A ground-based multi-channel very low frequency signal direction finding method and system

Abstract

The present invention provides a ground-based multi-channel very low frequency (VLF) signal direction-finding method and system, comprising: deploying a four-channel VLF signal direction-finding system to obtain four-channel broadband VLF signal sampling data; calculating the signal-to-noise ratio corresponding to the four-channel broadband VLF signal sampling data, and using a station direction-finding algorithm to determine the effective antenna pair in the four-channel VLF signal direction-finding system based on the signal-to-noise ratio; using the amplitude comparison direction-finding method to calculate the signal azimuth using the effective antenna pair, determining the quadrant of the signal direction based on the signal azimuth, and outputting the final signal azimuth; performing angle compensation on the final signal azimuth, and outputting the actual azimuth of the measured signal. By deploying a four-channel VLF signal direction-finding system, the present invention can conveniently and effectively achieve real-time determination of the VLF signal's incoming direction, and has the advantages of simple structure, high computational efficiency, and the ability to address VLF direction-finding blind spots.

Description

Technical Field

[0001] The present invention relates to the technical field of very low frequency fluctuation detection, and in particular to a ground-based multi-channel very low frequency signal direction finding method and system. Background Art

[0002] Very Low Frequency (VLF) waves mainly refer to a type of wave with a frequency of 3 kHz-30 kHz. The wavelength of this type of wave is in the range of 100 km-10 km. It has the characteristics of low propagation loss, high skin depth, and long propagation distance. It can achieve long-distance propagation in the Earth-ionosphere waveguide composed of the Earth's surface (seawater, land) and the lower ionosphere. There are two main sources of very low frequency electromagnetic waves: (1) natural very low frequency electromagnetic waves radiated by lightning pulses. Lightning is divided into cloud flashes, ground flashes, etc., and when it occurs, it will generate a lot of energy, which can be seen by the naked eye, such as visible light; the electromagnetic wave frequency range is from a few Hz to hundreds of MHz. (2) very low frequency electromagnetic waves for communication purposes radiated by artificial stations. When very low frequency electromagnetic waves propagate in the Earth-ionosphere waveguide, their attenuation rate is usually very low, with an attenuation level of ~2-3 dB / 1000 km, and they can propagate very long distances. A large number of artificial very low frequency stations have been established by various countries around the world. They are mainly used for submarine communications, marine navigation and precise timing. According to public information, they mainly operate in the frequency band of 10kHz-50kHz, and there are also many unpublished artificial station signals in between.

[0003] Locating very low frequency (VLF) transmitters through technical means has important applications in VLF signal monitoring. Direction-finding systems are categorized into scalar and vector direction-finding systems, depending on how the antenna system extracts and processes information from incoming signals. Scalar direction-finding systems are older and more widely used, producing a figure-eight directional pattern for vertically polarized waves. Vector direction-finding systems, on the other hand, are capable of extracting and utilizing vector information from incoming signals. Data acquisition in vector systems requires the use of a multi-port antenna array and at least two receivers with identical phase and amplitude at the front end, while a computer performs the data acquisition based on an algorithm at the back end. As radio waves travel, the direction-finding antenna uses the characteristic of receiving incoming waves of varying amplitudes from different directions to determine the incoming wave's direction. If the antennas are orthogonal, this method evolves into the classic Watson-Watt direction-finding method, also known as amplitude-comparison direction-finding. However, in practice, in addition to antenna setup accuracy and channel consistency, which can lead to deviations in direction-finding results, many other factors, such as the polarization state of the wave, the state of the ionosphere, and environmental interference, can also contribute to a degree of error, requiring targeted solutions. A single set of orthogonal antennas will bring about the problem of direction-finding blind spots. That is, when the antenna is nearly parallel to the direction of the target signal, the energy of the very low frequency signal received by the channel is minimal (even close to 0), becoming unusable, and therefore unable to effectively complete the direction determination of the signal. Summary of the Invention

[0004] The present invention provides a ground-based multi-channel very low frequency signal direction finding method and system, which are used to solve the defects of inaccurate very low frequency direction finding and many blind areas in the prior art.

[0005] In a first aspect, the present invention provides a ground-based multi-channel very low frequency signal direction finding method, comprising:

[0006] Deploy a four-channel very low frequency signal direction finding system to obtain four-channel broadband very low frequency signal sampling data;

[0007] calculating a signal-to-noise ratio corresponding to the four-channel broadband very low frequency signal sampling data, and determining an effective antenna pair in the four-channel very low frequency signal direction finding system using a station direction finding algorithm based on the signal-to-noise ratio;

[0008] Adopting the amplitude comparison direction finding method, using the effective antenna pair to calculate the signal azimuth, determining the quadrant in which the signal direction is located according to the signal azimuth, and outputting the final signal azimuth;

[0009] Angle compensation is performed on the final signal azimuth, and the actual azimuth of the measurement signal is output.

