A method and system for underwater target detection using clutter filtering and time window power spectrum

Abstract

The present invention discloses a method and system for underwater target detection using clutter filtering and time window power spectrum. The method comprises the following steps: constructing a background field database, obtaining power frequency background field data C(t) of n areas in the sea area to be tested from the background field database. bi ; Obtain the target power frequency electromagnetic field data C(t) obtained by searching the carrier aircraft in the sea area to be tested m , according to the target power frequency electromagnetic field data C(t) m and power frequency background field data C(t) bi , calculate the power frequency electromagnetic field data C(t) of each area after clutter filtering; calculate the power frequency electromagnetic field data C(t) through the power spectrum function to obtain the time window power spectrum data of each area, and form a time window power spectrum sequence; calculate the position R of the area where the underwater ferromagnetic target is located according to the carrier search path, the carrier movement speed v and the disturbance duration T. The present invention can realize long-distance and large-scale detection of underwater ferromagnetic targets hidden under the background noise of the ocean, and meet the detection needs of vast sea areas.

Description

Technical Field

[0001] The present invention belongs to the cross field of non-acoustic underwater detection and multi-dimensional signal processing technology, and more specifically, relates to a method and system for underwater target detection using clutter filtering and time window power spectrum. Background Art

[0002] Under the new situation of economic globalization, global trade is extremely close. The total import and export volume of countries around the world, especially my country, has shown a rapid growth rate. Ship transportation is favored by global companies and merchants for its huge cargo volume and efficient cargo protection. Therefore, the number of ships built and the tonnage of ships by shipbuilding companies have increased year by year. The safety of ships during navigation has always been the focus of people's attention.

[0003] Sunken ships and ferromagnetic objects such as mines left over from wars are widely studied in marine exploration. The salvage of wrecked ships and the detection of mines require accurate positioning. At the same time, underwater shipwrecks and mines are also important factors affecting the marine navigation environment. At the same time, the increasing range of underwater submersibles and underwater robots has also become an important factor affecting marine navigation. The detection of ferromagnetic targets such as sunken ships and underwater submersibles is particularly important when ships are sailing.

[0004] Traditional underwater ferromagnetic target detection methods usually use sonar detection, which senses the target's position by receiving sonar echoes from the detected object. There are some problems with using sonar to detect underwater ferromagnetic targets such as shipwrecks. Shipwrecks are often covered by ocean mud, and sonar methods are easily interfered by the undulating terrain of the seabed, resulting in large false alarms. At the same time, acoustic detection requires the deployment of a large number of detection arrays, which is very expensive and is also easily interfered by ocean background noise. Acoustic detection methods have made it difficult to detect underwater ferromagnetic targets hidden under ocean background noise over long distances and over a large area, and cannot meet the detection needs of vast sea areas. Therefore, it is urgent to develop new non-acoustic remote sensing detection methods to detect underwater ferromagnetic targets. Summary of the invention

[0005] In view of the defects of the prior art, the purpose of the present invention is to provide a method and system for underwater target detection with clutter filtering and time window power spectrum, which can achieve long-distance and large-scale detection of underwater ferromagnetic targets hidden under the ocean background noise and meet the detection needs of vast sea areas.

[0006] To achieve the above object, in a first aspect, the present invention provides a method for underwater target detection using clutter filtering and time window power spectrum, comprising the following steps:

[0007] (1) Construct a background field database, and obtain the power frequency background field data C(t) of n areas in the sea area to be measured from the background field database bi;

[0008] (2) Obtaining the target power frequency electromagnetic field data C(t) obtained by searching the target sea area by the aircraft search path m , according to the target power frequency electromagnetic field data C(t) m and the industrial frequency background field data C(t) bi , calculate and obtain the power frequency electromagnetic field data C(t) after clutter filtering in each area;

[0009] (3) calculating the power frequency electromagnetic field data C(t) through a power spectrum function to obtain time window power spectrum data of each region to form a time window power spectrum sequence;

[0010] Among them, the power spectrum function is Where N represents the length of the power frequency electromagnetic field signal, ω represents the frequency, and t x Indicates the search time of the carrier in each area;

[0011] (4) obtaining a disturbance signal in the time window power spectrum data of each region, and determining the region where the underwater ferromagnetic target is located according to the frequency at which the disturbance signal continues to appear;

[0012] (5) Based on the aircraft search path, the aircraft movement speed v, and the disturbance duration T, the position R of the area where the underwater ferromagnetic target is located is calculated.

