Low-frequency resonance passive identification method and device for large metal targets at sea

Abstract

The present invention relates to the technical field of positioning or existence detection using reflection or re-radiation of radio waves, and specifically to a low-frequency resonance passive identification method and device for large-scale metal targets at sea, wherein the method comprises: determining the low-frequency resonance detection frequency and channel for detecting large-scale metal targets at sea according to the scale of the large-scale targets at sea, the current ionosphere state and the electromagnetic environment, receiving the low-frequency resonance scattering signal by using a pre-constructed wide-area distributed multi-frequency cooperative receiving system, and performing resonance target identification on the large-scale targets at sea in the frequency domain and the time domain respectively by analysis, and mutually verifying the two identification results to obtain the verification result, and then obtaining the actual identification result of the large-scale metal targets at sea. The embodiment of the present invention can use medium and short wave broadcast transmission signals as metal target resonance detection signals for passive detection, and perform low-frequency resonance passive identification of large-scale metal targets at sea according to the resonance scattering mechanism and the low-frequency resonance scattering identification method.

Description

Technical Field

[0001] The invention relates to the technical field of positioning or existence detection using reflection or re-radiation of radio waves, and in particular to a low-frequency resonance passive identification method and device for large offshore metal targets. Background Art

[0002] Under ideal circumstances, high-frequency skywave over-the-horizon radar can detect, track and locate large long-range targets at sea. However, high-frequency skywave radar systems not only have high construction and operation and maintenance costs, but their receiving and transmitting signals are also greatly affected by the time-varying ionosphere and sea clutter, resulting in a high false alarm rate for target detection, a low actual detection probability, and poor positioning accuracy. They cannot classify and identify targets like high-resolution microwave radars, and need to be improved. Summary of the invention

[0003] The present invention provides a low-frequency resonance passive identification method and device for large-scale metal targets at sea, so as to solve the technical problems in the related art that the high-frequency skywave radar system has high station construction cost, low target detection probability, poor positioning accuracy and cannot classify and identify the detected targets.

[0004] The first aspect of the present invention provides a low-frequency resonance passive identification method for large offshore metal targets, comprising the following steps: determining a low-frequency resonance detection frequency and channel for detecting the large offshore target according to the scale of the large offshore target, the current ionospheric state and the electromagnetic environment, so as to use the low-frequency resonance detection frequency and channel to receive a low-frequency resonance scattering signal generated by the large offshore target, wherein the low-frequency resonance scattering signal is generated by the large offshore target according to a digital broadcast signal transmitted by a medium- and short-wave broadcast transmitter; using a pre-constructed wide-area distributed multi-frequency cooperative receiving system to receive the low-frequency resonance scattering signal, and analyzing the low-frequency resonance scattering signal to obtain an analysis result; based on the analysis result, resonant target identification is performed on the large offshore target in the frequency domain and time domain respectively to obtain corresponding frequency domain identification results and time domain identification results, and using the frequency domain identification results and the time domain identification results to mutually verify to obtain a verification result, so as to obtain an actual identification result of the large offshore metal target based on the frequency domain identification result and the time domain identification result when the verification result is a verification pass.

[0005] Optionally, in one embodiment of the present invention, the method of using a pre-built wide-area distributed multi-frequency cooperative receiving system to receive the low-frequency resonant scattered signal and analyze the low-frequency resonant scattered signal includes: within a first preset time period, using the wide-area distributed multi-frequency cooperative receiving system to receive the low-frequency resonant scattered signal at any three frequency points within a first preset frequency range, and using the echoes of the any three frequency points to determine the height of the ionospheric reflection point; within a second preset time period, based on the height, determining three clean operating frequency points within a second preset frequency range, and using the wide-area distributed multi-frequency cooperative receiving system to receive the low-frequency resonant scattered signal at the three clean operating frequency points.

[0006] Optionally, in one embodiment of the present invention, the receiving antenna of the wide-area distributed multi-frequency cooperative receiving system adopts a magneto-electrically coupled cardioid directional radiation receiving antenna with a preset receiving direction.

[0007] Optionally, in one embodiment of the present invention, the use of a pre-built wide-area distributed multi-frequency cooperative receiving system to receive the low-frequency resonant scattered signal includes: determining a target receiving channel and a target receiving station of the wide-area distributed multi-frequency cooperative receiving system based on a preset genetic algorithm and preset optimization constraints, so as to use the target receiving channel and the target receiving station to receive the low-frequency resonant scattered signal.

[0008] Optionally, in one embodiment of the present invention, based on the analysis result, resonant target identification is performed on the large offshore target in the frequency domain and time domain respectively to obtain corresponding frequency domain identification results and time domain identification results, including: using the wide-area distributed multi-frequency cooperative receiving system to collect sea surface echo signals and sea surface echo spectra; based on the sea surface echo signals and a preset spectrum peak detection method, obtaining the target echo amplitude value and the square root value of the radar scattering cross section corresponding to the first preset number of frequency points of the large offshore target at the low-frequency resonant frequency corresponding to the low-frequency resonant scattering signal; based on the sea surface echo spectrum and the preset spectrum peak detection method, obtaining the relative phase of the first target echo of the large offshore target at the first preset number of frequency points at the low-frequency resonant frequency, and the relative phase of the second target echo at the second preset number of frequency points at the low-frequency resonant frequency, wherein the difference between the first preset number of frequency points and the second preset number of frequency points is one; obtaining a set of phase characteristics based on the relative phase of the first target echo and the relative phase of the second target echo; and obtaining the frequency domain identification result according to the target echo amplitude value, phase characteristics and a preset decision plan.

[0009] Optionally, in one embodiment of the present invention, based on the analysis result, resonant target identification is performed on the large offshore target in the frequency domain and time domain respectively to obtain corresponding frequency domain identification results and time domain identification results, including: based on the sea surface echo spectrum and the preset spectrum peak detection method, obtaining the target echo amplitude and phase of the large offshore target at multiple frequency points at the low-frequency resonant frequency to obtain the complex form of the multi-frequency radar echo; performing an inverse discrete Fourier transform on the multi-frequency radar echo to obtain a time domain waveform; and obtaining the time domain identification result based on the correlation between the time domain waveform and the target time domain waveform in a preset database.

[0010] Optionally, in one embodiment of the present invention, the preset database is obtained from low-frequency resonant scattering characteristics of large offshore metal target samples at different frequencies and different incident directions.

[0011] The second aspect of the present invention provides a low-frequency resonance passive identification device for large marine metal targets, including: a determination module, which is used to determine the low-frequency resonance detection frequency and channel for detecting the large marine target according to the scale of the large marine target, the current ionosphere state and the electromagnetic environment, so as to use the low-frequency resonance detection frequency and channel to receive the low-frequency resonance scattering signal generated by the large marine target, wherein the low-frequency resonance scattering signal is generated by the large marine target according to the digital broadcast signal transmitted by the medium and short wave broadcasting transmitter; a receiving module, which is used to use a pre-built wide area distributed multi-frequency cooperative receiving system to receive the low-frequency resonance scattering signal, and analyze the low-frequency resonance scattering signal to obtain an analysis result; an identification module, which is used to perform resonance target identification on the large marine target in the frequency domain and time domain respectively based on the analysis result, so as to obtain corresponding frequency domain identification results and time domain identification results, and use the frequency domain identification results and the time domain identification results to mutually verify to obtain a verification result, so as to obtain the actual identification result of the large marine metal target based on the frequency domain identification result and the time domain identification result when the verification result is a verification pass.