[0010] According to a ground-based multi-channel very low frequency signal direction finding method provided by the present invention, a four-channel very low frequency signal direction finding system is deployed, comprising:

[0011] Determining that the first group of antennas includes two orthogonal antennas in the north-south direction and the east-west direction, respectively receiving the north-south component of the station signal and the east-west component of the station signal, and converting the north-south component of the station signal and the east-west component of the station signal into the amplitude of the north-south magnetic field component of the station signal and the amplitude of the east-west magnetic field component of the station signal;

[0012] Calculating the signal northing angle based on the north-south component of the station signal and the east-west component of the station signal, or based on the amplitude of the north-south magnetic field component of the station signal and the amplitude of the east-west magnetic field component of the station signal;

[0013] Determining that the second antenna group includes two orthogonal antennas, which are tilted at a 45-degree clockwise angle with the two orthogonal antennas in the first antenna group, respectively receive the north-south deflection component and the east-west deflection component of the station signal, and convert the north-south deflection component and the east-west deflection component of the station signal into the amplitude of the north-south deflection magnetic field component and the amplitude of the east-west deflection magnetic field component of the station signal;

[0014] The north deflection angle of the signal is calculated based on the north-south deflection component of the station signal and the east-west deflection component of the station signal, or based on the amplitude of the north-south deflection magnetic field component of the station signal and the amplitude of the east-west deflection magnetic field component of the station signal.

[0015] According to a ground-based multi-channel very low frequency signal direction finding method provided by the present invention, calculating the signal-to-noise ratio corresponding to the four-channel broadband very low frequency signal sampling data includes:

[0016] Performing fast Fourier transform on the north-south component of the station signal, the east-west component of the station signal, the north-south deflection component of the station signal, and the east-west deflection component of the station signal, and then calculating the power spectral density to obtain the power spectral density corresponding to each component;

[0017] Obtaining a center frequency and a signal bandwidth of a very low frequency station signal, and determining a given noise bandwidth, wherein the noise bandwidth is greater than the signal bandwidth;

[0018] A first frequency range is obtained by taking the center frequency as the midpoint and half of the signal bandwidth, and a second frequency range is obtained by taking the center frequency as the midpoint and half of the noise bandwidth;

[0019] Calculating the mean of the power spectral density corresponding to each component within the first frequency range to obtain the first signal strength of each component, and calculating the mean of the power spectral density corresponding to each component within the second frequency range to obtain the second signal strength of each component;

[0020] The second signal strength of each component is subtracted from the first signal strength of each component to obtain the north-south component signal-to-noise ratio, the east-west component signal-to-noise ratio, the north-south deflection component signal-to-noise ratio, and the east-west deflection component signal-to-noise ratio.

[0021] According to a ground-based multi-channel very low frequency signal direction finding method provided by the present invention, based on the signal-to-noise ratio, a station direction finding algorithm is used to determine the effective antenna pair in the four-channel very low frequency signal direction finding system, comprising:

[0022] Determine the minimum signal-to-noise ratio threshold;

[0023] If it is determined that the north-south component signal-to-noise ratio and the east-west component signal-to-noise ratio are both greater than the minimum signal-to-noise ratio threshold, and the north-south deflection component signal-to-noise ratio and the east-west deflection component signal-to-noise ratio do not simultaneously meet the requirement of being greater than the minimum signal-to-noise ratio threshold, then using the sampled data of the first group of antennas;

[0024] If it is determined that the signal-to-noise ratio of the north-south deflection component and the signal-to-noise ratio of the east-west deflection component are both greater than the minimum signal-to-noise ratio threshold, and the signal-to-noise ratio of the north-south component and the signal-to-noise ratio of the east-west component do not simultaneously meet the requirement of being greater than the minimum signal-to-noise ratio threshold, then using the sampling data of the second group of antennas;

[0025] If it is determined that the north-south component signal-to-noise ratio, the east-west component signal-to-noise ratio, the north-south deflection component signal-to-noise ratio, and the east-west deflection component signal-to-noise ratio are all greater than the minimum signal-to-noise ratio threshold, then when the sum of the north-south component signal-to-noise ratio and the east-west component signal-to-noise ratio is greater than the sum of the north-south deflection component signal-to-noise ratio and the east-west deflection component signal-to-noise ratio, the sampling data of the first group of antennas is used; otherwise, the sampling data of the second group of antennas is used;

[0026] If it is determined that the north-south component signal-to-noise ratio and the east-west component signal-to-noise ratio do not simultaneously satisfy the minimum signal-to-noise ratio threshold, and the north-south deflection component signal-to-noise ratio and the east-west deflection component signal-to-noise ratio do not simultaneously satisfy the minimum signal-to-noise ratio threshold, no antenna data is used and the execution of the station direction finding algorithm is terminated.

[0027] According to the present invention, a ground-based multi-channel very low frequency signal direction finding method is provided, which adopts the amplitude comparison direction finding method and uses the effective antenna pair to calculate the signal azimuth, including:

[0028] If the effective antenna is the first antenna group, the north-south antenna is determined to be the first antenna, and the east-west antenna is determined to be the second antenna; if the effective antenna is the second antenna group, the north-south deflection antenna is determined to be the first antenna, and the east-west deflection antenna is determined to be the second antenna;

[0029] Acquire a first original sampled signal from the first antenna and a second original sampled signal from the second antenna;

[0030] Performing mixing based on the center frequency, and performing IQ demodulation on the first original sampling signal and the second original sampling signal respectively to obtain a first sampled I component mixing signal, a first sampled Q component mixing signal, a second sampled I component mixing signal, and a second sampled Q component mixing signal;

[0031] Determining an upper cutoff frequency of a low-pass filter according to the signal bandwidth, and performing low-pass filtering using the upper cutoff frequency to obtain a first sampled I component filtered signal, a first sampled Q component filtered signal, a second sampled I component filtered signal, and a second sampled Q component filtered signal;

[0032] Calculate the first antenna station signal amplitude based on the first sampled I component filtered signal and the first sampled Q component filtered signal, and calculate the second antenna station signal amplitude based on the second sampled I component filtered signal and the second sampled Q component filtered signal;

[0033] The signal azimuth is obtained according to the signal amplitude of the first antenna station and the signal amplitude of the second antenna station.