[0013] In one embodiment, the industrial frequency background field data C(t) bi is the power frequency simulation background field data or the power frequency measured background field data, where:

[0014] The power frequency simulation background field data is obtained by obtaining the latitude and longitude coordinates of the sea area to be measured and the dielectric layer parameters, and is calculated according to a pre-constructed power frequency power grid dipole group model;

[0015] The industrial frequency measured background field data is obtained by searching the n areas of the sea area to be measured through the carrier search path to obtain the electromagnetic field data of each frequency aliasing, and the electromagnetic field data of each frequency aliasing is extracted through short-time Fourier transform.

[0016] In one embodiment, the dielectric layer parameters include relative dielectric constant, relative magnetic permeability and relative conductivity parameters corresponding to the air layer, ocean layer, land layer, seabed layer and ionosphere.

[0017] In one embodiment, in step (2), the calculation formula of the power frequency electromagnetic field data C(t) is:

[0018] C(t)=C(t) m -kC(t) bi

[0019] In the formula, k represents the empirical coefficient, which is less than 1.

[0020] In one embodiment, in step (5), the calculation formula for the position R of the area where the underwater ferromagnetic target is located is:

[0021] R=v×T.

[0022] In one embodiment, the underwater ferromagnetic target includes an underwater shipwreck or an underwater submersible.

[0023] In a second aspect, the present invention provides an underwater target detection system with clutter filtering and time window power spectrum, comprising:

[0024] The background field data acquisition module is used to build a background field database and obtain the power frequency background field data C(t) of n areas in the sea area to be tested from the background field database. bi ;

[0025] The electromagnetic field data calculation module is used to obtain the target power frequency electromagnetic field data C(t) obtained by searching the carrier search path in the sea area to be tested. m , according to the target power frequency electromagnetic field data C(t) m and the industrial frequency background field data C(t) bi , calculate and obtain the power frequency electromagnetic field data C(t) after clutter filtering in each area;

[0026] A power spectrum sequence calculation module is used to calculate the power frequency electromagnetic field data C(t) through a power spectrum function to obtain time window power spectrum data of each region to form a time window power spectrum sequence;

[0027] Among them, the power spectrum function is Where N represents the length of the power frequency electromagnetic field signal, ω represents the frequency, and t x Indicates the search time of the carrier in each area;

[0028] The target area determination module is used to obtain the disturbance signal in the time window power spectrum data of each area, and determine the area where the underwater ferromagnetic target is located according to the frequency of continuous occurrence of the disturbance signal;

[0029] The target location calculation module is used to calculate the location R of the underwater ferromagnetic target area based on the carrier search path, the carrier movement speed v and the disturbance duration T.

[0030] The underwater target detection method and system of clutter filtering and time window power spectrum provided by the present invention utilize the disturbance generated by the industrial frequency electromagnetic field acting on the underwater ferromagnetic object, and filter out the background field data unrelated to the disturbance signal generated by the ferromagnetic object. In combination with the proposed time window power spectrum sequence analysis method, long-distance and large-scale detection of underwater ferromagnetic targets hidden in the ocean background noise can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a flow chart of a method for underwater target detection using clutter filtering and time window power spectrum provided by an embodiment of the present invention;

[0032] Figure 2 It is an architecture diagram of an underwater target detection system for clutter filtering and time window power spectrum provided by an embodiment of the present invention;