[0012] Optionally, in one embodiment of the present invention, the receiving module includes: a first receiving unit, used to receive the low-frequency resonant scattered signal at any three frequency points within a first preset frequency range using the wide-area distributed multi-frequency cooperative receiving system within a first preset time period, and determine the height of the ionospheric reflection point using the echoes of the any three frequency points; a second receiving unit, used to determine three clean working frequency points within a second preset frequency range based on the height within a second preset time period, and receive the low-frequency resonant scattered signal at the three clean working frequency points using the wide-area distributed multi-frequency cooperative receiving system.

[0013] Optionally, in one embodiment of the present invention, the receiving antenna of the wide-area distributed multi-frequency cooperative receiving system adopts a magneto-electrically coupled cardioid directional radiation receiving antenna with a preset receiving direction.

[0014] Optionally, in one embodiment of the present invention, the receiving module includes: a determination unit, used to determine the target receiving channel and target receiving station of the wide-area distributed multi-frequency cooperative receiving system based on a preset genetic algorithm and preset optimization constraints, so as to utilize the target receiving channel and target receiving station to receive the low-frequency resonant scattering signal.

[0015] Optionally, in one embodiment of the present invention, the identification module includes: a collection unit, which is used to collect sea surface echo signals and sea surface echo spectra using the wide area distributed multi-frequency cooperative receiving system; a first calculation unit, which is used to obtain the target echo amplitude value and the square root value of the radar scattering cross section corresponding to the first preset number of frequency points of the large offshore target at the low-frequency resonant frequency corresponding to the low-frequency resonant scattering signal based on the sea surface echo signal and a preset spectrum peak detection method; a second calculation unit, which is used to obtain the relative phase of the first target echo of the large offshore target at the first preset number of frequency points at the low-frequency resonant frequency, and the relative phase of the second target echo at the second preset number of frequency points at the low-frequency resonant frequency based on the sea surface echo spectrum and the preset spectrum peak detection method, wherein the difference between the first preset number of frequency points and the second preset number of frequency points is one; a third calculation unit, which is used to obtain a set of phase characteristics based on the relative phase of the first target echo and the relative phase of the second target echo; a fourth calculation unit, which is used to obtain the frequency domain recognition result according to the target echo amplitude value, phase characteristics and a preset decision plan.

[0016] Optionally, in one embodiment of the present invention, the identification module includes: a fifth calculation unit, used to obtain the target echo amplitude and phase of the large offshore target at multiple frequency points at the low-frequency resonant frequency based on the sea surface echo spectrum and the preset spectrum peak detection method, so as to obtain the complex form of the multi-frequency radar echo; a sixth calculation unit, used to perform an inverse discrete Fourier transform on the multi-frequency radar echo to obtain a time domain waveform; and a seventh calculation unit, used to obtain the time domain identification result based on the correlation between the time domain waveform and the target time domain waveform in a preset database.

[0017] Optionally, in one embodiment of the present invention, the preset database is obtained from low-frequency resonant scattering characteristics of large offshore metal target samples at different frequencies and different incident directions.

[0018] A third aspect of the present invention provides an electronic device, comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the low-frequency resonance passive identification method for large offshore metal targets as described in the above embodiment.

[0019] A fourth aspect of the present invention provides a computer-readable storage medium, wherein the computer-readable storage medium stores computer instructions, and the computer instructions are used to enable the computer to execute the low-frequency resonance passive identification method for large offshore metal targets as described in the above embodiment.

[0020] A fifth aspect of the present invention provides a computer program product, including a computer program, which, when executed, is used to implement the above-mentioned low-frequency resonance passive identification method for large offshore metal targets.

[0021] The embodiment of the present invention can determine the low-frequency resonance detection frequency and channel for detecting large targets at sea based on the scale of large targets at sea, the current ionospheric state and the electromagnetic environment. On the basis of the low-frequency resonance detection frequency and channel, a pre-constructed wide-area distributed multi-frequency cooperative receiving system is used to receive the low-frequency resonance scattering signal, and the low-frequency resonance scattering signal is analyzed. Resonance target recognition is performed on large targets at sea in the frequency domain and time domain respectively, and the frequency domain recognition result and the time domain recognition result are used to verify each other to obtain the verification result. The actual recognition result of the large metal target at sea is obtained based on the frequency domain recognition result and the time domain recognition result, that is, the large metal target at sea is recognized by using the pre-constructed wide-area distributed multi-frequency cooperative receiving system. The strong resonant scattering of medium waves by the target and the reflection characteristics of medium-wave radio waves passing through the bottom of the ionosphere are used to passively detect the signals transmitted by medium and short-wave broadcasts as the resonance detection signals of metal targets, and the echo signals of the resonance scattering of the target in the low-frequency region are passively received through wide-area distributed passive reception. The target resonance scattering characteristics and geometric information carried by the target low-frequency resonance echo signal are analyzed to achieve long-range detection and identification of large metal targets on the sea surface. The target detection probability and positioning accuracy are high, and the target classification and identification can be carried out. The cost and operation and maintenance costs are low, and the anti-destruction capability is strong. In addition, the wide-area distributed collaborative reception mode is adopted, and the working frequency and detection channel can be optimized, and the detection performance of the system can be further optimized and improved. As a result, the technical problems of high station construction costs, low target detection probability, poor positioning accuracy and inability to classify and identify detected targets in the related technologies are solved.

[0022] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0024] Figure 1 A flowchart of a low-frequency resonance passive identification method for large offshore metal targets provided according to an embodiment of the present invention;

[0025] Figure 2 A schematic diagram of the electromagnetic resonance scattering principle of a large metal target at sea according to an embodiment of the present invention;

[0026] Figure 3 It is a schematic diagram of the principle of a low-frequency resonance passive identification method for large-scale metal targets at sea according to one embodiment of the present invention;

[0027] Figure 4 It is a schematic diagram of the principle of a low-frequency resonance passive identification method for large-scale metal targets at sea according to another embodiment of the present invention;

[0028] Figure 5 A schematic diagram of resonant scattering of a large target on the sea surface under irradiation of 2 MHz medium frequency electromagnetic waves according to an embodiment of the present invention;

[0029] Figure 6 A schematic diagram of resonant scattering of a large target on the sea surface under irradiation of 2 MHz medium frequency electromagnetic waves according to another embodiment of the present invention;

[0030] Figure 7 A schematic diagram of a channel optimization principle according to an embodiment of the present invention;

[0031] Figure 8 A schematic diagram of the structure of a low-frequency resonance passive identification device for large offshore metal targets provided according to an embodiment of the present invention;

[0032] Fig. 9 It is a schematic diagram of the structure of an electronic device provided according to an embodiment of the present invention. DETAILED DESCRIPTION

