,lon j ) and B k (lat k ,lon k Distance between )

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

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

[0049]

[0050] Where 'a' is an intermediate variable (algebraic), and 'Deg' is a radian function for calculating latitude and longitude, as shown below:

[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 signal has a frequency range of 3-30kHz, corresponding to a wavelength of 10-100km. 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. 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 the present invention, a method for locating a very low frequency (VLF) emission source based on three ground-based observation stations includes step 4:

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

[0056] Taking the starting point A(lat1,lon1) and azimuth angle θ1 as an example, the ending point 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 Earth's radius.

[0062] Secondly, the present invention also provides a very low frequency (VLF) transmitter location system based on three ground-based observation stations, comprising:

[0063] The deployment module is used to deploy a very low frequency signal transmitter location system based on three ground-based observation stations;

[0064] The startup module is used to start the very low frequency signal transmitter positioning system, so that the local ground observation stations can enter the normal operation state.

[0065] The verification module is used to determine the direction-finding data received by each ground-based observation station after all ground-based observation stations have completed the verification of their direction-finding results.

[0066] The selection module is used to select a valid pair of observation stations based on the direction finding received data, and to obtain the valid observation data of the valid pair of observation stations.

[0067] The positioning module is used to perform center cross-positioning assessment using the effective observation data to determine the location information of the very low frequency emission source.

[0068] This invention provides a method and system for locating very low frequency (VLF) transmitters based on three ground-based observation stations. By deploying multiple receiving stations to collect VLF wave directional data and utilizing cross-location algorithms and signal fusion processing technology, the location of the transmitter can be determined in real time under complex electromagnetic environments. Compared with traditional methods, this method significantly reduces positioning errors and improves the real-time performance and stability of the positioning system. This invention can be widely applied to high-precision positioning of signal sources, such as monitoring lightning signal sources during thunderstorms, precise positioning of artificial VLF transmitter stations, and source analysis of ionospheric disturbance signals. Through in-depth analysis of VLF signal characteristics and innovative optimization algorithms, this invention provides a completely new technical framework for VLF signal positioning technology, effectively meeting the needs of real-time positioning of dynamic targets and providing strong support for high-precision positioning engineering and related scientific research. Attached Figure Description

[0069] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

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

[0071] Figure 2 This is a structural diagram of the very low frequency signal transmission source positioning system based on three ground-based observation stations provided by the present invention;

[0072] Figure 3 This is the second flowchart of the very low frequency emission source localization method based on three ground-based observation stations provided by the present invention.

[0073] Figure 4 This is a schematic diagram of the very low frequency emission source positioning system based on three ground-based observation stations provided by the present invention;

[0074] Figure 5 This is a schematic diagram of the structure of the electronic device provided by the present invention. Detailed Implementation

[0075] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0076] Figure 1 This is one of the flowcharts illustrating the very low frequency (VLF) emission source localization method based on three ground-based observation stations provided in this embodiment of the invention, as shown below. Figure 1 As shown, it includes:

[0077] Step 100: Deploy a very low frequency signal transmission source localization system based on three ground-based observation stations;

[0078] Step 200: Activate the very low frequency signal transmission source positioning system to bring all local ground observation stations into normal operation.

[0079] Step 300: After all ground-based observation stations have completed the verification of their direction finding results, determine the direction finding data received by each ground-based observation station;

[0080] Step 400: Select a valid observation station pair based on the direction finding received data, and obtain the valid observation data of the valid observation station pair;

[0081] Step 500: Use the effective observation data to perform center cross-location assessment and determine the location information of the very low frequency emission source.

[0082] Specifically, the embodiments of the present invention employ the following... Figure 2 The illustrated Very Low Frequency (VLF) signal transmitter localization system, based on three ground-based observation stations, consists of three ground-based receiving stations (VLF Station 1, VLF Station 2, and VLF Station 3) and one central processing server. Each receiving station is equipped with four loop antennas, positioned in the north-south (NS), east-west (EW), and 45° deflected northeast-southwest (NE-SW) and northwest-southeast (NW-SE) directions, forming an omnidirectional receiving system for capturing VLF signals from different directions. Signals are acquired and amplitude and phase characteristics are extracted by a four-channel receiver. The host computer performs directional analysis and direction finding assessment on signals at specified frequencies. The direction finding results are transmitted encrypted to the central server via the internet. Based on the direction finding results from each receiving station, the central server selects the required signal pairs and runs a cross-location algorithm to comprehensively analyze the signal's directional information and accurately calculate the transmitter's location.

