A method for positioning underwater magnetic targets in marine environments

Abstract

The present invention discloses a method for locating underwater magnetic targets in a marine environment, belonging to the technical field of marine magnetic positioning. The method comprises a magnetic gradient tensor positioning system and a wave buoy. The magnetic gradient tensor positioning system comprises four three-axis fluxgate sensors, a data acquisition board and a power supply. The present invention solves the problem that direction-finding positioning only provides single angle information, suppresses noise through a specific method, further improves the positioning accuracy, makes the obtained target position information more reliable, can intuitively study the magnetic field conditions of the current sea area, and make an analysis of the positioning environment. When processing wave noise, the method is more in line with the actual situation, improves the authenticity of positioning, adopts multi-point positioning, eliminates the influence of geomagnetic tape, and does not need to perform positioning based on the geomagnetic field of the current sea area. A method for processing noise interference is adopted, and the optimal positioning relationship for selecting the measurement point position is given, thereby greatly improving the positioning accuracy.

Description

Technical Field

[0001] The present invention belongs to the technical field of marine magnetic positioning, and in particular relates to a method for positioning underwater magnetic targets in a marine environment. Background Art

[0002] Most of the large building materials of underwater weapon and equipment platforms are made of steel with ferromagnetic properties. Due to the special characteristics of the marine environment, these weapon and equipment platforms will inevitably be magnetized. The superposition and slow change of the generated magnetic field will cause magnetic field changes in the relevant area. The magnetic field changes caused by such magnetic targets are magnetic anomalies. Therefore, these objects can be identified and located by the magnetic anomaly signals detected by magnetic sensors. Underwater electromagnetic positioning technology is a passive positioning method. Compared with other technologies, it has good concealment in military operations. In addition, electromagnetic technology research has the advantages of strong penetration, short execution time, and is not easily affected by non-magnetic environments.

[0003] The existing underwater magnetic target positioning method is mainly based on the magnetic gradient tensor positioning model. In the past, domestic and foreign scholars mainly focused on the single-point magnetic gradient tensor positioning method, that is, using multiple sensors at a location point to analyze the target signal through the gradient relationship between each sensor. The single-point magnetic gradient positioning method requires the prior knowledge of the geomagnetic field value at the measurement point, so it has high requirements on the environment. In order to solve the shortcomings of this method, a two-point and multi-point magnetic gradient tensor positioning method was proposed. On the basis of the single-point positioning principle, magnetic gradient data is collected at multiple different measurement locations. The magnetic target gradient value of each measurement point and the positional relationship between the measurement points are combined to calculate the three-dimensional coordinates of the magnetic target. This method solves the influence of the geomagnetic field value of the measurement point position in single-point positioning and further improves the positioning accuracy. However, since multi-point positioning is based on the differential idea, in order to improve the positioning result, the position selection of multiple measurement points requires further analysis.

[0004] Because seawater is a conductor, due to the movement characteristics of seawater, it will cut the magnetic lines of force in the geomagnetic field and generate induced currents, which in turn generate the induced magnetic field of waves in the surrounding area. The induced magnetic field of seawater movement is the main noise source of marine electromagnetic measurement. In shallow water areas, when positioning remote targets, the induced magnetic field generated by waves will have a greater impact on the positioning process. Therefore, when performing underwater multi-point magnetic gradient tensor positioning, in addition to the selection of the measurement point position, the induced magnetic field of seawater is also an important environmental factor. Therefore, a method for underwater magnetic target positioning in a marine environment is needed to solve the above problems. Summary of the Invention

[0005] The object of the present invention is to provide a method for locating underwater magnetic targets in a marine environment to solve the problems raised in the above background technology.