[0033] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0034] The following describes a low-frequency resonant passive identification method and device for large metal targets at sea according to an embodiment of the present invention with reference to the accompanying drawings. In view of the technical problems in the related technologies mentioned in the above background technology that the high-frequency skywave radar system has high station construction costs, low target detection probability, poor positioning accuracy, and cannot classify and identify the detected targets, the present invention provides a low-frequency resonant passive identification method for large metal targets at sea. In this method, the low-frequency resonant detection frequency and channel for detecting large targets at sea can be determined based on the scale of large targets at sea, the current ionospheric state, and the electromagnetic environment. On the basis of the low-frequency resonant detection frequency and channel, a pre-constructed wide-area distributed multi-frequency cooperative receiving system is used to receive low-frequency resonant scattered signals, and the low-frequency resonant scattered signals are analyzed. Resonant target identification is performed on large targets at sea in the frequency domain and time domain respectively, and the frequency domain identification results and the time domain identification results are used to verify each other to obtain The verification results show that the actual identification results of large metal targets at sea are obtained based on the frequency domain identification results and the time domain identification results. That is, the strong resonant scattering of medium waves by large metal targets at sea and the reflection characteristics of medium-wave radio waves passing through the bottom of the ionosphere are used, and the signals transmitted by medium and short wave broadcasts are used as metal target resonant detection signals for passive detection. The echo signals of the target low-frequency resonant scattering are passively received through wide-area distributed passive reception, and the target resonant scattering characteristics and geometric information carried by the target low-frequency resonant echo signals are analyzed to achieve long-range detection and identification of large metal targets on the sea surface. The target detection probability and positioning accuracy are high, and target classification and identification can be performed. The cost and operation and maintenance costs are low, and the anti-destruction capability is strong. In addition, the wide-area distributed cooperative reception mode is adopted, and the working frequency and detection channel can be optimized, and the detection performance of the system can be further optimized and improved. As a result, the technical problems of high site construction cost, low target detection probability, poor positioning accuracy and inability to classify and identify detected targets in the related technologies are solved.

[0035] Specifically, Figure 1 A schematic flow chart of a low-frequency resonance passive identification method for large offshore metal targets provided by an embodiment of the present invention.

[0036] like Figure 1 As shown, the low-frequency resonance passive identification method for large offshore metal targets includes the following steps:

[0037] In step S101, the low-frequency resonant detection frequency and channel for detecting large targets at sea are determined according to the scale of the large targets at sea, the current ionospheric state and the electromagnetic environment, so as to use the low-frequency resonant detection frequency and channel to receive the low-frequency resonant scattering signal generated by the large targets at sea, wherein the low-frequency resonant scattering signal is generated by the large targets at sea based on the digital broadcasting signal transmitted by the medium and short wave broadcasting transmitter.

[0038] In the actual implementation process, the embodiment of the present invention can select a suitable detection frequency according to the scale of the large target at sea, and make the large metal target at sea in the far field produce low-frequency resonance strong scattering, and make the sky wave propagation reflection occur at the bottom of the E layer or F layer of the ionosphere, and propagate in single mode. So that when the signal is received later, the low-frequency resonance detection frequency and channel required for reception can be determined.

[0039] In this embodiment of the present invention, the digital broadcasting signal transmitted by the medium and short wave digital broadcasting station can be used as the transmission signal for target detection.

[0040] In step S102, a pre-built wide area distributed multi-frequency cooperative receiving system is used to receive a low-frequency resonant scattered signal, and the low-frequency resonant scattered signal is analyzed to obtain an analysis result.

[0041] Among them, the receiving antenna of the wide-area distributed multi-frequency cooperative receiving system adopts a magneto-electrically coupled cardioid directional radiation receiving antenna with a preset receiving direction.

[0042] Furthermore, the embodiments of the present invention can construct a wide-area distributed multi-frequency cooperative receiving system for detection to obtain low-frequency resonant scattering signals generated by large targets at sea.

[0043] For example, the embodiment of the present invention can use the digital broadcasting signal transmitted by the medium and short wave digital broadcasting station as the transmission signal for target detection, and collect the low-frequency resonant signal scattered by the large marine target to the medium and short wave digital broadcasting signal through the pre-built wide-area distributed multi-frequency cooperative receiving system. Among them, the receiving antenna of the wide-area distributed multi-frequency cooperative receiving system adopts a magneto-electrically coupled cardioid directional radiation receiving antenna with a certain receiving direction.

[0044] After receiving the low-frequency resonant scattered signal, the embodiment of the present invention can also analyze the low-frequency resonant scattered signal to obtain an analysis result, so as to further realize the identification of large targets at sea according to the analysis result.

[0045] Optionally, in one embodiment of the present invention, a pre-built wide-area distributed multi-frequency cooperative receiving system is used to receive a low-frequency resonant scattered signal, and the low-frequency resonant scattered signal is analyzed, including: within a first preset time period, the wide-area distributed multi-frequency cooperative receiving system is used to receive the low-frequency resonant scattered signal at any three frequency points within the first preset frequency range, and the altitude of the ionospheric reflection point is determined using the echoes of any three frequency points; within a second preset time period, based on the altitude, three clean working frequency points are determined within the second preset frequency range, and the wide-area distributed multi-frequency cooperative receiving system is used to receive the low-frequency resonant scattered signal at the three clean working frequency points.

[0046] For example, an embodiment of the present invention can select three intermediate frequency points within the frequency range of 1.9±0.4 MHz to operate in a first preset time period, such as at night, so that large surface targets can undergo low-frequency strong resonant scattering, and the echoes of the three frequency points can be used to determine the height of the ionospheric reflection point.

[0047] In the second preset time period, such as daytime, under the instruction of the frequency selection system, Three clean operating frequencies are selected within the MHz frequency range to address the problem of radio wave absorption by the D layer of the ionosphere.

[0048] Optionally, in one embodiment of the present invention, a pre-built wide-area distributed multi-frequency cooperative receiving system is used to receive a low-frequency resonant scattered signal, including: determining a target receiving channel and a target receiving station of the wide-area distributed multi-frequency cooperative receiving system based on a preset genetic algorithm and preset optimization constraints, so as to receive the low-frequency resonant scattered signal using the target receiving channel and the target receiving station.

[0049] In some embodiments, the embodiments of the present invention can determine the target receiving channel and the target receiving station based on a genetic algorithm, wherein the optimization constraints are preset, that is, the optimization goal is to ensure that the receiving station is within the working frequency band, the radio wave propagation is single-mode propagation, the external electromagnetic interference is small, the signal-to-noise ratio is high, the ionosphere has little signal pollution, and the target spectrum is far away from sea clutter.

[0050] In step S103, based on the analysis results, resonant target identification is performed on large offshore targets in the frequency domain and time domain respectively to obtain corresponding frequency domain identification results and time domain identification results, and the frequency domain identification results and the time domain identification results are used to verify each other to obtain verification results. When the verification result is passed, the actual identification result of the large offshore metal target is obtained based on the frequency domain identification results and the time domain identification results.

[0051] As a possible implementation method, the embodiment of the present invention can classify and identify resonant targets in the frequency domain and the time domain, and improve the identification accuracy by mutual verification of the frequency domain identification result and the time domain identification result.