[0083] To meet the high-precision positioning requirements of very low frequency (VLF) signal transmitters, this invention proposes deployment requirements for three observation stations to ensure the system's direction-finding accuracy and positioning stability. First, the observation stations must be deployed in an equilateral triangle configuration, with the distance between stations reaching the order of kilometers. This geometric layout maximizes coverage of the target area and effectively reduces positioning errors by increasing the length of the geometric baseline for cross-positioning. Furthermore, the equilateral triangle layout ensures the complementarity of observation directions at each station, providing ideal geometric conditions for multi-point collaborative positioning.

[0084] Secondly, the observation station antennas must possess high directivity, with their directivity error controlled within a small range. Simultaneously, the polarity of all antennas must be consistent to ensure uniformity in the phase and direction information of the received signal. This precise antenna directivity and polarity consistency design is crucial for achieving high-precision direction finding and signal fusion processing, significantly improving the system's positioning accuracy and reliability, and exhibiting strong robustness, especially in complex electromagnetic environments.

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

[0086] The first step is system startup and data processing.

[0087] First, the positioning system is activated to ensure all observation stations are in normal operational status. After system startup, the three observation stations will perform real-time direction finding on a specified very low frequency (VLF) signal and transmit the results to the central server via an encrypted network. Each observation station needs to provide the following direction finding data: the azimuth angle of the target signal, a timestamp, and the station's latitude and longitude. The timestamp ensures that the direction finding results from the three observation stations correspond to the same signal event, thus guaranteeing data timeliness and consistency. Time synchronization can be achieved through high-precision time synchronization technology (such as GNSS time synchronization) to eliminate the impact of time differences between stations on positioning accuracy.

[0088] The second step is to receive and synchronize the direction finding data.

[0089] After verification, the direction-finding results from all observation stations are transmitted to the central server as the basis for subsequent cross-location algorithms. This process provides the positioning system with high-precision, synchronized directional information input, laying a solid foundation for the real-time and accurate positioning of the signal source.

[0090] The third step is to select effective observation stations.

[0091] (1) Calculate the direction angle difference

[0092] The direction angle (denoted as θ) from the three observation stations (A, B, and C) A θ B and θ C In the data, calculate the directional angular difference (denoted as Δθ) between each pair of stations. AB , Δθ AC and Δθ BC ), defined as:

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

[0094] The directional angle difference is limited to the range of [0°, 180°] to ensure the accuracy of the directional information.

[0095] (2) Select the group of stations with the largest directional angle difference.

[0096] Compare the angular differences in the three directions, and select the two observation pairs with the largest differences as the valid observation pairs, according to the following rules:

[0097] If Δθ AB If the maximum value is found, then sites A and B are selected.

[0098] If Δθ AC If the maximum value is reached, then sites A and C are selected;

[0099] If Δθ BC If the maximum value is found, then sites B and C are selected.

[0100] By selecting the station pair with the largest directional angle difference, the geometric stability of cross-positioning is ensured, avoiding a significant increase in positioning error due to collinearity, i.e., the geometric positions of the transmitter and the two receiving stations are close to a straight line.

[0101] (3) Record valid observation station data

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

[0103] The fourth step involves cross-location evaluation processing on the central server.

[0104] Step 1: Let the geographical coordinates of the two known receiving stations be A(lat1,lon1) and B(lat2,lon2), and let the location of the transmitting station be C(lat3,lon3); let the azimuth angles of point C relative to points A and B be θ1 and θ2.

[0105] Step 2: Solve for the approximate result using a Cartesian coordinate system. The result obtained in Step 2 is set as point C1.

[0106] Step 21: Based on the azimuth angle θ1, let the length of AC be r1. Then the coordinates (x1, y1) of point C in this Cartesian coordinate system can be expressed as:

[0107] x1 = r1sinθ1, y1 = r1cosθ1

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

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

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

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

[0112] Let the coordinates of point C in the Cartesian coordinate system be (x, y), then its latitude... longitude (where R is the Earth's radius).

[0113] Step 3: Based on the results calculated in Step 2, make a judgment. Let the distances from C1 to points A and B be L1 and L2, respectively. Condition 1: Both L1 and L2 are less than 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 coordinates of point C. Condition 2: If condition 1 is not met, proceed to the next step.