[0033] Figure 3 A simulation background image of a test site of Nantong Port provided by a specific embodiment of the present invention;

[0034] Figure 4 It is a measured background field at a test site of Nantong Port provided by a specific embodiment of the present invention;

[0035] Figure 5 It is the calculation result of the background power frequency magnetic field and submarine target disturbance provided by a specific embodiment of the present invention;

[0036] Figure 6 It is the calculation result of the background power frequency electric field and submarine target disturbance provided by a specific embodiment of the present invention;

[0037] Figure 7 It is a three-dimensional side view of the propagation of the target local abnormal power frequency magnetic field signal (after taking the logarithm) provided by a specific embodiment of the present invention;

[0038] Figure 8 It is a three-dimensional side view of the propagation of the target local abnormal power frequency electric field signal (after taking the logarithm) provided by a specific embodiment of the present invention;

[0039] Fig. 9 It is a simplified top view of a test provided by a specific embodiment of the present invention;

[0040] Fig.10 is a background field time window amplitude diagram provided by a specific embodiment of the present invention;

[0041] Fig.11 is a power spectrum diagram of a DC component magnetic field provided by a specific embodiment of the present invention;

[0042] Fig.12 It is a simplified schematic diagram of the detection radius of a carrier aircraft provided by a specific embodiment of the present invention;

[0043] Fig.13 is a magnetic field power spectrum diagram provided by a specific embodiment of the present invention;

[0044] Fig.14 is a magnetic field power spectrum diagram provided by a specific embodiment of the present invention;

[0045] Fig.15 It is a simplified schematic diagram of the sensor detection radius provided by a specific embodiment of the present invention;

[0046] Fig.16 It is an x-axis power diagram of a DC component magnetic field provided by a specific embodiment of the present invention. DETAILED DESCRIPTION

[0047] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0048] In order to solve the problem that traditional acoustic detection means are difficult to achieve long-distance and large-scale detection of underwater ferromagnetic targets hidden under the background noise of the ocean, the present invention provides an underwater target detection method using clutter filtering and time window power spectrum, which uses the industrial frequency electromagnetic field generated by power grids in various countries around the world to detect underwater ferromagnetic targets.

[0049] It should be noted that the high-voltage transmission / transformation / power consumption network throughout the world will generate power frequency electromagnetic fields. Power frequency electromagnetic fields have strong penetrability and can penetrate the ocean to act on underwater ferromagnetic targets. Under the action of the power frequency electromagnetic field (wave), the target generates a distorted signal, which can be used to detect underwater ferromagnetic targets.

[0050] Figure 1 An underwater target detection method using clutter filtering and time window power spectrum is provided in one embodiment of the present invention. Figure 1 As shown, the underwater target detection method includes steps S10 to S50, which are described in detail as follows:

[0051] S10, construct a background field database, and obtain the power frequency background field data C(t) of n areas in the sea area to be tested from the background field database bi .

[0052] In step S10, the power frequency background field data C(t) biIt can be power frequency simulation background field data or power frequency measured background field data, wherein the power frequency simulation background field data can be obtained by obtaining the latitude and longitude coordinates and dielectric layer parameters of the sea area to be measured, and calculated according to the pre-built power frequency power grid dipole group model. Specifically, different voltage level transmission networks can be selected to be simulated separately and then superimposed, three-phase simulation, to build a power frequency power grid dipole group model; set the air layer, ocean layer, land layer, seabed layer, ionosphere and several types of dielectric layers and the corresponding relative magnetic permeability mur, relative conductivity sigma and other parameters of each layer; obtain the latitude and longitude coordinates (x, y, z) of the sea area to be measured, and calculate the corresponding power frequency simulation background field data according to the power frequency power grid dipole group model.

[0053] The measured background field data of industrial frequency can be obtained by searching the electromagnetic field data of each frequency aliasing in n areas of the sea area to be measured through the carrier search path, and the electromagnetic field data of each frequency aliasing can be extracted through short-time Fourier transform.