[0034] According to a ground-based multi-channel very low frequency signal direction finding method provided by the present invention, the quadrant in which the signal direction is located is determined according to the signal azimuth, and the final signal azimuth is output, comprising:

[0035] A Cartesian coordinate system is constructed using the two orthogonal antenna directions of the selected antenna group as coordinate axes. If the first antenna group is selected, the x-axis is the east-west component direction, with the due east direction being the positive x-axis direction, and the y-axis is the north-south component direction, with the due north direction being the positive y-axis direction. If the second antenna group is selected, the x-axis is the east-west deflection component direction, with the southeast direction being the positive x-axis direction, and the y-axis is the north-south deflection component direction, with the northeast direction being the positive y-axis direction. The first, second, third, and fourth quadrants are determined in sequence by rotating counterclockwise from the positive x-axis of the Cartesian coordinate system.

[0036] performing narrow-band filtering on the first antenna sampling signal and the second antenna sampling signal at the center frequency to obtain a first very low frequency station signal and a second very low frequency station signal, and calculating a carrier correlation coefficient between the first very low frequency station signal and the second very low frequency station signal;

[0037] If it is determined that the carrier correlation coefficient is greater than 0, it is determined that the direction of the very low frequency station signal is located in the first quadrant or the third quadrant; otherwise, it is determined that the direction of the very low frequency station signal is located in the second quadrant or the fourth quadrant;

[0038] If the very low frequency station signal is located in the first quadrant or the third quadrant, the final signal azimuth of the very low frequency station signal is corrected to the signal azimuth; if it is determined that the very low frequency station signal is located in the second quadrant or the fourth quadrant, the final signal azimuth of the very low frequency station signal is corrected to the negative angle corresponding to the signal azimuth.

[0039] According to a ground-based multi-channel very low frequency signal direction finding method provided by the present invention, angle compensation is performed on the final signal azimuth angle, and the actual azimuth angle of the measured signal is output, comprising:

[0040] If the first group of antennas is used to execute the station direction finding algorithm, determining the actual azimuth of the measured signal to be the final signal azimuth;

[0041] If the second group of antennas is used to execute the station direction finding algorithm, the actual azimuth of the measured signal is determined to be the final signal azimuth plus 45 degrees.

[0042] In a second aspect, the present invention further provides a ground-based multi-channel very low frequency signal direction finding system, comprising:

[0043] A deployment module is used to deploy a four-channel very low frequency signal direction finding system and obtain four-channel broadband very low frequency signal sampling data;

[0044] a calculation module, configured to calculate a signal-to-noise ratio corresponding to the four-channel broadband very low frequency signal sampling data, and determine an effective antenna pair in the four-channel very low frequency signal direction finding system using a station direction finding algorithm based on the signal-to-noise ratio;

[0045] a comparison module, configured to adopt an amplitude comparison direction finding method, use the effective antenna pair to calculate the signal azimuth, determine the quadrant in which the signal direction is located according to the signal azimuth, and output a final signal azimuth;

[0046] The compensation module is used to perform angle compensation on the final signal azimuth and output the actual azimuth of the measured signal.

[0047] In a third aspect, the present invention further provides an electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the program, the ground-based multi-channel very low frequency signal direction finding method as described in any one of the above-mentioned methods is implemented.

[0048] In a fourth aspect, the present invention further provides a non-transitory computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements any of the above-described ground-based multi-channel very low frequency signal direction finding methods.

[0049] The ground-based multi-channel very low frequency (VLF) signal direction-finding method and system provided by the present invention can conveniently and effectively realize real-time determination of the direction of VLF signals by deploying a four-channel VLF signal direction-finding system. It has the advantages of simple structure, high computational efficiency, and the ability to resolve VLF direction-finding blind spots. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0051] Figure 1 This is one of the flow charts of the ground-based multi-channel very low frequency signal direction finding method provided by the present invention;

[0052] Figure 2 This is the second flow chart of the ground-based multi-channel very low frequency signal direction finding method provided by the present invention;

[0053] Figure 3 This is a schematic diagram of the antenna installation of the multi-channel very low frequency direction finding system provided by the present invention;

[0054] Figure 4 This is a schematic diagram of the composition of the multi-channel very low frequency signal direction finding system provided by the present invention;

[0055] Figure 5 This is an example diagram of the multi-channel very low frequency direction finding results provided by the present invention;

[0056] Figure 6 It is a structural diagram of the ground-based multi-channel very low frequency signal direction finding system provided by the present invention;

[0057] Figure 7 It is a structural schematic diagram of the electronic device provided by the present invention. DETAILED DESCRIPTION

[0058] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0059] In response to the problems existing in the prior art, the present invention designs a ground-based multi-channel very low frequency signal direction-finding system based on a deep understanding of very low frequency signal propagation and the accumulated research on very low frequency signal detection and application. It mainly solves the problem of very low frequency direction-finding blind spots. The method used can simply and effectively complete the direction determination of very low frequency signals.

[0060] Figure 1 This is one of the flow charts of the ground-based multi-channel very low frequency signal direction finding method provided by an embodiment of the present invention, such as Figure 1 As shown, including:

[0061] Step 100: deploying a four-channel very low frequency signal direction finding system to obtain four-channel broadband very low frequency signal sampling data;

[0062] Step 200: Calculate the signal-to-noise ratio corresponding to the four-channel broadband very low frequency signal sampling data, and determine the effective antenna pair in the four-channel very low frequency signal direction finding system using a station direction finding algorithm based on the signal-to-noise ratio;

[0063] Step 300: using the amplitude comparison direction finding method, using the effective antenna pair to calculate the signal azimuth, determining the quadrant of the signal direction according to the signal azimuth, and outputting the final signal azimuth;

[0064] Step 400: Perform angle compensation on the final signal azimuth angle and output the actual azimuth angle of the measured signal.