[0114] Step 31: Calculate the distance from C1 to points A and B using the great circle distance formula. The formula is as follows: Assume we are calculating the distance from A... j (lat j ,lon j ) and B k (lat k ,lon k Distance 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 an intermediate variable (algebraic), and 'Deg' is a radian function for calculating latitude and longitude, as shown below:

[0119] lat_rad=lat×π / 180

[0120] Where lat_rad is in radians and lat is in degrees;

[0121] Step 32: The very low frequency signal has a frequency range of 3-30kHz and a wavelength of 10-100km. If L1 and L2 are within 1km, then under the current conditions, the rectangular coordinate system can be used instead of 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 >> 1km.

[0122] Step 4: When L1 and L2 > 1km, we know that the distance from point C1 to points A and B calculated using the rectangular coordinate system is shorter than the actual distance from point C to points A and B. Draw great circle paths with points A and B as the starting points and azimuth angles θ1 and θ2 as the azimuth angles, respectively. Draw great circle paths of a specified length to obtain the endpoint coordinates A1 and B1 of the two great circle paths.

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

[0124]

[0125] 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 Earth's radius.

[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 condition 1 of step 3 is met, that is, output the final position C1 as the result.

[0127] The method flow of the present invention is illustrated below with an example, including:

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

[0129] Step 11: Let A and B be two known receiving stations, with corresponding geographic coordinates A(lat1,lon1) and B(lat2,lon2). Let C(lat3,lon3) be the location of the transmitting station to be obtained. Let θ1 and θ2 be the azimuth angles of point C relative to points A and B. Given the coordinates of A and B, and the values ​​of θ1 and θ2, solve for the coordinate position of point C.

[0130] Step 2: Solve for the approximate result using a Cartesian coordinate system. The result obtained in Step 2 is set as point C1.

[0131] Step 3: Based on the results calculated in Step 2, make a judgment. Let the distances from C1 to points A and B be L1 and L2, respectively. Condition 1: Both L1 and L2 are less than 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 coordinates of point C. Condition 2: If condition 1 is not met, proceed to the next step.

[0132] Step 32: The very low frequency signal has a frequency range of 3-30kHz and a wavelength of 10-100km. If L1 and L2 are within 1km, then under the current conditions, the rectangular coordinate system can be used instead of 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 >> 1km.

[0133] Step 4: When L1 and L2 > 1km, we know that the distance from point C1 to points A and B calculated using the rectangular coordinate system is shorter than the actual distance from point C to points A and B. Draw great circle paths with points A and B as the starting points and azimuth angles θ1 and θ2 as the azimuth angles, respectively. Draw great circle paths of a specified length to obtain the endpoint 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 condition 1 of step 3 is satisfied, i.e., output the final result; Verification example:

[0135] Specifically, in this embodiment of the invention, the receiving station located at DC (29.3543, 100.1435) is used as station A, the receiving station located at SZ (31.5657, 113.3181) is used as station B, and three very low frequency transmitting stations that need to be calculated, NWC (-21.8, 114.15), JJI (32.4, 130.49) and VTX (8.2, 77.46), are used as the C-point transmitting stations that need to be solved.

[0136] The coordinates of the three launch stations calculated using the method of this invention are (-21.79994, 114.14998), with an error of 6.984m; (32.400005, 130.49007), with an error of 6.595m; and (8.20002, 77.46003), with an error of 3.98m. The calculation times are 9.64s, 9.63s, and 9.62s, respectively, demonstrating the feasibility of this method.

[0137] This invention provides a transmitter source localization system and method based on three ground-based very low frequency (VLF) observation stations, aiming to accurately locate transmitter sources using a high-precision localization algorithm. The system consists of three observation stations deployed in an equilateral triangle with large spacing and a central processing server. It can acquire VLF signals with high precision and perform direction finding assessments on signals of specified frequencies via a host computer. The measurement results are transmitted encrypted over the Internet to the central server for processing. The central server uses the received angle information and receiver station location data to accurately calculate the geographical location of the transmitter source using a cross-localization algorithm. This method first solves for preliminary localization results using a Cartesian coordinate system, and then performs multiple iterations of optimization using a great circle path segmentation method, ultimately outputting a localization result that meets the accuracy requirements. Compared with traditional methods, this invention features a simple and efficient calculation process and high positioning accuracy. Through multiple observation stations and a precise localization algorithm, this invention significantly improves the accuracy of VLF signal source localization and effectively reduces positioning errors, making it suitable for electromagnetic environment monitoring, signal source localization, and VLF signal detection. This system is particularly suitable for military reconnaissance, marine exploration, and electromagnetic environment monitoring scenarios, possessing significant military and civilian value. The system requires three ground observation stations arranged in an equilateral triangle pattern with a large distance between them to ensure high-precision signal source location. Measurement results need to be transmitted via the internet, thus requiring a stable network environment. Although the system has strong environmental adaptability, appropriate calibration and optimization are still necessary in environments with high electromagnetic interference to ensure accurate signal reception. This invention is significant in improving electromagnetic monitoring accuracy and promoting the application of VLF signal technology. It can also provide technical support in multiple fields such as military, security, and resource exploration, promoting the progress and development of related industries.