[0054] S20, obtaining the target power frequency electromagnetic field data C(t) obtained by the carrier aircraft in turn searching in the sea area to be tested m , according to the target power frequency electromagnetic field data C(t) m and power frequency background field data C(t) bi , the power frequency electromagnetic field data C(t) after clutter filtering in each area is calculated.

[0055] Specifically, the calculation formula of the power frequency electromagnetic field data C(t) is: C(t) = C(t) m -kC(t) bi , where k represents the empirical coefficient and its value is less than 1.

[0056] S30, calculating the power frequency electromagnetic field data C(t) through a power spectrum function to obtain time window power spectrum data of each region, and forming a time window power spectrum sequence;

[0057] The power spectrum function is Where N represents the length of the power frequency electromagnetic field signal, ω represents the frequency, and t x Indicates the search time of the carrier in each area.

[0058] S40, obtaining disturbance signals in the time window power spectrum data of each region, and determining the region where the underwater ferromagnetic target is located according to the frequency at which the disturbance signals continue to appear.

[0059] In step S40, if a disturbance appears in a power spectrum of a certain time window, and the disturbance disappears in the next time window sequence, it can be considered that the disturbance is not caused by the underwater ferromagnetic target; if the disturbance signal continues to appear in the power spectrum of multiple time windows, it can be considered that the disturbance is caused by the underwater ferromagnetic target, and the area where the underwater ferromagnetic target is located can be located according to the time window power spectrum.

[0060] S50, calculating the position R of the area where the underwater ferromagnetic target is located according to the aircraft search route, the aircraft movement speed v and the disturbance duration T. Specifically, the underwater ferromagnetic target is an underwater sunken ship or an underwater submersible, etc., which is not limited in this embodiment.

[0061] Specifically, the calculation formula for the position R of the area where the underwater ferromagnetic target is located is: R=v×T.

[0062] The underwater target detection method of clutter filtering and time window power spectrum provided in this embodiment utilizes the disturbance caused by the industrial frequency electromagnetic field acting on underwater ferromagnetic objects. By filtering out background field data that is unrelated to the disturbance signal generated by the ferromagnetic objects, combined with the proposed time window power spectrum sequence analysis method, long-distance and large-scale detection of underwater ferromagnetic targets hidden in the ocean background noise can be achieved.

[0063] Figure 2 FIG. 1 is an architecture diagram of an underwater target detection system for clutter filtering and time window power spectrum provided by an embodiment of the present invention. Figure 2 As shown, the underwater target detection system includes a background field data acquisition module 100, an electromagnetic field data calculation module 200, a power spectrum sequence calculation module 300, a target area determination module 400 and a target position calculation module 500.

[0064] The background field data acquisition module 100 is used to construct a background field database and obtain the power frequency background field data C(t) of n areas in the sea area to be tested from the background field database. bi .

[0065] The electromagnetic field data calculation module 200 is used to obtain the target power frequency electromagnetic field data C(t) obtained by searching the carrier search path in the sea area to be tested. m , according to the target power frequency electromagnetic field data C(t) m and power frequency background field data C(t) bi , the power frequency electromagnetic field data C(t) after clutter filtering in each area is calculated.

[0066] The power spectrum sequence calculation module 300 is used to calculate the power frequency electromagnetic field data C(t) through the power spectrum function to obtain the time window power spectrum data of each region to form a time window power spectrum sequence;

[0067] The power spectrum function is Where N represents the length of the power frequency electromagnetic field signal, ω represents the frequency, and t x Indicates the search time of the carrier in each area.

[0068] The target area determination module 400 is used to obtain the disturbance signal in the time window power spectrum data of each area, and determine the area where the underwater ferromagnetic target is located according to the frequency of continuous occurrence of the disturbance signal.