[0065] Specifically, if Figure 2As shown in the flowchart, the present invention first deploys a four-channel very low frequency detection device, runs the monitoring system in the device to collect signals, collects the station signals of the corresponding antenna group, processes the signals of a given frequency, determines the antenna pair that is effective for direction finding, and after determining the effective antenna pair, further calculates the azimuth of the signal and eliminates the 90-degree phase ambiguity. Finally, the corresponding azimuth is compensated and the true direction of the measured signal is output.

[0066] The first step is to deploy four-channel very low frequency detection equipment

[0067] The antenna layout of the VLF signal direction finding system is set. The VLF amplitude-to-direction finding receives the incoming signal through two orthogonal antennas, the north-south (NS) and the east-west (EW), at the receiving station. The north-south component of the station signal is obtained respectively ( ) and the weight of things ( ), the angle between the direction of the signal and the north direction can be obtained according to the following formula, that is, the north deflection angle .

[0068] (1)

[0069] The amplitude of the magnetic field component in the corresponding direction of the signal is used , , the above formula is converted to:

[0070] (2)

[0071] When the VLF signal is parallel to the direction of a certain antenna, the signal strength of the station received by the antenna in this direction will drop sharply or even be drowned in the background noise, resulting in a direction finding blind spot. To solve this problem, this system adds a set of orthogonal antennas at a 45° angle to the original antenna. When the signal strength of one set of antennas is too low, the data of the other set of antennas is used for direction finding. The antenna system layout is as follows: Figure 3 shown.

[0072] Since the direction of the antenna changes, the direction finding calculation formula is transformed into:

[0073] (3)

[0074] It is the angle between the VLF signal direction and the north-south (NS_45) antenna direction after deflection by 45°. Therefore, there is a 45° difference between the calculated direction angle and the actual signal direction. Finally, the direction determination result of the VLF signal is obtained by compensating for 45°.

[0075] Furthermore, the very low frequency signal direction-finding system in the present invention is mainly composed of four inductive magnetic antennas, a four-channel very low frequency signal receiver and a control computer. The four antennas are set up in the set direction, and the corresponding receiver channels collect the target signal in real time. The control computer then processes the data and calculates the source direction of the target signal. Two mutually orthogonal antennas constitute an antenna system Antenna I, which are respectively set up in the east-west (EW) and north-south (NS) directions; the other two mutually orthogonal antennas constitute the second antenna system Antenna II, which is deflected 45° clockwise as a whole, that is, the antenna setting direction is 45° to the north-south (NS) direction, and are marked as EW_45 and NS_45 respectively. The very low frequency signal direction-finding system is composed of the following: Figure 4 shown.

[0076] The second step is to implement the very low frequency signal direction finding method based on the completion of the deployment of four-channel very low frequency detection equipment.

[0077] (1) Deploy a very low frequency (VLF) signal direction-finding system to ensure that the antenna installation directivity accuracy meets the requirement of better than 0.1° and ensure the consistency of the receiver channels. Turn on the system and enter the normal data acquisition mode to obtain four-channel broadband VLF signal sampling data.

[0078] (2) For a given center frequency Sum signal bandwidth The VLF station signal is processed, and the signal-to-noise ratio (SNR) of the four signals is calculated. NS , SNR EW， SNR NS_45 , SNR EW_45 .

[0079] The specific calculation method of the signal-to-noise ratio (SNR) of each signal is as follows: First, perform fast Fourier transform (FFT) on the broadband very low frequency data to obtain the spectrum , and then calculate the power spectral density PSD according to formula (4), unit dB

[0080] (4)

[0081] At the center frequency Nearby, frequency range Calculate the mean of the power spectrum density as the signal strength ;For a given noise bandwidth (Should meet ), in the frequency range and Calculate the mean of the power spectral density as the noise intensity Calculate the signal-to-noise ratio according to formula (5):

[0082] (5)

[0083] (3) Set the minimum threshold of signal-to-noise ratio 10dB ( Adjustments can be made based on the electromagnetic environment). The signal-to-noise ratios of the two orthogonal antenna groups are compared. If the signal-to-noise ratio of the first antenna group is better, the station direction-finding algorithm is executed using the sampled data of the first antenna group. Otherwise, the station direction-finding algorithm is executed using the sampled data of the second antenna group. The criteria for determining the better antenna group are as follows:

[0084] I. If and ,and and Not greater than , then the sampling data of the first group of antennas is selected;

[0085] II. If and ,and and Not greater than , then the sampling data of the second group of antennas is selected;

[0086] III. If 、 、 and At the same time, satisfying greater than , then according to and The antenna group is selected based on the comparison result of the size of Greater than When the first antenna is selected, Less than When , select the second set of antennas;

[0087] IV. If and Not greater than ,and and Nor is it greater than When , it is considered that the signal quality of both antenna groups is poor, and the direction finding algorithm is terminated.

[0088] (4) Calculate the direction angle of the signal. After determining the antenna group to be used, use the corresponding data to perform amplitude comparison direction finding. If the antenna group Antenna I is selected, the reference direction is NS. If the antenna group Antenna II is selected, the reference direction is NS_45. The antenna placed in the reference direction is Ant1, and the other antenna placed orthogonally is Ant2. That is: if Antenna I is selected, the antenna NS is recorded as Ant1, and the antenna EW is recorded as Ant2; if Antenna II is selected, the antenna NS_45 is recorded as Ant1, and the antenna EW_45 is recorded as Ant2. The original sampling signals of Ant1 and Ant2 are recorded as and .