[0006] To achieve the above objectives, the present invention provides the following technical solutions: a method for locating underwater magnetic targets in a marine environment, comprising a magnetic gradient tensor positioning system and a wave buoy, wherein the magnetic gradient tensor positioning system comprises four three-axis fluxgate sensors, a data acquisition board, and a power supply, and the wave buoy collects wave height and period information of seawater movement at a measurement point;

[0007] The magnetic gradient tensor positioning system also includes establishing a three-directional induced magnetic field model of ocean waves, establishing magnetic gradient positioning models of multiple positioning points, analyzing the intensity of positioning targets and ocean wave noise, and performing three-directional position inversion calculations;

[0008] The specific method of the magnetic gradient tensor positioning system is:

[0009] Step 1: When positioning is required, first obtain wave information and estimate the target position through the wave buoy, and then calculate the wave magnetic field based on the wave information;

[0010] Step 2: The signal-to-noise ratio (SNR) of the wave magnetic field calculated in step 1 and the estimated target position are judged under the position relationship. When SNR is less than 50, wave noise suppression processing, position selection between low-SNR positioning points, and high-order positioning are performed in sequence. When SNR is greater than or equal to 50, position selection between high-SNR positioning points and two-point positioning are performed in sequence. Then, high-precision multi-point positioning can be performed.

[0011] The present invention proposes a method for locating magnetic targets in a marine environment, clarifies the selection location of an underwater multi-point positioning system, the influence of the wave field, etc., and can provide a theoretical basis and technical support for the positioning method of underwater magnetic targets. In the selected positioning sea area, according to the magnetic field conditions generated by the movement of seawater at this measuring point, multiple appropriate positioning points are selected, and the position of the positioning target is inverted. In addition to eliminating the influence of geomagnetism, the influence of the induced magnetic field of seawater movement, the main magnetic interference in the marine environment, on the positioning process is reduced during positioning in shallow water areas.

[0012] As a preferred solution, the number of channels of the data acquisition board is not less than 12 channels.

[0013] As a preferred solution, the four three-axis fluxgate sensors are arranged in a cross shape to measure the magnetic gradient tensor of the target signal.

[0014] As a preferred solution, a three-directional induced magnetic field model of ocean waves is established, ocean wave information at a positioning point is obtained using a wave buoy, and the magnitude of the magnetic field in each direction of the positioning point is determined based on the ocean wave information.

[0015] As a preferred solution, a magnetic gradient positioning model of multiple positioning points is established to perform a preliminary calculation of the distance to the positioning target.

[0016] As a preferred solution, the analysis is performed on the intensity of the positioning target and the wave noise, and different multi-positioning point solutions are selected according to different positioning signal-to-noise ratios.

[0017] As a preferred solution, multiple positioning points are selected based on the analyzed ocean environment conditions, and three-directional position inversion calculations are performed on the magnetic targets in the ocean environment.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The present invention adopts a three-axis positioning method, which can directly calculate the relative coordinate position of the magnetic target in three directions in the coordinate system established by the positioning point, solving the problem that direction finding positioning only provides angle information.

[0020] The present invention considers the influence of the magnetic field generated by the movement of seawater during underwater positioning and suppresses noise through a specific method, thereby further improving the positioning accuracy and making the obtained target position information more reliable.

[0021] The present invention combines the acquired ocean wave information with the real-time situation of the current sea area, can intuitively study the magnetic field situation of the current sea area, and make an analysis of the positioning environment, which is more in line with the actual situation when processing ocean wave noise, and improves the authenticity of positioning;

[0022] The present invention adopts multi-point positioning to eliminate the influence of geomagnetic tape, and does not need to perform positioning based on the geomagnetic field of the current sea area. It also adopts a method to deal with noise interference and provides the optimal positioning relationship for selecting the measurement point position, thereby greatly improving the positioning accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a characteristic diagram of the induced magnetic field of the ocean waves of the present invention;

[0024] Figure 2 This is a model diagram of the cross-shaped structure of the magnetic gradient tensor of the present invention;

[0025] Figure 3 It is the two-point positioning coordinate diagram of the present invention;

[0026] Figure 4 This is a diagram showing the effect of the signal-to-noise ratio on the positioning system of the present invention;

[0027] Figure 5 This is a diagram showing the influence of the ocean wave magnetic field on the selection of multiple positioning positions in the present invention;

[0028] Figure 6 This is a diagram showing the effect of Kalman filtering on suppressing ocean waves.