[0069] The target location calculation module 500 is used to calculate the location R of the underwater ferromagnetic target area according to the carrier search path, the carrier movement speed v and the disturbance duration T.

[0070] Specifically, the functions of each module provided in this embodiment can be found in the detailed description of each step in the aforementioned method embodiment, and will not be described in detail in this embodiment.

[0071] The underwater target detection system with clutter filtering and time window power spectrum provided in this embodiment utilizes the disturbance caused by the industrial frequency electromagnetic field acting on underwater ferromagnetic objects, and by filtering out background field data that is unrelated to the disturbance signal generated by the ferromagnetic objects, combined with the proposed time window power spectrum sequence analysis method, it can achieve long-distance and large-scale detection of underwater ferromagnetic targets hidden in the ocean background noise.

[0072] In order to further verify the feasibility of the underwater target detection method of clutter filtering and time window power spectrum provided by the present invention, the following is a corresponding description in conjunction with specific embodiments:

[0073] 1. Establish a simulation background database

[0074] In order to construct the simulation background field database, the dipole group model of the power grid is first established. According to the current 1000kV and 500kV transmission networks of the Central China-East China-South China power grid, the 220kV transmission networks of various provinces and the 110kV transmission networks of some provinces, the power grids are simulated separately and then superimposed for three-phase simulation; the air layer, ocean layer, land layer, seabed layer, ionosphere and several types of dielectric layers and the corresponding relative magnetic permeability, conductivity and other parameters of each layer are set; the longitude and latitude coordinates of Nantong Port (32°8′6″N, 121°26′51″E) are obtained, and the altitude is 12m. The corresponding background field intensity data C(t) is obtained in the dipole group simulation model b ,like Figure 3 shown.

[0075] 2. Establish a measured background field database

[0076] When establishing the measured background field database, taking the Nantong Port test as an example, in order to analyze the power frequency magnetic field background intensity and stability of the Nantong Port test area, a variety of sensors were used to measure the power frequency magnetic field of the test dock and nearby waters in different areas. The power frequency background field data was collected at Nantong Port. The measurement method is to fix the inductive sensor and the three-axis fluxgate sensor in the measurement position for long-term continuous signal acquisition. The power frequency signal of the power frequency component is extracted by short-time Fourier transform to obtain the measured results of the power frequency background field of Nantong Port, and its average value is calculated as follows: Figure 4 shown.

[0077] The relative error can be calculated by comparing the simulated background field data with the measured data. The simulated background field intensity value at Nantong Port is 0.1nT, and the measured background field intensity average value is 0.11nT.

[0078]

[0079] Where P is the error between the measured value and the simulated value, C(t) b is the simulated background field data, C(t) f The background field data is measured, and the error is 10%.

[0080] 3. Establish a simulation target signal database

[0081] The three-phase Central China-East China-South China power grid is used as the excitation source. The underwater ferromagnetic target model is a 10,000-ton shipwreck. The target relative permeability is 500. The target is placed in the Philippine Sea with a water depth of 100m. The specific parameters of the model are shown below.

[0082] ① Grid selection: The 1000kV and 500kV grids of East China, Central China and South China and the 220kv and 110kv grids of each province are simulated separately and then superimposed, three-phase simulation;

[0083] ② Medium layer: air layer, ocean layer, land layer, seabed layer, ionosphere;

[0084] ③Target location: The target is located in the Philippine waters, at a water depth of 120m;

[0085] ④ Target parameters: radius 11m, length 170m; thickness 1.25m, magnetic permeability 500;

[0086] The specific parameter settings are as follows:

[0087] Dielectric layer Relative dielectric constant Relative magnetic permeability Conductivity (S / m) Air layer 1 1 0 Land layer 30 1 1.5 Marine layer 80 1 3 Ionosphere D 1 1 10^-8 Ionosphere 1 1 10^-4 Ionosphere F1 1 1 10^-6 Ionosphere F2 1 1 10^-8

[0088] Analysis of simulation results:

[0089] The submersible model is placed at a depth of 100m, its position coordinates are (460km, -470km), and its longitude and latitude coordinates are (132°07′12.67″E, 21°57′28.97″N). Calculate the power frequency electromagnetic field (wave) background and the magnetic disturbance calculation results of the submersible target under the combined action of the above power grid. The electromagnetic field contour map is shown in Figure 5 , Figure 6 shown.