[0089] IQ demodulation is performed on the two antenna signals of Ant1 and Ant2 respectively: First, the center frequency Perform mixing and obtain mixing results , , ,

[0090] (6)

[0091] Then low-pass filtering is performed, and the upper cutoff frequency of the low-pass filter LPF is Should be based on signal bandwidth Reasonable choice, generally , and get I and Q signals respectively , , ,

[0092] (7)

[0093] Then calculate the station signal amplitude observed by the two antennas based on the I / Q signal 、

[0094] (8)

[0095] Finally, the direction angle relative to the reference direction is obtained by calculating the arc tangent based on the amplitude of the two stations. ( )

[0096] (9)

[0097] (5) Determine the quadrant in which the signal is coming from. While ensuring the consistency of the antenna polarity, if Antenna I is selected, use the two antennas as coordinate axes to form a Cartesian coordinate system, with the x-axis in the EW direction, the positive direction pointing to the east, and the y-axis in the NS direction, the positive direction pointing to the north. If Antenna II is selected, use the two antennas as coordinate axes to form a Cartesian coordinate system, with the x-axis in the EW_45 direction, the positive direction pointing to the southeast, and the y-axis in the NS_45 direction, the positive direction pointing to the northeast. Rotate counterclockwise from the positive direction of the x-axis, and record the azimuth quadrants as the first, second, third, and fourth quadrants respectively.

[0098] The sampling signals of the two antennas are respectively Perform narrowband filtering to obtain very low frequency station signals 、 , and calculate the signal 、 Carrier correlation coefficient

[0099] (10)

[0100] If the correlation coefficient If the correlation coefficient is greater than 0, the VLF station signal is located in the first and third quadrants. If it is less than 0, the VLF station signal is located in the second or fourth quadrant;

[0101] If the VLF station signal is located in the first or third quadrant, the VLF station signal direction angle correction is: If the VLF station signal comes from the second or fourth quadrant, the VLF station signal direction angle is corrected to , which solves the problem of 90° direction ambiguity.

[0102] (6) Perform angle compensation. If the antenna group Antenna I is used to perform the direction finding algorithm, the true direction angle of the VLF station signal (referenced to the north direction) is If the antenna group Antenna II is used to execute the algorithm, the true direction angle of the VLF station signal needs to be compensated by 45°, which is , ;

[0103] Here That is, the direction angle of the target very low frequency signal returned by the very low frequency direction finding system relative to the true north direction.

[0104] Based on the above embodiments, this embodiment uses a specific technical implementation scheme to illustrate the technical solution of the present invention.

[0105] In this example, a digital VLF fluctuation detection system independently developed by a university was used. This system enables continuous broadband direct sampling of signals within 50 kHz at a 16-bit, 250 kHz sampling rate, effectively monitoring ELF / VLF radio electromagnetic wave signals. Based on this digital VLF fluctuation detection system, a four-channel VLF signal direction-finding system was constructed and deployed at the Suizhou Observatory (31.57°N, 113.32°E) for testing and verification. An analysis of the JJI (22.2 kHz) VLF signal transmitted from Miyazaki Prefecture, Japan, was conducted to verify the effectiveness of the VLF signal direction-finding system and method provided by this invention.

[0106] The first step is to confirm that the antenna's directionality and polarity meet the requirements, turn on the system, enter normal data acquisition mode, and obtain four-channel broadband very low frequency signal sampling data.

[0107] The second step is to process the broadband data to obtain the signal-to-noise ratio (SNR) of the JJI station signal in the two antenna groups. After comparative analysis, it was found that the JJI signal quality received by the antenna group with a 45° deflection was better. Therefore, the antenna set up with a 45° deflection was used to determine the direction of the JJI signal.

[0108] The third step is to obtain the amplitude of the JJI signal on the two orthogonal antennas through signal demodulation. AMP NS_45 and AMP EW_45 , and use the following formula to preliminarily calculate the azimuth calculate,

[0109]

[0110] The fourth step is to determine the quadrant in which the signal is coming from. The two antennas form a Cartesian coordinate system with the x-axis being EW_45, with the positive direction pointing to the southeast, and the y-axis being NS_45, with the positive direction pointing to the northeast. In a counterclockwise direction, the azimuth quadrants are recorded as the first, second, third, and fourth quadrants respectively.

[0111] The sampling signal of the two antennas = 22.2 kHz Narrowband filtering is performed to obtain the VLF station signal 、 ; Calculate signal 、 The carrier correlation coefficient corr; if the calculated correlation coefficient corr of the two-channel data of the JJI signal is greater than 0, the VLF station signal is located in the first and third quadrants; if the VLF station signal is located in the first and third quadrants, the VLF station signal direction angle is , the deflection angle of the north antenna relative to the direction of 45° is as follows Figure 3It should be noted that due to the use of a 45° deflection antenna, the true direction angle of the VLF station signal needs to be compensated by 45°, which is , .

[0112] Figure 5 The direction finding results and error distribution of the Suizhou Observatory for the 22.2kHz very low frequency signal transmitted by the Japanese JJI station within 10 seconds starting at 00:00 LT are shown in detail. Figure 5 The figure above shows the signal arrival angle (Angle of Arrival, AoA). The blue curve represents the direction finding result based on the measured data, and the green line is the theoretical reference angle of the JJI transmitter station relative to the north direction of the direction finding antenna. Figure 5 The figure below shows the error between the direction finding result and the theoretical reference value.