[0029] Figure 7This is a simulation diagram of multi-point magnetic gradient positioning of the present invention;

[0030] Figure 8 This is a diagram showing the influence of the selected position on the positioning system for two-point positioning of the present invention;

[0031] Figure 9 The optimal selection path diagram for two-point magnetic gradient positioning of the present invention;

[0032] Figure 10 A relationship diagram is selected for the size of the two-point positioning interval of the present invention;

[0033] Figure 11 A regular diagram for selecting high-order positioning intervals of the present invention;

[0034] Figure 12 This is a simulation diagram of the high-order positioning measurement points of the present invention;

[0035] Figure 13 This is a flow chart of the multi-point positioning solution of the present invention;

[0036] Figure 14 This is a three-component induced magnetic field diagram generated by the ocean waves of the present invention;

[0037] Figure 15 The error map is selected for the high-order positioning position of the present invention. DETAILED DESCRIPTION

[0038] The present invention will be further described below with reference to the embodiments.

[0039] The following examples are intended to illustrate the present invention but are not intended to limit the scope of protection of the present invention. The conditions in the examples may be further adjusted according to specific conditions. Simple improvements to the method of the present invention within the scope of the present invention are also within the scope of protection claimed in the present invention.

[0040] See also Figure 1-15 The present invention provides a method for locating underwater magnetic targets in a marine environment, including a magnetic gradient tensor positioning system and a wave buoy. The magnetic gradient tensor positioning system includes four three-axis fluxgate sensors, a data acquisition board, and a power supply. The data acquisition board has no fewer than 12 channels. The four three-axis fluxgate sensors are arranged in a cross shape and are used to measure and collect the magnetic gradient tensor of the target signal. The wave buoy collects wave height and period information of the seawater movement at the measurement point.

[0041] The magnetic gradient tensor positioning system also includes establishing a three-directional induced magnetic field model of waves, establishing a magnetic gradient positioning model for multiple positioning points, analyzing the intensity of the positioning target and wave noise and three-directional position inversion calculation, establishing a three-directional induced magnetic field model of waves, using wave buoys to obtain wave information at the positioning point, determining the magnetic field size in each direction of the positioning point based on the wave information, establishing magnetic gradient positioning models for multiple positioning points, performing a preliminary calculation of the distance to the positioning target, analyzing the intensity of the positioning target and wave noise, selecting different multi-positioning point schemes based on different positioning signal-to-noise ratios, selecting multiple positioning points based on the analyzed ocean environment, and performing three-directional position inversion calculation of the magnetic target in the ocean environment;

[0042] The specific method of the magnetic gradient tensor positioning system is:

[0043] Step 1: When positioning is required, first obtain wave information and estimate the target position through the wave buoy, and then calculate the wave magnetic field based on the wave information;

[0044] Step 2: The signal-to-noise ratio (SNR) of the wave magnetic field calculated in step 1 and the estimated target position are judged under the position relationship. When SNR is less than 50, wave noise suppression processing, position selection between low-SNR positioning points, and high-order positioning are performed in sequence. When SNR is greater than or equal to 50, position selection between high-SNR positioning points and two-point positioning are performed in sequence. Then, high-precision multi-point positioning can be performed.

[0045] like Figure 2 As shown, a three-directional induced magnetic field model of ocean waves is established, and the magnitude of the ocean wave magnetic field in the current sea area is obtained based on the data collected by the wave buoy.

[0046] like Figure 2 and Figure 3 As shown, a magnetic gradient positioning model with multiple positioning points is established, two positioning points with relatively close distances are pre-selected to collect and analyze the signals of the magnetic target, and the position of the magnetic target is preliminarily calculated.