[0052] Optionally, in one embodiment of the present invention, based on the analysis results, resonant target identification is performed on large marine targets in the frequency domain and time domain respectively to obtain corresponding frequency domain identification results and time domain identification results, including: using a wide-area distributed multi-frequency cooperative receiving system to collect sea surface echo signals and sea surface echo spectra; based on the sea surface echo signals and a preset spectrum peak detection method, obtaining the target echo amplitude value and the square root value of the radar scattering cross section corresponding to the first preset number of frequency points of the large marine target at the low-frequency resonant frequency corresponding to the low-frequency resonant scattering signal; based on the sea surface echo spectrum and the preset spectrum peak detection method, obtaining the relative phase of the first target echo of the large marine target at the first preset number of frequency points at the low-frequency resonant frequency, and the relative phase of the second target echo at the second preset number of frequency points at the low-frequency resonant frequency, wherein the difference between the first preset number of frequency points and the second preset number of frequency points is one; obtaining a set of phase characteristics based on the relative phase of the first target echo and the relative phase of the second target echo; and obtaining the frequency domain identification result according to the target echo amplitude value, the phase characteristics and the preset decision plan.

[0053] The frequency domain identification method based on target low-frequency resonant scattering may include the following steps:

[0054] Step S1: Based on the sea surface echo signal collected by the wide-area distributed multi-frequency cooperative receiving system and the spectrum peak detection method, the resonance frequency of the large target is obtained. At a distance of R and direction Target echo amplitude at The square root of the radar cross section ,and .

[0055] Step S2: Based on the collected sea surface echo spectrum and the spectrum peak detection method, obtain the low-frequency resonance frequency of the large target At a distance of and direction The relative phase of the target echo at is:

[0056] (1)

[0057] in, Indicates j Resonant frequency The corresponding wavelength, is the intrinsic echo phase induced by the target, is the system phase offset.

[0058] Step S3: According to the method of step S2, calculate j +1 frequency point The relative phase of the echo on is:

[0059] (2)

[0060] Step S4: Since the system operates in the low frequency band, and and The frequency interval is small, and Electromagnetic waves have approximately the same reflection height when passing through the ionosphere, that is, , . Substituting (1)-(2) we get:

[0061] (3)

[0062] Step S5: Define a set of phase characteristics .

[0063] (4)

[0064] It can be seen that the characteristics Directly related to the inherent phase of the target, not the length of the radio wave propagation or change.

[0065] Step S6: Due to the phase is a periodic function and has multiple values, that is, ( n = integer), resulting in the characteristic is also multi-valued. To choose and , guaranteed characteristics right and uniqueness.

[0066] Step S7: Define the Euler distance between two points a and b in the feature space.

[0067] (5)

[0068] in, Reason N Amplitude characteristics and N -1 phase characteristic The feature space ( K is the normalization constant). and are the (amplitude and phase) coordinates of point a, and and are the coordinates of point b.

[0069] Step S8: Substitute the formula (5) and The relative weight between them is expressed as the ratio of their variances:

[0070] (6)

[0071] Furthermore, and is a weighting constant to make the amplitude variance equal to the phase variance, and:

[0072] (7)

[0073] in, is a weighted value, which can be calculated based on A and W The different levels of emphasis are selected.

[0074] Step 8: According to the nearest neighbor (NN) decision planning, when ( , c is the number of target types in the target feature database), indicating that it has amplitude and phase characteristics and Unknown targets can be identified as suspected targets j .

[0075] Among them, when The probability of classification error in the nearest neighbor classifier algorithm when the classification error probability of Bayesian theory is It can be expressed as:

[0076] .

[0077] Optionally, in one embodiment of the present invention, based on the analysis results, resonant target identification is performed on large offshore targets in the frequency domain and time domain respectively to obtain corresponding frequency domain identification results and time domain identification results, including: based on the sea surface echo spectrum and a preset spectrum peak detection method, obtaining the target echo amplitude and phase of the large offshore target at multiple frequency points at the low-frequency resonant frequency to obtain the complex form of the multi-frequency radar echo; performing an inverse discrete Fourier transform on the multi-frequency radar echo to obtain a time domain waveform; and obtaining a time domain identification result based on the correlation between the time domain waveform and the target time domain waveform in a preset database.

[0078] The time domain identification method based on target low-frequency resonant scattering may include the following steps:

[0079] Step S1: Based on the collected sea surface echo spectrum and the peak detection method, obtain the resonance frequency of the large target At a distance of R and direction Target echo amplitude at Value and Phase , and express the complex form of the multi-frequency radar echo as:

[0080] (9)

[0081] Step S2: Assume that the frequencies are equally spaced and are ( ). Time domain waveform Can be defined as a multi-frequency radar echo The inverse discrete Fourier transform (IDFT) is

[0082] (10)

[0083] in, , N is the number of frequency components used for measurement.

[0084] Step S3: Assume the time domain waveform is a real number, so the frequency domain waveform is f = 0 symmetric, that is ,in, for X The complex conjugate of .

[0085] If we define two time domain waveform functions and The mutual correlation coefficient is:

[0086] (11)

[0087] in, yes and The cross-correlation function is:

[0088] (12)

[0089] Step S4: Assume the time domain waveform of the unknown target is , ( ) is the database c The time domain waveform of the target, and The cross-correlation function between Obviously, for a specific waveform ,all K Value The maximum value of ,and as well as The relative time offset between them is irrelevant.

[0090] If the unknown targetj The class target has the maximum correlation, that is, ( ), then the unknown target is identified as a target j .

[0091] Optionally, in one embodiment of the present invention, the preset database is obtained from the low-frequency resonant scattering characteristics of large offshore metal target samples at different frequencies and different incident directions.

[0092] In the actual implementation process, the embodiment of the present invention can use electromagnetic field numerical methods such as the method of moments (MOM) to establish a low-frequency resonant scattering characteristic database of different frequencies and different incident directions for large metal targets at sea as a priori value for target recognition.

[0093] In summary, the embodiment of the present invention can be based on the low-frequency resonant detection frequency and channel selection, detection system composition and target recognition method based on low-frequency resonant scattering. According to the scale of large targets at sea, a suitable detection frequency is selected, and the target is caused to produce low-frequency resonant scattering; combined with the actual radio wave propagation conditions, a suitable sky wave propagation channel is selected to ensure single-mode propagation while making the sky wave reflect along the bottom of the ionosphere; by distributed reception of the signals scattered by low-frequency resonant targets at sea from medium and short wave digital radio stations, a wide-area distributed multi-frequency collaborative detection sky wave receiving system is constructed; by analyzing the signals collected by the receiving system, the resonant target classification and identification are realized in the frequency domain and time domain. The embodiment of the present invention directly uses the signals transmitted by medium and short wave broadcasting as the metal target resonant detection signal, the operating frequency is lower than that of the current sky wave radar, the radio waves are reflected by the bottom of the ionosphere, and the ionosphere has little effect on the radio waves, which is not only conducive to target detection, but also has higher positioning accuracy, and can also realize target classification and identification, good detection concealment, no need to establish a high-power transmission system, and low system construction cost. It is not only a supplement to the current large-scale target detection means at sea, but also can solve the problem that high-frequency sky wave radar cannot perform target recognition.

[0094] Combination Figures 2 to 7 As shown, the working principle of the low-frequency resonance passive identification method for large offshore metal targets according to an embodiment of the present invention is described in detail by taking an embodiment as an example.