[0113] from Figure 5 As can be seen in the figure above, the blue curve is highly consistent with the green reference line, indicating that the direction-finding system has high direction-finding accuracy. However, there is still a certain degree of fluctuation and local peaks and valleys in the blue curve, which indicates that the actual direction-finding results are affected by the environment. Areas with large fluctuations may be related to ionospheric disturbances or changes in the geomagnetic environment, while some instantaneous deviations may be caused by very low frequency noise interference caused by strong lightning activity. In addition, because the propagation of very low frequency waves in the Earth-ionosphere waveguide is susceptible to multipath effects, phase differences in signals arriving from different paths may also cause these fluctuations. Figure 5 The figure below further illustrates the distribution of direction-finding errors. Most deviations are within ±5°, and the overall mean error is less than 5°, indicating good overall reliability of the direction-finding results. However, a small number of transient anomalies with deviations exceeding 20° can be observed in the figure. These significant deviations may be caused by short-term strong interference, such as lightning activity, electromagnetic interference, or extreme weather conditions. Furthermore, possible equipment nonlinearities or uneven directional sensitivity of the signal receiving device may also affect the direction-finding results at individual moments.

[0114] It is worth noting that the random distribution characteristics of direction finding errors ( Figure 5 The lack of significant periodicity in the fluctuations indicates that the system does not have significant systematic bias. Furthermore, the error curve shows no cumulative trend over time, indicating that the direction-finding system has good stability over a long period of time.

[0115] In summary, this direction-finding system demonstrates high accuracy and stability in monitoring the direction of very low frequency (VLF) signals, particularly with excellent error control capabilities over short timescales. Although a small number of points exhibit large instantaneous deviations exist, these issues can be further mitigated through technical optimization. In subsequent research and applications, several optimization strategies could be employed to further improve these direction-finding results. First, using deep learning algorithms to filter and suppress noise in real-time on direction-finding data can effectively reduce the impact of lightning activity or multipath propagation on direction-finding results. Second, data fusion with lightning detection data or other observational methods (such as high-precision ionospheric monitoring equipment) can further verify and correct direction-finding results with large instantaneous deviations. Furthermore, optimizing antenna design and signal reception algorithms (such as impedance matching techniques or directivity enhancement measures) can improve the device's sensitivity and direction-finding accuracy.

[0116] The ground-based multi-channel very low frequency signal direction finding system provided by the present invention is described below. The ground-based multi-channel very low frequency signal direction finding system described below and the ground-based multi-channel very low frequency signal direction finding method described above can be referred to each other.

[0117] Figure 6 FIG. 1 is a schematic structural diagram of a ground-based multi-channel very low frequency signal direction finding system provided by an embodiment of the present invention. Figure 6 As shown, it includes: a deployment module 61, a calculation module 62, a comparison module 63 and a compensation module 64, wherein:

[0118] The deployment module 61 is used to deploy a four-channel very low frequency signal direction finding system to obtain four-channel broadband very low frequency signal sampling data; the calculation module 62 is used to calculate the signal-to-noise ratio corresponding to the four-channel broadband very low frequency signal sampling data, and based on the signal-to-noise ratio, use the station direction finding algorithm to determine the effective antenna pair in the four-channel very low frequency signal direction finding system; the comparison module 63 is used to use the amplitude comparison direction finding method to calculate the signal azimuth using the effective antenna pair, determine the quadrant of the signal direction based on the signal azimuth, and output the final signal azimuth; the compensation module 64 is used to perform angle compensation on the final signal azimuth and output the actual azimuth of the measured signal.

[0119] Figure 7 An example of a physical structure diagram of an electronic device is shown below. Figure 7As shown, the electronic device may include: a processor 710, a communications interface 720, a memory 730, and a communications bus 740, wherein the processor 710, the communications interface 720, and the memory 730 communicate with each other via the communications bus 740. The processor 710 may call logic instructions in the memory 730 to execute a ground-based multi-channel very low frequency signal direction finding method, which includes: deploying a four-channel very low frequency signal direction finding system to obtain four-channel wideband very low frequency signal sampling data; calculating the signal-to-noise ratio corresponding to the four-channel wideband very low frequency signal sampling data; and determining an effective antenna pair in the four-channel very low frequency signal direction finding system using a station direction finding algorithm based on the signal-to-noise ratio; calculating a signal azimuth using the effective antenna pair using an amplitude comparison direction finding method, determining the quadrant of the signal direction based on the signal azimuth, and outputting a final signal azimuth; performing angle compensation on the final signal azimuth, and outputting the actual azimuth of the measured signal.

[0120] Furthermore, the logic instructions in the aforementioned memory 730 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 portion that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product, stored in a storage medium, includes instructions for enabling a computer device (which can be a personal computer, server, or network device, etc.) to perform all or part of the steps of the methods described in various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as a USB flash drive, a mobile hard drive, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk.

[0121] On the other hand, the present invention also provides a non-transitory computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, is implemented to execute the ground-based multi-channel very low frequency signal direction finding method provided by the above-mentioned methods, the method comprising: deploying a four-channel very low frequency signal direction finding system to obtain four-channel broadband very low frequency signal sampling data; calculating the signal-to-noise ratio corresponding to the four-channel broadband very low frequency signal sampling data, and determining the effective antenna pair in the four-channel very low frequency signal direction finding system based on the signal-to-noise ratio using a station direction finding algorithm; using the amplitude comparison direction finding method, calculating the signal azimuth using the effective antenna pair, determining the quadrant in which the signal direction is located based on the signal azimuth, and outputting the final signal azimuth; performing angle compensation on the final signal azimuth, and outputting the actual azimuth of the measured signal.