[0047] like Figure 4 、 Figure 5 and Figure 6 As shown in the figure, a magnetic gradient positioning model of multiple positioning points is established to compare and analyze the magnitude of the current target and the wave induced magnetic field. When the signal-to-noise ratio of the wave magnetic field to the target signal is SNR≥50 When the magnetic field generated by the waves has little effect on the positioning process, it is possible to directly select multiple points according to ideal conditions; when the magnetic field of the waves and the signal-to-noise ratio of the target signal are SNR＜50 When the magnetic field generated by the waves will have a greater impact on the selection of multi-point positioning positions, among which is the inclination angle from the z-axis to the xoy plane in the vertical direction; θ is the angle between the x-axis and the y-axis in the xoy horizontal plane. Therefore, when the positioning interference is strong, the wave noise needs to be suppressed first. In this invention, the optimized Kalman filter method is used to suppress the wave noise magnetic field;

[0048] like Figure 7 、 Figure 8 、 Figure 9 、 Figure 10 and Figure 12 As shown in the figure, the position inversion calculation in three directions is performed. Under the condition that the signal-to-noise ratio of the positioning environment is ideal, the positioning method based on two-point positioning is performed on the magnetic target. The influence of the selection relationship of the interval position of the two points on the positioning process is studied and analyzed. And using two-point positioning, selecting two positioning points in the vertical direction will achieve better positioning effect. In an ideal environment with less noise interference, multiple points with a vertical interval of dr = [0,0,1]m are selected for two-point real-time dynamic positioning.

[0049] Under the condition of poor signal-to-noise ratio in the positioning environment, the magnetic field noise generated by the waves is filtered, and the processed data is used for high-order three-point positioning. The selection rules of high-order positioning interval points are analyzed. Figure 11 and

[0050] Table 1, the interval positions between the measurement points meet

[0051]

[0052] in, is the vertical inclination angle between the target and the measuring point, To measure the vertical inclination between the points, select the interval position as High-order real-time dynamic positioning of multiple points of arbitrary value.

[0053] The working principle and use process of the present invention:

[0054] The principle of establishing the three-directional induced magnetic field model of ocean waves is that the movement of seawater is a random periodic motion. When the movement of seawater, a good conductor, cuts the geomagnetic field, j = σ(V × F), where V is the velocity field of the seawater and F is the total geomagnetic field of the current sea area.

[0055] In a discrete velocity field, based on the Biot-Savart law, the induced magnetic field generated by the waves is:

[0056]

[0057] Among them, the current generated by the velocity field is j=σ(-V z F y ,V z F x -Vx F z ,V x F y ), the point P(x p ,z p ) The three-directional induced magnetic field of the waves at ) is:

[0058]

[0059] The principle of establishing a magnetic gradient positioning model with multiple positioning points is as follows: four three-axis magnetic sensors are arranged in a cross-shaped array structure inside the magnetic gradient tensor system, and the magnetic gradient tensor is expressed as:

[0060]

[0061] The magnetic field strength of two points close to each other in space is: Due to the magnetic gradient tensor matrix,

[0062]

[0063] Reverse the position information of the magnetic target, that is, r = -3G -1 B;

[0064] In the single-point positioning system, the magnetic field strength of each position point of the magnetic gradient tensor system and the total magnetic field strength of the system are obtained, and r = -3G -1 B can invert the three-directional position information of the magnetic target;

[0065] The principle of establishing a magnetic gradient positioning model with multiple positioning points is as follows: the full magnetic field tensor at two points in space can be expressed as G1 and G2, where there is a magnetic gradient positioning point at a magnetic tensor system.