[0095] It is understandable that electromagnetic scattering research shows that: under the irradiation of electromagnetic waves, the target will produce electromagnetic scattering into space. The scattering field depends not only on the characteristics of the target itself, but also on the frequency of the incident electromagnetic wave ( f ) is related to the target size, ranging from 1 / 2 to 10 times the target size ( L ) wavelength ( ) corresponding range, the target will produce low-frequency resonant scattering. When low-frequency resonant scattering occurs, its scattered wave is not only much stronger than the intensity of non-resonant scattering, but also carries unique information about the target's size, approximate shape, and materials used, reflecting the target's properties. In particular, Figure 2 As shown in the figure, when the macroscopic size of the metal target is at the same order of magnitude as the incident wavelength, the phase of the incident field along the length of the target changes significantly, similar to the electrostatic field. The field at each point on the scatterer is the superposition of the incident field and the scattered field caused by the remaining points on the object. The total effect of the mutual influence between the various parts of the scatterer determines the final current density distribution. The entire object participates in the scattering process. Macroscopically, the details of the target shape are not important, and its volume plays a decisive role. At this time, the target low-frequency radar cross-section value RCS is proportional to the fourth power of the incident wave frequency or wave number. Therefore, the classification and identification of the target can be achieved by measuring the radar cross section (RCS) of the low-frequency backscattering of the metal target resonance area and the intrinsic phase of the backscattering.

[0096] The technical problem to be solved by the embodiments of the present invention is mainly aimed at the common problems of existing high-frequency skywave over-the-horizon radar systems, such as complex construction, large space occupied by the transmitting and receiving antenna array, large amount of equipment, high transmission power, high site construction fee, high operation and maintenance fee, low target detection probability, poor positioning accuracy, low time utilization rate and inability to classify and identify targets. Based on the basic principles of skywave radar and the principle of low-frequency resonant scattering of metal targets, a new skywave radar technical solution is proposed.

[0097] Therefore, if Figure 3 and Figure 4 As shown, the embodiment of the present invention may be composed of three parts: low-frequency resonant detection frequency and channel selection, detection system composition, and a target recognition method based on low-frequency resonant scattering.

[0098] In the low frequency resonance detection frequency and channel selection part.

[0099] The embodiment of the present invention can select a suitable low-frequency resonance detection frequency according to the scale of large targets at sea, and cause large targets at sea in the far field to produce strong low-frequency resonance scattering, while causing sky wave propagation reflection to occur at the bottom of the E layer or F layer of the ionosphere, and to be single-mode propagation.

[0100] Furthermore, at night, three intermediate frequency points are selected within the frequency range of 1.9±0.4MHz to make large surface targets resonate and scatter, and the height of the ionospheric reflection point is determined by the echoes of the three frequency points. During the day, under the instruction of the frequency selection system, three clean working frequency points are selected within the frequency range of 7±1MHz to deal with the detection problem caused by the absorption of radio waves by the D layer of the ionosphere.

[0101] Among them, the resonant scattering of large targets on the sea surface under the irradiation of 2MHz medium-frequency electromagnetic waves can be as follows Figure 5and Figure 6 shown.

[0102] The low-frequency resonant scattering detection signal of large metal targets at sea will use the digital broadcasting signals emitted by medium and short wave digital radio stations as the transmitting signals for target detection, and by building a wide-area distributed multi-frequency collaborative receiving system, it will collect the low-frequency resonant signals scattered by large targets at sea to the medium and short wave digital broadcasting signals.

[0103] Detection system components.

[0104] The wide-area distributed multi-frequency cooperative receiving system constructed uses a magneto-electrically coupled cardioid directional radiation receiving antenna with a certain directivity.

[0105] like Figure 7 As shown, the preferred transceiver station and receiving channel will be optimized based on the genetic algorithm to optimize the receiving channel and the receiving station. Among them, the optimization goal is to ensure that the receiving station is within the working frequency band, the radio wave propagation is single-mode propagation, the external electromagnetic interference is small, the signal-to-noise ratio is high, the ionosphere has little signal pollution, and the target spectrum is far away from sea clutter.

[0106] Part of the target recognition method based on resonant scattering in the low-frequency region.

[0107] The embodiment of the present invention can analyze the low-frequency resonant scattering signal of the target collected by the receiving system, and realize the classification and identification of the resonant target in the frequency domain and the time domain.

[0108] The frequency domain identification method based on target low-frequency resonant scattering may include the following steps:

[0109] Step S1: Based on the sea surface echo signal collected by the wide-area distributed multi-frequency cooperative receiving system and the spectrum peak detection method, the resonance frequency of the large target is obtained. At a distance of R and direction Target echo amplitude at The square root of the radar cross section ,and .

[0110] Step S2: Based on the collected sea surface echo spectrum and the spectrum peak detection method, obtain the low-frequency resonance frequency of the large target At a distance of and direction The relative phase of the target echo at is:

[0111] (1)

[0112] in, Indicates j Resonant frequency The corresponding wavelength, is the intrinsic echo phase induced by the target, is the system phase offset.

[0113] Step S3: According to the method of step S2, calculate j +1 frequency point The relative phase of the echo on is:

[0114] (2)

[0115] Step S4: Since the system operates in the low frequency band, and and The frequency interval is small, and Electromagnetic waves have approximately the same reflection height when passing through the ionosphere, that is, , . Substituting (1)-(2) we get:

[0116] (3)

[0117] Step S5: Define a set of phase characteristics .

[0118] (4)

[0119] It can be seen that the characteristics Directly related to the inherent phase of the target, not the length of the radio wave propagation or change.

[0120] Step S6: Due to the phase is a periodic function and has multiple values, that is, ( n = integer), resulting in the characteristic is also multi-valued. To choose and , guaranteed characteristics right and uniqueness.

[0121] Step S7: Define the Euler distance between two points a and b in the feature space.

[0122] (5)

[0123] in, Reason N Amplitude characteristics and N -1 phase characteristic The feature space (K is the normalization constant). and are the (amplitude and phase) coordinates of point a, and and are the coordinates of point b.

[0124] Step S8: Substitute the formula (5) and The relative weight between them is expressed as the ratio of their variances:

[0125] (6)

[0126] Furthermore, and is a weighting constant to make the amplitude variance equal to the phase variance, and:

[0127] (7)

[0128] in, is a weighted value, which can be calculated based on A and W The different levels of emphasis are selected.

[0129] Step 8: According to the nearest neighbor (NN) decision planning, when ( , c is the number of target types in the target feature database), indicating that it has amplitude and phase characteristics and Unknown targets can be identified as suspected targets j .

[0130] Among them, when The probability of classification error in the nearest neighbor classifier algorithm when the classification error probability of Bayesian theory is It can be expressed as:

[0131] .

[0132] The time domain identification method based on target low-frequency resonant scattering may include the following steps:

[0133] Step S1: Based on the collected sea surface echo spectrum and the peak detection method, obtain the resonance frequency of the large target At a distance of R and direction Target echo amplitude at Value and Phase , and express the complex form of the multi-frequency radar echo as:

[0134] (9)

[0135] Step S2: Assume that the frequencies are equally spaced and are ( ). Time domain waveform Can be defined as a multi-frequency radar echo The inverse discrete Fourier transform (IDFT) is

[0136] (10)

[0137] in, , N is the number of frequency components used for measurement.

[0138] Step S3: Assume the time domain waveform is a real number, so the frequency domain waveform is f = 0 symmetric, that is ,in, for X The complex conjugate of .