[0090] From the results in the figure, it can be seen that the submersible interacted with the power-frequency electromagnetic field (wave) generated by the power-frequency electromagnetic radiation source, generating obvious electromagnetic anomaly signals near the target, while the background power-frequency magnetic field distribution far away from the submersible was relatively uniform. Measured at an altitude of 200m above sea level, the submersible's magnetic anomaly modulus was 1623pT, the background power-frequency magnetic field modulus was about 77pT, and the magnetic disturbance signal was about 21 times the power-frequency background magnetic field modulus.

[0091] The three-dimensional side view of the target local abnormal power frequency electric field signal (after taking the logarithm) is as follows: Figure 7 , Figure 8 As shown, in the calculation simulation of the power frequency electromagnetic field (wave) background and the magnetic disturbance of the submersible target within the range of height h above sea level, it can be seen that the target disturbance signal is significantly higher than that of the surrounding sea area.

[0092] 4. Collection of measured target database

[0093] In order to obtain target signal data and establish a measured target signal database, a special field test of a scaled model of underwater ferromagnetic targets in open sea areas was carried out. Fig. 9 The port shown is Nantong Port.

[0094] Test location: Nantong Port

[0095] Test data: fluxgate three-axis data, analyze x / y / z axis data separately;

[0096] Sampling rate: 1024Hz

[0097] AD: 24 bits; effective number 18 bits

[0098] Analysis frequency: power frequency

[0099] When measuring the passing characteristics of the target, two fluxgates were used in the test. During the test, the target was moved near the sensor, and the magnetic field signal was continuously collected and short-time Fourier analysis was performed.

[0100] 5. Time window clutter filtering and power spectrum analysis method for submersible vehicle detection

[0101] 5.1 According to the simulation of the interaction between the power frequency electromagnetic field (wave) of the dipole group and the underwater submersible, a measured background field database of the surrounding sea area is established, which is used as the background field data for the subsequent clutter filtering. Based on the background field database, the spatial background field data of the n regions of the search path are obtained, that is, C(t) i , i=1,2,3…,n

[0102] Among them, C(t) i Represents the background field data of the i-th area in the search path, and n is the number of background fields in this area.

[0103] 5.2 Based on the background field database and target signal database obtained above, the target signal is subjected to clutter filtering, namely:

[0104] C(t)=C(t) m -kC(t) i

[0105] Among them, C(t) is the signal after clutter filtering, C(t) m is the target signal without clutter filtering, C(t) i Represents the background field data of the i-th area of ​​the search path. The coefficient k is an empirical coefficient and its value is less than 1.

[0106] 5.3 Based on the analysis of the background field database and the target database, the demonstration results of the background database and the target signal database, and the corresponding sliding time window power spectrum algorithm for the industrial frequency signal C(t) filtered out by clutter.

[0107]

[0108] Among them, p(ω) is the power spectrum function, C(t) is the power frequency signal after filtering out clutter, N is the length of the power frequency signal, ω is the frequency, t x For time.

[0109] S5.4 The time power spectrum is obtained by the above algorithm. For the processed signal with a time window of ns, the same time t z , x=1…n, for {t1…t n}, forming a power spectrum sequence, namely the sliding time window power spectrum, and analyzing the obtained industrial frequency sliding time window power spectrum.

[0110] Extract the DC component from the power spectrum of the power frequency signal in the time window to form a graph of the DC component of the power spectrum of the power frequency signal over time. Use this graph to analyze the changes in the power spectrum of the target through the time window. At the same time, perform a time window power spectrum change analysis on the power spectrum of the power frequency signal with the DC component removed to observe the changes in the power spectrum of the target through the time window.