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

[0139] Figure 4 This is a schematic diagram of the structure of a very low frequency (VLF) transmitter location system based on three ground-based observation stations provided in an embodiment of the present invention, as shown below. Figure 4 As shown, it includes: deployment module 91, startup module 92, verification module 93, selection module 94, and positioning module 95, wherein:

[0140] The deployment module 91 is used to deploy a very low frequency (VLF) signal transmitter location system based on three ground-based observation stations; the startup module 92 is used to start the VLF signal transmitter location system, enabling each ground-based observation station to enter normal operation; 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 have completed the direction-finding result verification; the selection module 94 is used to select valid observation station pairs based on 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 center cross-positioning evaluation using the valid observation data to determine the VLF transmitter location information.

[0141] Figure 5 An example is a schematic diagram of the physical structure of an electronic device, such as... Figure 5 As shown, the electronic device may include a processor 1010, a communications interface 1020, a memory 1030, and a communication bus 1040. The processor 1010, communications interface 1020, and memory 1030 communicate with each other via the communication bus 1040. The processor 1010 can call logical instructions in the memory 1030 to execute a very low frequency (VLF) transmitter location method based on three ground-based observation stations. This method includes: deploying a VLF signal transmitter location system based on three ground-based observation stations; activating the VLF signal transmitter location system to bring each ground-based observation station into normal operation; determining the direction-finding reception data of each ground-based observation station after all ground-based observation stations have completed direction-finding result verification; selecting effective observation station pairs based on the direction-finding reception data and acquiring effective observation data for the effective observation station pairs; and using the effective observation data to perform a center cross-location assessment to determine the VLF transmitter location information.

[0142] Furthermore, the logical instructions in the aforementioned memory 1030 can be implemented as software functional units and, when sold or used as independent products, can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or a part of the 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 to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

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

[0144] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus necessary general-purpose hardware platforms, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solutions, 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 disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in the 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 not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for locating a very low frequency transmitting source based on three ground-based observation stations, characterized in that, The method comprises the following steps: deploying a very low frequency signal source positioning system based on three ground observation stations; starting the very low frequency signal source positioning system to make each ground observation station enter a normal operation state; after all the ground observation stations complete the verification of the direction finding results, determining the direction finding receiving data of each ground 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; using the effective observation data to perform central intersection positioning evaluation to determine the very low frequency signal source position information, comprising: Step 1, determine the geographic coordinates of the first ground observation station as A (lat1, lon1), and the geographic coordinates of the second ground observation station as B (lat2, lon2), the geographic coordinates of the to-be-determined transmitting station position as C (lat3, lon3), and the azimuth of the C point relative to the A and B points is set as θ 1 and θ 2; Step 2: obtaining the C1 point by solving the C point approximate result through a plane rectangular coordinate system; Step 3: setting the distances between C1 and A and B as L1 and L2, if L1 and L2 are both less than a preset distance, replacing the great circle coordinate system with a rectangular coordinate system and taking the C1 coordinate as the coordinate position of the C point, otherwise, performing the subsequent steps; Step 4, if L1 and L2 are both greater than the preset distance, it is determined that the distance from the C1 point solved in the rectangular coordinate system to the A and B points is shorter than the distance from the real point C to the A and B points, and the A and B points are respectively taken as the starting points, θ 1、 θ 2 is the great circle path of the azimuth angle, the great circle path of the specified length is drawn, and the end point coordinates A1 and B1 of the two great circle paths are obtained; Step 5: replacing the original A and B points with A1 and B1 obtained, repeating steps 2 to 5 until L1 and L2 are both less than the preset distance, and outputting the final result.

2. The three ground-based observation station based very low frequency transmitter source positioning method according to claim 1, characterized in that, Deploying a very low frequency signal source positioning system based on three ground observation stations, comprising: a first ground observation station, a second ground observation station, a third ground observation station and a central processing server, each ground observation station comprising four ring antennas, a four-channel receiver and an upper computer; the four ring antennas are arranged in the north-south direction, the east-west direction, the northeast-southwest direction with a deflection of 45 degrees and the northwest-southeast direction with a deflection of 45 degrees, and are used for receiving very low frequency signals in different directions; the four-channel receiver is used for collecting the very low frequency signals and extracting amplitude characteristics and phase characteristics; the upper computer is used for performing directivity analysis and direction finding evaluation on the specified frequency very low frequency signals and outputting direction finding results; the direction finding results are transmitted to the central processing server through the Internet for processing.