[0122] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, i.e., they may be located in one location or distributed across multiple network units. Some or all of the modules may be selected based on actual needs to achieve the objectives of the present embodiment. Persons of ordinary skill in the art will be able to understand and implement the present invention without inventive effort.

[0123] Through the above description of the embodiments, those skilled in the art will clearly understand that each embodiment can be implemented using software plus a necessary general-purpose hardware platform, or of course, hardware. Based on this understanding, the essence of the above technical solution, or the portion 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, a magnetic disk, or an optical disk, and includes a number of instructions for causing a computer device (such as a personal computer, server, or network device) to execute the methods described in each embodiment or certain portions of the embodiments.

[0124] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A ground-based multi-channel very low frequency signal direction finding method, characterized in that: include: Deploy a four-channel very low frequency (VLF) signal direction-finding system to acquire four-channel broadband VLF signal sampling data, wherein a first group of antennas in the four-channel VLF signal direction-finding system includes two orthogonal antennas in north-south and east-west directions, and a second group of antennas includes two orthogonal antennas that are tilted 45 degrees clockwise relative to the two orthogonal antennas in the first group of antennas; calculating a signal-to-noise ratio corresponding to the four-channel broadband very low frequency signal sampling data, and determining an effective antenna pair in the four-channel very low frequency signal direction finding system using a station direction finding algorithm based on the signal-to-noise ratio; Adopting the amplitude comparison direction finding method, using the effective antenna pair to calculate the signal azimuth, determining the quadrant in which the signal direction is located according to the signal azimuth, and outputting the final signal azimuth; Performing angle compensation on the final signal azimuth and outputting the actual azimuth of the measurement signal; Performing angle compensation on the final signal azimuth and outputting the actual azimuth of the measured signal includes: If the first group of antennas is used to execute the station direction finding algorithm, determining the actual azimuth of the measured signal to be the final signal azimuth; If the second group of antennas is used to execute the station direction finding algorithm, the actual azimuth of the measured signal is determined to be the final signal azimuth plus 45 degrees.

2. The ground-based multi-channel very low frequency signal direction finding method according to claim 1, characterized in that: Deployment of a four-channel VLF signal direction-finding system, including: Determine two orthogonal antennas in the first group of antennas to receive the north-south component and the east-west component of the station signal, respectively, and convert the north-south component and the east-west component of the station signal into the amplitude of the north-south magnetic field component and the amplitude of the east-west magnetic field component of the station signal; Calculating the signal northing angle based on the north-south component of the station signal and the east-west component of the station signal, or based on the amplitude of the north-south magnetic field component of the station signal and the amplitude of the east-west magnetic field component of the station signal; Determine two orthogonal antennas in the second antenna group to receive the north-south deflection component and the east-west deflection component of the station signal, respectively, and convert the north-south deflection component and the east-west deflection component of the station signal into the amplitude of the north-south deflection magnetic field component and the amplitude of the east-west deflection magnetic field component of the station signal; The north deflection angle of the signal is calculated based on the north-south deflection component of the station signal and the east-west deflection component of the station signal, or based on the amplitude of the north-south deflection magnetic field component of the station signal and the amplitude of the east-west deflection magnetic field component of the station signal.

3. The ground-based multi-channel very low frequency signal direction finding method according to claim 2, characterized in that: Calculating the signal-to-noise ratio corresponding to the four-channel broadband very low frequency signal sampling data, including: Performing fast Fourier transform on the north-south component of the station signal, the east-west component of the station signal, the north-south deflection component of the station signal, and the east-west deflection component of the station signal, and then calculating the power spectral density to obtain the power spectral density corresponding to each component; Obtaining a center frequency and a signal bandwidth of a very low frequency station signal, and determining a given noise bandwidth, wherein the noise bandwidth is greater than the signal bandwidth; A first frequency range is obtained by taking the center frequency as the midpoint and half of the signal bandwidth, and a second frequency range is obtained by taking the center frequency as the midpoint and half of the noise bandwidth; Calculating the mean of the power spectral density corresponding to each component within the first frequency range to obtain the first signal strength of each component, and calculating the mean of the power spectral density corresponding to each component within the second frequency range to obtain the second signal strength of each component; The second signal strength of each component is subtracted from the first signal strength of each component to obtain the north-south component signal-to-noise ratio, the east-west component signal-to-noise ratio, the north-south deflection component signal-to-noise ratio, and the east-west deflection component signal-to-noise ratio.