[0066]

[0067] in

[0068]

[0069] Then each positioning measurement point has:

[0070]

[0071] According to the relationship between the two positioning points,

[0072] r i =-(G(r i )-G(r i+1 )) -1 ·(3G(r i )+G(r i+1 ))·dl,

[0073] Where dl represents the distance between the two positioning systems;

[0074] The principle of the three-direction position inversion calculation is: based on the single-point magnetic gradient tensor positioning method, G·r=-3B, and the derivative is again obtained

[0075] Right now

[0076] Based on the differential idea and the interval relationship between the selected points, we have

[0077] r i =-4(G(r i+1 )-G(r i-1 )) -1 ·(G(r i )·(r i+1 -r i-1 )),

[0078] Among them, G(r i ) represents the magnetic gradient tensor at each measurement point;

[0079] This method needs to be verified by theoretical simulation before use. The specific simulation conditions are: the magnitude of the geomagnetic field is 47300nT, the magnetic inclination angle I = 10°, the magnetic declination angle D = 12°, and the actual information collected by the wave buoy in a certain sea area: the wave height is 2.5m, the frequency is about 0.2Hz, and the change pattern of the wave magnetic field over a period of time is as follows: Figure 14 As shown;

[0080] Assume that the positioning distance is [100, 120, 10] m and the magnetic moment of the magnetic target is In the magnetic field environment generated by the current wave motion, the signal-to-noise ratio between the magnetic target and the wave magnetic field noise is 38dB, so the wave noise needs to be suppressed.

[0081] Initial position According to the given technical solution, the spacing is selected as More points, by Figure 15 The optimal positioning point interval is verified to be dr = [sin(35°)cos(θ r ),sin(35°)sin(θ r ),cos(35°)]m; when this positioning point interval is selected, high-order positioning of the sampling points is performed.

[0082] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for locating underwater magnetic targets in a marine environment, comprising a magnetic gradient tensor positioning system and a wave buoy, characterized in that: The magnetic gradient tensor positioning system includes four three-axis fluxgate sensors, a data acquisition board and a power supply. The wave buoy collects wave height and period information of the seawater movement at the measurement point; The magnetic gradient tensor positioning system also includes establishing a three-directional induced magnetic field model of ocean waves, establishing magnetic gradient positioning models of multiple positioning points, analyzing the intensity of positioning targets and ocean wave noise, and performing three-directional position inversion calculations; The specific method of the magnetic gradient tensor positioning system is: Step 1: When positioning is required, first obtain wave information and estimate the target position through the wave buoy, and then calculate the wave magnetic field based on the wave information; Step 2: The signal-to-noise ratio (SNR) of the wave magnetic field calculated in step 1 and the estimated target position are judged under the position relationship. When SNR is less than 50, wave noise suppression processing, position selection between low-SNR positioning points, and high-order positioning are performed in sequence. When SNR is greater than or equal to 50, position selection between high-SNR positioning points and two-point positioning are performed in sequence. Then, high-precision multi-point positioning can be performed.

2. The method for locating underwater magnetic targets in a marine environment according to claim 1, wherein: The number of channels of the data acquisition board is not less than 12 channels.

3. The method for locating underwater magnetic targets in a marine environment according to claim 1, wherein: The four three-axis fluxgate sensors are arranged in a cross shape and are used to measure the magnetic gradient tensor of the target signal.

4. The method for locating underwater magnetic targets in a marine environment according to claim 1, wherein: The three-directional induced magnetic field model of the ocean waves is established, the ocean wave information at the positioning point is obtained by using the wave buoy, and the magnitude of the magnetic field in each direction of the positioning point is determined based on the ocean wave information.

5. The method for locating underwater magnetic targets in a marine environment according to claim 1, wherein: The magnetic gradient positioning model of multiple positioning points is established to perform a preliminary calculation of the distance to the positioning target.

6. The method for locating underwater magnetic targets in a marine environment according to claim 1, wherein: The analysis is based on the intensity of the positioning target and the wave noise, and different multi-positioning point solutions are selected according to different positioning signal-to-noise ratios.

7. The method for locating underwater magnetic targets in a marine environment according to claim 1, characterized in that: According to the analyzed ocean environment, multiple positioning points are selected and the three-directional position inversion calculation of the magnetic targets in the ocean environment is performed.

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