3. The three ground-based observation station based very low frequency transmitter source positioning method of claim 1, wherein, Starting the very low frequency signal source positioning system to make each ground observation station enter a normal operation state, comprising: after the very low frequency signal source positioning system is started, the three ground observation stations perform real-time direction finding on the specified frequency very low frequency signals; each ground observation station outputs the direction angle, time stamp and latitude and longitude position information of the target signal.

4. The three ground-based observation station based very low frequency transmitter source positioning method of claim 1, wherein, Selecting an effective observation station pair according to the direction finding receiving data and obtaining effective observation data of the effective observation station pair, comprising: determining a first direction angle, a second direction angle and a third direction angle corresponding to the three ground observation stations respectively; calculating a first direction angle difference between the first direction angle and the second direction angle, a second direction angle difference between the first direction angle and the third direction angle, and a third direction angle difference between the second direction angle and the third direction angle, all the direction angle differences being in the range of 0 degrees to 180 degrees; comparing the three direction angle differences, selecting two groups of ground observation stations with the largest direction angle difference value as the effective observation station pair; obtaining the latitude and longitude coordinates and direction angle data of the effective observation station pair, discarding the direction finding result of the third station, and re-determining the effective observation station pair as a new first ground observation station and a new second ground observation station.

5. The three ground-based observation station based very low frequency transmitter source positioning method of claim 4, wherein, Comparing the three direction angle differences, select the two groups of foundation observation stations with the largest direction angle difference value as the effective observation station pair, including: If it is determined that the first direction angle difference is the largest, the first foundation observation station and the second foundation observation station are determined as the effective observation station pair; If it is determined that the second direction angle difference is the largest, the first foundation observation station and the third foundation observation station are determined as the effective observation station pair; If it is determined that the third direction angle difference is the largest, the second foundation observation station and the third foundation observation station are determined as the effective observation station pair.

6. The three ground-based observation station based very low frequency transmitter source positioning method of claim 1, 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 represented as: ， Step 22, for the B point coordinates (x B , y B ), according to the azimuth angle θ 2 and assuming the length of BC is r2, the point C coordinates (x2, y2) are expressed as: ， Step 23, solve the equations for r1 and r2. Step 24, after obtaining the coordinates of point C in the approximate plane rectangular coordinate system, convert it back to geographic coordinates, and the conversion formula is as follows: Let the coordinates of point C in the plane rectangular coordinate system be (x, y), then the latitude of C is and the longitude of C is where R is the radius of the earth.

7. The three ground-based observation station based very low frequency transmitter source positioning method of claim 1, wherein, Step 3 includes: Step 31, according to the great circle distance formula, calculate the distance between C1 and points A and B, and the formula is as follows: Assume that the distance between A j (lat j , lon j ) and B k (lat k , lon k ) is calculated : where is an intermediate variable algebra, is a radian function for calculating latitude and longitude, and the specific function is as follows: wherein is in radians, is in degrees; Step 32, the frequency range of very low frequency signal is 3-30 kHz, corresponding to the 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 replaces the great circle coordinate system for operation 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.

8. The three ground-based observation station based very low frequency transmitter source positioning method of claim 1, wherein, Step 4 includes: Step 41, draw two great circle paths with the lengths of L1 and L2, and the longitude and latitude coordinates of the endpoints are calculated by the following formula: Take the starting point A (lat1, lon1) and the azimuth angle θ1 as an example, and the terminal coordinates are A1 wherein , , are the latitude and longitude of point A and θ1 is the result of converting the angle to radians, and R is the radius of the earth.

9. A three ground-based observation station based very low frequency emission source positioning system based on the three ground-based observation station based very low frequency emission source positioning method according to any one of claims 1 to 8, characterized in that, Including: The deployment module is used to deploy a very low frequency signal source positioning system based on three ground-based observation stations; The starting module is used to start the very low frequency signal source positioning system, so that each ground-based observation station enters a normal operating state; The verification module is used to determine the direction finding receiving data of each ground-based observation station after all ground-based observation stations complete the direction finding result verification; The selection module is used to select an effective observation station pair according to the direction finding receiving data, and obtain effective observation data of the effective observation station pair; The positioning module is used to perform central intersection positioning evaluation using the effective observation data, and determine the very low frequency signal source position information.

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