[0111] By checking the disturbance in the sliding sequence time window signal, we can see whether there is a continuous disturbance that can be judged. If there is, the disturbance is a systematic disturbance caused by the submersible or noise. Specifically, if a disturbance appears in a certain time window sequence and disappears in the next time window sequence, it can be considered that the disturbance is not caused by the target; if the disturbance signal lasts for multiple time windows, it can be considered that the disturbance is caused by the submersible and is a systematic disturbance.

[0112] S5.5 Determine the detection range of the submersible based on the DC component of the power spectrum of the power frequency signal obtained, when the power of the submersible passes through is higher than the background field threshold. When the target signal exceeds the background field threshold signal for multiple time windows, that is, C(t)>kC(t) b , where C(t) is the target signal, kC(t) b is the background field threshold signal, usually k≤1.

[0113] The detection range of the submersible can be calculated based on the submersible's movement speed, the aircraft's movement speed, and the signal duration, that is:

[0114]

[0115] Among them, R is the detection range of the submarine, is the speed of the submarine, is the airborne motion speed, and t is the signal duration.

[0116] Experiment 1

[0117] (1) The submersible can dive to a depth of 8m and is self-propelled;

[0118] (2) The aircraft scans the submersible at different altitudes above the water surface;

[0119] (3) The aircraft's flight altitude is 4.4m and 7.4m;

[0120] The aircraft's flight speed is 3.4m / s;

[0121] The submersible has a diving depth of 8m and a travel speed of 0.5m / s.

[0122] Background power frequency electromagnetic field time window acquisition Fig.10 shown.

[0123] Background field and observation point background power spectrum estimation:

[0124] First, extract the DC component as Fig.11 Shown

[0125] According to the duration of the disturbance and the speed of the carrier aircraft and the submarine, it can be calculated that when the carrier aircraft flies at a height of 5m, the sensor detection radius is about 125m.

[0126] Its simple schematic diagram is as follows Fig.12 As shown:

[0127] Power spectrum estimation after removing DC component

[0128] After obtaining the DC component in the clutter-filtered signal, the DC component is cut off to obtain a power spectrum after the DC component is removed. The power spectrum after the DC component is removed is then subjected to power spectrum analysis.

[0129] The background field power spectrum is estimated as Fig.13 Shown

[0130] Background power spectrum at observation point

[0131] Depend on Fig.14 It can be seen that when the aircraft passes by the observation point, the intensity of its power frequency electromagnetic field time window power spectrum is significantly stronger than the background field power spectrum, which can be used to determine that there is a target passing by. In other words, it can be determined whether the signal is an underwater ferromagnetic target signal.

[0132] Experiment 2

[0133] (1) The submersible dives to a depth of 19m and is stationary

[0134] (2) The aircraft sweeps back and forth at different heights above the water surface

[0135] (3) Single-carrier back-and-forth sweeping submersible

[0136] (4) The submersible sank to the bottom, with a depth of 19m

[0137] (5) Aircraft height 10m, speed 5m / s

[0138] Background field and observation point background power spectrum estimation:

[0139] According to the duration of the disturbance and the speed of the carrier aircraft and the submarine, it can be calculated that the sensor detection radius is about 112m when the carrier aircraft flies at a height of 10m.

[0140] Its simple schematic diagram is as follows Fig.15 shown.

[0141] The x-axis power spectrum is as follows Fig.16 Shown

[0142] Depend on Fig.16 It can be seen that when the carrier aircraft passes by the observation point, the intensity of its industrial frequency electromagnetic field power spectrum is obviously stronger than the background field power spectrum, which can be judged that there is a target passing by.