[0139] If we define two time domain waveform functions and The mutual correlation coefficient is:

[0140] (11)

[0141] in, yes and The cross-correlation function is:

[0142] (12)

[0143] Step S4: Assume the time domain waveform of the unknown target is , ( ) is the database c The time domain waveform of the target, and The cross-correlation function between Obviously, for a specific waveform ,all K Value The maximum value of ,and as well as The relative time offset between them is irrelevant.

[0144] If the unknown target j The class target has the maximum correlation, that is, ( ), then the unknown target is identified as a target j .

[0145] Furthermore, the embodiment of the present invention can verify the frequency domain identification result of the target low-frequency resonant scattering and the time domain identification result of the target low-frequency resonant scattering with each other.

[0146] Furthermore, in order to illustrate the contribution of target details to the scattering field under low-frequency resonance, numerical electromagnetic field methods such as the method of moments (MOM) will be used to establish a database of low-frequency resonant scattering characteristics of large metal targets at sea with different frequencies and different incident directions, and use it as a priori value for target recognition.

[0147] In summary, the embodiments of the present invention may have the following beneficial effects:

[0148] (1) Compared with sky wave radar in related technologies, the system operates in the medium frequency band, has a low operating frequency, a narrower sea clutter spectrum, and a smaller range of clutter shielding the target, which is more conducive to target detection. At the same time, although the radio waves are reflected to the distant sea surface through the sky wave, due to the use of low frequency bands of medium frequency or short wave, the radio wave reflection occurs at the bottom of the ionosphere, the radio waves pass through the ionosphere for a short distance, and the ionosphere's temporal and spatial changes have less signal pollution on the transmitted signal and the target scattering, thereby improving the target detection probability and positioning accuracy.

[0149] (2) According to the size of the target, the system operating frequency is selected to make the target produce low-frequency resonant electromagnetic scattering, and the target echo signal is stronger. This is not only conducive to target detection, but also can utilize the low-frequency resonant scattering characteristics and geometric information carried by the target to achieve target classification and identification, which is not available in existing skywave radars.

[0150] (3) Since the detection signal uses the existing medium and short wave broadcast digital signals, only a passive receiving station needs to be established. There is no need to build a supporting high-power transmitting station like the existing high-frequency sky wave, which reduces the construction cost and operation and maintenance costs.

[0151] (4) The wide-area distributed cooperative reception mode can optimize the working frequency and detection channel, further improving the detection performance of the system.

[0152] (5) The embodiment of the present invention adopts the working principle of passive radar and uses the civilian medium wave broadcast signal as the detection signal. At the same time, based on the wide area distributed receiving mode, the receiving system has a simple structure and is easy to recover or rebuild after being destroyed, and has stronger survivability.

[0153] According to the low-frequency resonance passive identification method for large marine metal targets proposed in an embodiment of the present invention, the low-frequency resonance detection frequency and channel for detecting large marine targets can be determined based on the scale of large marine targets, the current ionospheric state and the electromagnetic environment. On the basis of the low-frequency resonance detection frequency and channel, a pre-constructed wide-area distributed multi-frequency cooperative receiving system is used to receive low-frequency resonance scattering signals, and the low-frequency resonance scattering signals are analyzed to perform resonance target identification on large marine targets in the frequency domain and time domain respectively, and the frequency domain identification results and the time domain identification results are used to verify each other to obtain the verification results, and the actual identification results of large marine metal targets are obtained based on the frequency domain identification results and the time domain identification results. The results are as follows: the strong resonant scattering of medium waves by large metal targets at sea and the reflection characteristics of medium-wave radio waves passing through the bottom of the ionosphere are utilized, and the signals transmitted by medium- and short-wave broadcasts are used as the resonant detection signals of metal targets for passive detection. The echo signals of the target low-frequency resonant scattering are passively received through wide-area distributed passive reception, and the target resonant scattering characteristics and geometric information carried by the target low-frequency resonant echo signals are analyzed to achieve long-range detection and identification of large metal targets on the sea surface. The target detection probability and positioning accuracy are high, and target classification and identification can be performed. The cost and operation and maintenance costs are low, and the anti-destruction capability is strong. In addition, the wide-area distributed collaborative reception mode is adopted, and the working frequency and detection channel can be optimized, and the detection performance of the system can be further optimized and improved. As a result, the technical problems in the related technologies that the high-frequency skywave radar system has high station construction costs, low target detection probability, poor positioning accuracy, and cannot classify and identify the detected targets are solved.

[0154] Next, the low-frequency resonance passive identification device for large offshore metal targets proposed in accordance with an embodiment of the present invention will be described with reference to the accompanying drawings.

[0155] Figure 8 It is a block diagram of a low-frequency resonance passive identification device for large offshore metal targets according to an embodiment of the present invention.

[0156] like Figure 8 As shown, the low-frequency resonance passive identification device 10 for large offshore metal targets includes: a determination module 100 , a receiving module 200 and an identification module 300 .

[0157] Specifically, the determination module 100 is used to determine the low-frequency resonant detection frequency and channel for detecting large targets at sea according to the scale of the large targets at sea, the current ionospheric state and the electromagnetic environment, so as to utilize the low-frequency resonant detection frequency and channel to receive the low-frequency resonant scattering signal generated by the large targets at sea, wherein the low-frequency resonant scattering signal is generated by the large targets at sea according to the digital broadcasting signal transmitted by the medium and short wave broadcasting transmitter.

[0158] The receiving module 200 is used to receive the low-frequency resonant scattered signal by using a pre-built wide-area distributed multi-frequency cooperative receiving system, and analyze the low-frequency resonant scattered signal to obtain an analysis result.

[0159] The identification module 300 is used to perform resonant target identification on large offshore targets in the frequency domain and time domain respectively based on the analysis results to obtain corresponding frequency domain identification results and time domain identification results, and use the frequency domain identification results and the time domain identification results to verify each other to obtain a verification result, so that when the verification result is verification passed, the actual identification result of the large offshore metal target is obtained based on the frequency domain identification results and the time domain identification results.

[0160] Optionally, in one embodiment of the present invention, the receiving module 200 includes: a first receiving unit and a second receiving unit.

[0161] Among them, the first receiving unit is used to receive low-frequency resonant scattered signals at any three frequency points within the first preset frequency range using a wide-area distributed multi-frequency cooperative receiving system within a first preset time period, and determine the height of the ionospheric reflection point using the echoes of any three frequency points.

[0162] The second receiving unit is used to determine three clean working frequency points within a second preset frequency range based on the altitude within a second preset time period, and use the wide-area distributed multi-frequency cooperative receiving system to receive low-frequency resonant scattered signals at the three clean working frequency points.

[0163] Optionally, in one embodiment of the present invention, the receiving antenna of the wide-area distributed multi-frequency cooperative receiving system adopts a magneto-electrically coupled cardioid directional radiation receiving antenna with a preset receiving direction.

[0164] Optionally, in one embodiment of the present invention, the receiving module 200 includes: a determining unit.

[0165] Among them, the determination unit is used to determine the target receiving channel and target receiving station of the wide-area distributed multi-frequency cooperative receiving system based on a preset genetic algorithm and a preset optimization constraint, so as to use the target receiving channel and the target receiving station to receive the low-frequency resonant scattered signal.