4. The ground-based multi-channel very low frequency signal direction finding method according to claim 3, characterized in that: Determining, based on the signal-to-noise ratio, an effective antenna pair in the four-channel very low frequency signal direction finding system using a station direction finding algorithm, including: Determine the minimum signal-to-noise ratio threshold; If it is determined that the north-south component signal-to-noise ratio and the east-west component signal-to-noise ratio are both greater than the minimum signal-to-noise ratio threshold, and the north-south deflection component signal-to-noise ratio and the east-west deflection component signal-to-noise ratio do not simultaneously meet the requirement of being greater than the minimum signal-to-noise ratio threshold, then using the sampled data of the first group of antennas; If it is determined that the signal-to-noise ratio of the north-south deflection component and the signal-to-noise ratio of the east-west deflection component are both greater than the minimum signal-to-noise ratio threshold, and the signal-to-noise ratio of the north-south component and the signal-to-noise ratio of the east-west component do not simultaneously meet the requirement of being greater than the minimum signal-to-noise ratio threshold, then using the sampling data of the second group of antennas; If it is determined that the north-south component signal-to-noise ratio, the east-west component signal-to-noise ratio, the north-south deflection component signal-to-noise ratio, and the east-west deflection component signal-to-noise ratio are all greater than the minimum signal-to-noise ratio threshold, then when the sum of the north-south component signal-to-noise ratio and the east-west component signal-to-noise ratio is greater than the sum of the north-south deflection component signal-to-noise ratio and the east-west deflection component signal-to-noise ratio, the sampling data of the first group of antennas is used; otherwise, the sampling data of the second group of antennas is used; If it is determined that the north-south component signal-to-noise ratio and the east-west component signal-to-noise ratio do not simultaneously satisfy the minimum signal-to-noise ratio threshold, and the north-south deflection component signal-to-noise ratio and the east-west deflection component signal-to-noise ratio do not simultaneously satisfy the minimum signal-to-noise ratio threshold, no antenna data is used and the execution of the station direction finding algorithm is terminated.

5. The ground-based multi-channel very low frequency signal direction finding method according to claim 4, characterized in that: The signal azimuth is calculated using the effective antenna pair using an amplitude comparison direction finding method, including: If the effective antenna is the first antenna group, the north-south antenna is determined to be the first antenna, and the east-west antenna is determined to be the second antenna; if the effective antenna is the second antenna group, the north-south deflection antenna is determined to be the first antenna, and the east-west deflection antenna is determined to be the second antenna; Acquire a first original sampled signal from the first antenna and a second original sampled signal from the second antenna; Performing mixing based on the center frequency, and performing IQ demodulation on the first original sampling signal and the second original sampling signal respectively to obtain a first sampled I component mixing signal, a first sampled Q component mixing signal, a second sampled I component mixing signal, and a second sampled Q component mixing signal; Determining an upper cutoff frequency of a low-pass filter according to the signal bandwidth, and performing low-pass filtering using the upper cutoff frequency to obtain a first sampled I component filtered signal, a first sampled Q component filtered signal, a second sampled I component filtered signal, and a second sampled Q component filtered signal; Calculate the first antenna station signal amplitude based on the first sampled I component filtered signal and the first sampled Q component filtered signal, and calculate the second antenna station signal amplitude based on the second sampled I component filtered signal and the second sampled Q component filtered signal; The signal azimuth is obtained according to the signal amplitude of the first antenna station and the signal amplitude of the second antenna station.

6. The ground-based multi-channel very low frequency signal direction finding method according to claim 5, characterized in that: Determining the quadrant in which the signal direction is located according to the signal azimuth, and outputting a final signal azimuth, including: A Cartesian coordinate system is constructed using the two orthogonal antenna directions of the selected antenna group as coordinate axes. If the first antenna group is selected, the x-axis is the east-west component direction, with the due east direction being the positive x-axis direction, and the y-axis is the north-south component direction, with the due north direction being the positive y-axis direction. If the second antenna group is selected, the x-axis is the east-west deflection component direction, with the southeast direction being the positive x-axis direction, and the y-axis is the north-south deflection component direction, with the northeast direction being the positive y-axis direction. The first, second, third, and fourth quadrants are determined in sequence by rotating counterclockwise from the positive x-axis of the Cartesian coordinate system. performing narrow-band filtering on the first antenna sampling signal and the second antenna sampling signal at the center frequency to obtain a first very low frequency station signal and a second very low frequency station signal, and calculating a carrier correlation coefficient between the first very low frequency station signal and the second very low frequency station signal; If it is determined that the carrier correlation coefficient is greater than 0, it is determined that the direction of the very low frequency station signal is located in the first quadrant or the third quadrant; otherwise, it is determined that the direction of the very low frequency station signal is located in the second quadrant or the fourth quadrant; If the very low frequency station signal is located in the first quadrant or the third quadrant, the final signal azimuth of the very low frequency station signal is corrected to the signal azimuth; if it is determined that the very low frequency station signal is located in the second quadrant or the fourth quadrant, the final signal azimuth of the very low frequency station signal is corrected to the negative angle corresponding to the signal azimuth.

7. A ground-based multi-channel very low frequency signal direction finding system, based on the ground-based multi-channel very low frequency signal direction finding method according to any one of claims 1 to 6, characterized in that: include: a deployment module for deploying a four-channel very low frequency (VLF) signal direction-finding system to acquire four-channel broadband VLF signal sampling data, wherein a first group of antennas in the four-channel VLF signal direction-finding system includes two orthogonal antennas in north-south and east-west directions, and a second group of antennas includes two orthogonal antennas that are tilted 45 degrees clockwise with respect to the two orthogonal antennas in the first group of antennas; a calculation module, configured to calculate a signal-to-noise ratio corresponding to the four-channel broadband very low frequency signal sampling data, and determine an effective antenna pair in the four-channel very low frequency signal direction finding system using a station direction finding algorithm based on the signal-to-noise ratio; a comparison module, configured to adopt an amplitude comparison direction finding method, use the effective antenna pair to calculate the signal azimuth, determine the quadrant in which the signal direction is located according to the signal azimuth, and output a final signal azimuth; The compensation module is used to perform angle compensation on the final signal azimuth and output the actual azimuth of the measured signal.

8. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the program, the ground-based multi-channel very low frequency signal direction finding method according to any one of claims 1 to 6 is implemented.

9. A non-transitory computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the ground-based multi-channel very low frequency signal direction finding method according to any one of claims 1 to 6 is implemented.

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