[0143] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for underwater target detection using clutter filtering and time window power spectrum, characterized in that: The steps include: (1) Construct a background field database, and obtain the power frequency background field data C(t) of n areas in the sea area to be measured from the background field database bi ; (2) Obtaining the target power frequency electromagnetic field data C(t) obtained by searching the target sea area by the aircraft search path m , according to the target power frequency electromagnetic field data C(t) m and the industrial frequency background field data C(t) bi , calculate and obtain the power frequency electromagnetic field data C(t) after clutter filtering in each area; (3) calculating the power frequency electromagnetic field data C(t) through a power spectrum function to obtain time window power spectrum data of each region to form a time window power spectrum sequence; Among them, the power spectrum function is Where N represents the length of the power frequency electromagnetic field signal, ω represents the frequency, and t x Indicates the search time of the carrier in each area; (4) obtaining a disturbance signal in the time window power spectrum data of each region, and determining the region where the underwater ferromagnetic target is located according to the frequency at which the disturbance signal continues to appear; (5) Based on the aircraft search path, the aircraft movement speed v, and the disturbance duration T, the position R of the area where the underwater ferromagnetic target is located is calculated.

2. The underwater target detection method of clutter filtering and time window power spectrum according to claim 1 is characterized in that: The power frequency background field data C(t) bi is the power frequency simulation background field data or the power frequency measured background field data, where: The power frequency simulation background field data is obtained by obtaining the latitude and longitude coordinates of the sea area to be measured and the dielectric layer parameters, and is calculated according to a pre-constructed power frequency power grid dipole group model; The industrial frequency measured background field data is obtained by searching the n areas of the sea area to be measured through the carrier search path to obtain the electromagnetic field data of each frequency aliasing, and the electromagnetic field data of each frequency aliasing is extracted through short-time Fourier transform.

3. The underwater target detection method of clutter filtering and time window power spectrum according to claim 2 is characterized in that: The dielectric layer parameters include relative dielectric constant, relative magnetic permeability and relative conductivity parameters corresponding to the air layer, ocean layer, land layer, seabed layer and ionosphere.

4. The underwater target detection method of clutter filtering and time window power spectrum according to claim 1 is characterized in that: In step (2), the calculation formula of the power frequency electromagnetic field data C(t) is: C(t)=C(t) m -kC(t) bi In the formula, k represents the empirical coefficient, which is less than 1.

5. The underwater target detection method of clutter filtering and time window power spectrum according to claim 1 is characterized in that: In step (5), the calculation formula for the position R of the area where the underwater ferromagnetic target is located is: R=v×T.

6. The underwater target detection method of clutter filtering and time window power spectrum according to claim 1 is characterized in that: The underwater ferromagnetic target includes an underwater shipwreck or an underwater robot.

7. An underwater target detection system with clutter filtering and time window power spectrum, characterized in that: include: The background field data acquisition module is used to build a background field database and obtain the power frequency background field data C(t) of n areas in the sea area to be tested from the background field database. bi ; The electromagnetic field data calculation module is used to obtain the target power frequency electromagnetic field data C(t) obtained by searching the carrier search path in the sea area to be tested. m , according to the target power frequency electromagnetic field data C(t) m and the industrial frequency background field data C(t) bi , calculate and obtain the power frequency electromagnetic field data C(t) after clutter filtering in each area; A power spectrum sequence calculation module is used to calculate the power frequency electromagnetic field data C(t) through a power spectrum function to obtain time window power spectrum data of each region to form a time window power spectrum sequence; Among them, the power spectrum function is Where N represents the length of the power frequency electromagnetic field signal, ω represents the frequency, and t x Indicates the search time of the carrier in each area; The target area determination module is used to obtain the disturbance signal in the time window power spectrum data of each area, and determine the area where the underwater ferromagnetic target is located according to the frequency of continuous occurrence of the disturbance signal; The target location calculation module is used to calculate the location R of the underwater ferromagnetic target area based on the carrier search path, the carrier movement speed v and the disturbance duration T.

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