[0166] Optionally, in one embodiment of the present invention, the identification module 300 includes: a collection unit, a first calculation unit, a second calculation unit, a third calculation unit and a fourth calculation unit.

[0167] Among them, the acquisition unit is used to collect sea surface echo signals and sea surface echo spectra using a wide-area distributed multi-frequency cooperative receiving system.

[0168] The first calculation unit is used to obtain, based on the sea surface echo signal and a preset spectrum peak detection method, the target echo amplitude value and the square root value of the radar scattering cross section corresponding to the first preset number of frequency points of the large marine target at the low-frequency resonant frequency corresponding to the low-frequency resonant scattering signal.

[0169] The second calculation unit is used to obtain the relative phase of the first target echo of the large offshore target at a first preset number of frequency points at the low-frequency resonant frequency based on the sea surface echo spectrum and the preset spectrum peak detection method, and the relative phase of the second target echo at a second preset number of frequency points at the low-frequency resonant frequency, wherein the difference between the first preset number of frequency points and the second preset number of frequency points is one.

[0170] The third calculation unit is used to obtain a set of phase characteristics based on the relative phase of the first target echo and the relative phase of the second target echo.

[0171] The fourth calculation unit is used to obtain a frequency domain recognition result according to the target echo amplitude value, phase characteristics and a preset decision plan.

[0172] Optionally, in one embodiment of the present invention, the identification module 300 includes: a fifth calculation unit, a sixth calculation unit and a seventh calculation unit.

[0173] Among them, the fifth calculation unit is used to obtain the target echo amplitude and phase of a large target at sea at multiple frequency points at a low-frequency resonant frequency based on the sea surface echo spectrum and a preset spectrum peak detection method, so as to obtain the complex form of the multi-frequency radar echo.

[0174] The sixth calculation unit is used to perform inverse discrete Fourier transform on the multi-frequency radar echo to obtain a time domain waveform.

[0175] The seventh calculation unit is used to obtain a time domain recognition result based on the correlation between the time domain waveform and the target time domain waveform in a preset database.

[0176] Optionally, in one embodiment of the present invention, the preset database is obtained from the low-frequency resonant scattering characteristics of large offshore metal target samples at different frequencies and different incident directions.

[0177] It should be noted that the above explanation of the embodiment of the low-frequency resonance passive identification method for large offshore metal targets is also applicable to the low-frequency resonance passive identification device for large offshore metal targets of this embodiment, and will not be repeated here.

[0178] According to the low-frequency resonance passive identification device for large marine metal targets proposed in an embodiment of the present invention, the low-frequency resonance detection frequency and channel for detecting large marine targets can be determined based on the scale of large marine targets, the current ionospheric state and the electromagnetic environment. On the basis of the low-frequency resonance detection frequency and channel, a pre-constructed wide-area distributed multi-frequency cooperative receiving system is used to receive low-frequency resonance scattered signals, and the low-frequency resonance scattered signals are analyzed to perform resonance target identification on large marine targets in the frequency domain and time domain respectively, and the frequency domain identification results and the time domain identification results are used to verify each other to obtain the verification results, and the actual identification results of large marine metal targets are obtained based on the frequency domain identification results and the time domain identification results. The results are as follows: the strong resonant scattering of medium waves by large metal targets at sea and the reflection characteristics of medium-wave radio waves passing through the bottom of the ionosphere are utilized, and the signals transmitted by medium- and short-wave broadcasts are used as the resonant detection signals of metal targets for passive detection. The echo signals of the target low-frequency resonant scattering are passively received through wide-area distributed passive reception, and the target resonant scattering characteristics and geometric information carried by the target low-frequency resonant echo signals are analyzed to achieve long-range detection and identification of large metal targets on the sea surface. The target detection probability and positioning accuracy are high, and target classification and identification can be performed. The cost and operation and maintenance costs are low, and the anti-destruction capability is strong. In addition, the wide-area distributed collaborative reception mode is adopted, and the working frequency and detection channel can be optimized, and the detection performance of the system can be further optimized and improved. As a result, the technical problems in the related technologies that the high-frequency skywave radar system has high station construction costs, low target detection probability, poor positioning accuracy, and cannot classify and identify the detected targets are solved.

[0179] Fig. 9 A schematic diagram of the structure of an electronic device provided by an embodiment of the present invention. The electronic device may include:

[0180] A memory 901 , a processor 902 , and a computer program stored in the memory 901 and executable on the processor 902 .

[0181] When the processor 902 executes the program, the low-frequency resonance passive identification method for large offshore metal targets provided in the above-mentioned embodiment is implemented.

[0182] Furthermore, the electronic device further comprises:

[0183] The communication interface 903 is used for communication between the memory 901 and the processor 902 .

[0184] The memory 901 is used to store computer programs that can be executed on the processor 902 .

[0185] The memory 901 may include a high-speed RAM memory, and may also include a non-volatile memory (non-volatile memory), such as at least one disk memory.

[0186] If the memory 901, the processor 902 and the communication interface 903 are implemented independently, the communication interface 903, the memory 901 and the processor 902 can be connected to each other through a bus and communicate with each other. The bus can be an Industry Standard Architecture (ISA) bus, a Peripheral Component (PCI) bus or an Extended Industry Standard Architecture (EISA) bus. The bus can be divided into an address bus, a data bus, a control bus, etc. For ease of representation, Fig. 9 Only one thick line is used in the diagram, but this does not mean that there is only one bus or only one type of bus.

[0187] Optionally, in a specific implementation, if the memory 901, the processor 902 and the communication interface 903 are integrated on a chip, the memory 901, the processor 902 and the communication interface 903 can communicate with each other through an internal interface.

[0188] The processor 902 may be a central processing unit (CPU), or an application specific integrated circuit (ASIC), or one or more integrated circuits configured to implement the embodiments of the present invention.

[0189] This embodiment also provides a computer-readable storage medium on which a computer program is stored. When the program is executed by a processor, the above-mentioned low-frequency resonance passive identification method for large offshore metal targets is implemented.

[0190] An embodiment of the present invention further provides a computer program product, including a computer program, which, when executed by a processor, implements the low-frequency resonance passive identification method for large offshore metal targets provided by an embodiment of the present invention.

[0191] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or N embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0192] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "N" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0193] Any process or method description in a flowchart or otherwise described herein may be understood to represent a module, fragment or portion of code comprising one or N executable instructions for implementing the steps of a custom logical function or process, and the scope of the preferred embodiments of the present invention includes alternative implementations in which functions may not be performed in the order shown or discussed, including performing functions in a substantially simultaneous manner or in reverse order depending on the functions involved, which should be understood by technicians in the technical field to which the embodiments of the present invention belong.

[0194] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as an ordered list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by an instruction execution system, device or apparatus (such as a computer-based system, a system including a processor, or other system that can fetch instructions from an instruction execution system, device or apparatus and execute instructions), or in combination with these instruction execution systems, devices or apparatuses. For the purposes of this specification, "computer-readable medium" can be any device that can contain, store, communicate, propagate or transmit a program for use by an instruction execution system, device or apparatus, or in combination with these instruction execution systems, devices or apparatuses. More specific examples (non-exhaustive list) of computer-readable media include the following: an electrical connection with one or N wirings (electronic device), a portable computer disk box (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable and programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disk read-only memory (CDROM). In addition, the computer-readable medium may even be paper or other suitable medium on which the program is printed, since the program may be obtained electronically by optically scanning the paper or other medium and then editing, interpreting or processing in other suitable ways as necessary and then storing it in a computer memory.

[0195] It should be understood that the various parts of the present invention can be implemented by hardware, software, firmware or a combination thereof. In the above embodiment, the N steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, it can be implemented by any one of the following technologies known in the art or their combination: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0196] A person skilled in the art may understand that all or part of the steps in the method for implementing the above-mentioned embodiment may be completed by instructing related hardware through a program, and the program may be stored in a computer-readable storage medium, which, when executed, includes one or a combination of the steps of the method embodiment.

[0197] In addition, each functional unit in each embodiment of the present invention may be integrated into a processing module, or each unit may exist physically separately, or two or more units may be integrated into one module. The above-mentioned integrated module may be implemented in the form of hardware or in the form of a software functional module. If the integrated module is implemented in the form of a software functional module and sold or used as an independent product, it may also be stored in a computer-readable storage medium.

[0198] The storage medium mentioned above may be a read-only memory, a magnetic disk or an optical disk, etc. Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limiting the present invention. A person of ordinary skill in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A low-frequency resonance passive identification method for large metal targets at sea, characterized in that: The following steps are involved: Determine a low-frequency resonance detection frequency and a channel for detecting the large-scale target at sea according to the scale of the large-scale target at sea, the current ionosphere state and the electromagnetic environment, so as to receive a low-frequency resonance scattering signal generated by the large-scale target at sea by using the low-frequency resonance detection frequency and the channel, wherein the low-frequency resonance scattering signal is generated by the large-scale target at sea according to a digital broadcasting signal transmitted by a medium-wave and short-wave broadcasting transmitter; Using a pre-built wide-area distributed multi-frequency cooperative receiving system to receive the low-frequency resonant scattered signal, and analyzing the low-frequency resonant scattered signal to obtain an analysis result; Based on the analysis results, resonant target identification is performed on the large offshore target in the frequency domain and time domain respectively to obtain corresponding frequency domain identification results and time domain identification results, and the frequency domain identification results and the time domain identification results are used to verify each other to obtain verification results, so that when the verification result is verified, the actual identification result of the large offshore metal target is obtained based on the frequency domain identification results and the time domain identification results.

2. The low-frequency resonance passive identification method for large metal targets at sea according to claim 1 is characterized in that: The receiving the low-frequency resonant scattered signal by using a pre-built wide-area distributed multi-frequency cooperative receiving system and analyzing the low-frequency resonant scattered signal includes: In a first preset time period, the wide-area distributed multi-frequency cooperative receiving system is used to receive the low-frequency resonant scattered signal at any three frequency points within a first preset frequency range, and the height of the ionospheric reflection point is determined using the echoes of the any three frequency points; In a second preset time period, based on the height, three clean operating frequency points are determined within a second preset frequency range, and the wide-area distributed multi-frequency cooperative receiving system is used to receive the low-frequency resonant scattered signal at the three clean operating frequency points.

3. The low-frequency resonance passive identification method for large metal targets at sea according to claim 1 is characterized in that: The receiving antenna of the wide-area distributed multi-frequency cooperative receiving system adopts a magneto-electric coupling cardioid directional radiation receiving antenna with a preset receiving direction.

4. The low-frequency resonance passive identification method for large metal targets at sea according to claim 1 is characterized in that: The receiving of the low-frequency resonant scattered signal by using a pre-built wide-area distributed multi-frequency cooperative receiving system includes: Based on a preset genetic algorithm and preset optimization constraints, a target receiving channel and a target receiving station of the wide-area distributed multi-frequency cooperative receiving system are determined to receive the low-frequency resonant scattered signal using the target receiving channel and the target receiving station.

5. The low-frequency resonance passive identification method for large metal targets at sea according to claim 1 is characterized in that: Based on the analysis results, resonant target identification is performed on the large offshore target in the frequency domain and the time domain respectively to obtain corresponding frequency domain identification results and time domain identification results, including: The wide-area distributed multi-frequency cooperative receiving system is used to collect sea surface echo signals and sea surface echo spectra; Based on the sea surface echo signal and a preset spectrum peak detection method, obtaining the target echo amplitude value and the square root value of the radar scattering cross section corresponding to a first preset number of frequency points of the large offshore target at the low-frequency resonant frequency corresponding to the low-frequency resonant scattering signal; Based on the sea surface echo spectrum and the preset spectrum peak detection method, a relative phase of a first target echo of the large offshore target at the first preset number of frequency points at the low-frequency resonance frequency and a relative phase of a second target echo at the second preset number of frequency points at the low-frequency resonance frequency are obtained, wherein the difference between the first preset number of frequency points and the second preset number of frequency points is one; obtaining a set of phase characteristics based on the relative phase of the first target echo and the relative phase of the second target echo; The frequency domain recognition result is obtained according to the target echo amplitude value, phase characteristics and preset decision planning.

6. The low-frequency resonance passive identification method for large metal targets at sea according to claim 5 is characterized in that: Based on the analysis results, resonant target identification is performed on the large offshore target in the frequency domain and the time domain respectively to obtain corresponding frequency domain identification results and time domain identification results, including: Based on the sea surface echo spectrum and the preset spectrum peak detection method, the target echo amplitude and phase of the large offshore target at multiple frequency points at the low-frequency resonance frequency are obtained to obtain the complex form of the multi-frequency radar echo; Performing an inverse discrete Fourier transform on the multi-frequency radar echo to obtain a time domain waveform; The time domain recognition result is obtained based on the correlation between the time domain waveform and the target time domain waveform in a preset database.

7. The low-frequency resonance passive identification method for large metal targets at sea according to claim 6 is characterized in that: The preset database is obtained from the low-frequency resonant scattering characteristics of large offshore metal target samples at different frequencies and different incident directions.

8. A low-frequency resonance passive identification device for large metal targets at sea, characterized in that: include: A determination module is used to determine a low-frequency resonance detection frequency and a channel for detecting the large-scale target at sea according to the scale of the large-scale target at sea, the current ionosphere state and the electromagnetic environment, so as to use the low-frequency resonance detection frequency and the channel to receive the low-frequency resonance scattering signal generated by the large-scale target at sea, wherein the low-frequency resonance scattering signal is generated by the large-scale target at sea according to the digital broadcasting signal transmitted by the medium- and short-wave broadcasting transmitter; A receiving module, used to receive the low-frequency resonant scattered signal by using a pre-built wide-area distributed multi-frequency cooperative receiving system, and analyze the low-frequency resonant scattered signal to obtain an analysis result; An identification module is used to perform resonant target identification on the large offshore target in the frequency domain and time domain respectively based on the analysis result to obtain corresponding frequency domain identification results and time domain identification results, and use the frequency domain identification results and the time domain identification results to verify each other to obtain a verification result, so as to obtain an actual identification result of the large offshore metal target based on the frequency domain identification results and the time domain identification results when the verification result is verified.

9. An electronic device, characterized in that: include: A memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the low-frequency resonance passive identification method for large offshore metal targets as described in any one of claims 1 to 7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: The program is executed by a processor to implement the low-frequency resonance passive identification method for large offshore metal targets as described in any one of claims 1-7.

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