Cooperative laser direction finding device

Abstract

The invention provides a cooperative laser direction finding device. The device comprises a hardware part and an algorithm part with a laser spot center extraction function, wherein the hardware part consists of a laser transmitting module, a direction-finding receiving module, a signal processing module and a searching, capturing and tracking module. When the two cooperative laser direction finding devices work, the two cooperative laser direction finding devices oppositely emit laser to transmit laser signals. When a direction-finding receiving module in the laser direction-finding device does not receive the laser spot, the laser direction-finding device searches and captures the laser signal firstly until the area array sensor receives the laser signal, and an image with the laser spot is generated. And based on the obtained laser spot image, the laser direction-finding device uses a center extraction algorithm based on Gaussian fitting to solve the spot coordinate of the laser of the opposite side on the own direction-finding sensor, and the direction information of the laser transmitting side relative to the receiving side is obtained according to the spot coordinate position information.

Description

Technical Field

[0001] The present invention discloses a cooperative laser direction finding device, which involves using a cooperative measurement method to realize direction measurement between cooperative aircrafts through the interactive cooperation of a laser emission module, a direction finding receiving module, a signal processing module, and a search, capture, and tracking module, etc., belonging to the field of navigation technology. Background Art

[0002] In recent years, aircraft swarm flight has received increasing attention. Formation flight can greatly improve mission efficiency due to its advantages such as rapid operation, wide coverage, and ability to perform multiple tasks. In multi-aircraft swarm flight, the premise of tasks such as task allocation, trajectory planning, and formation control is the perception of the position information of formation members. For example, tasks such as target navigation information transmission and terrain stereo imaging require that formation members can share accurate relative position, attitude, speed and other information. Therefore, collaborative navigation technology is crucial to formation flight missions and is a key factor that directly affects the realization of aircraft formation missions.

[0003] At present, the main navigation methods for formation flight collaborative navigation include inertial navigation, satellite navigation, radio navigation, etc. After the initial alignment of inertial navigation, the navigation accuracy will decrease with time. Satellite navigation requires the support of ground station equipment and is easily interfered with. Radio navigation has weak anti-interference ability and cannot function in a radio denial environment. For the complex, changeable and harsh aircraft formation flight environment in the future, the currently commonly used navigation methods are difficult to meet the requirements. A navigation method that can achieve high precision, high reliability and high autonomy in a long-distance and poor lighting environment is needed. Laser navigation technology provides a feasible technical approach to deal with such conditions.

[0004] Laser navigation technology measures the distance and direction by emitting lasers and capturing the reflected light beams by sensors to determine the relative position of target objects, thereby achieving high-precision relative positioning and navigation. In recent years, laser technology has continued to develop. On the one hand, the frequency width of laser light sources has become narrower, and the monochromaticity has been greatly improved, which strongly supports precision laser measurement; on the other hand, the divergence angle of laser beams has become smaller, and the directionality has been further enhanced, allowing laser measurements to maintain high accuracy over long distances. The above advantages of laser navigation have led to its application in aerospace fields such as spacecraft rendezvous and docking, and space communications.

[0005] One of the important technical foundations of laser navigation is laser direction finding technology. Laser direction finding technology mainly refers to the technology of controlling the laser emission system to emit laser pulse signals with specific properties, and then using the detector to collect the signal and use the relative energy information of the light spot on the surface to solve the target's azimuth information. It is currently used in laser early warning and laser guidance. The first application of laser direction finding technology was the American "Paveway I" precision laser weapon system in the 1970s. The system used a laser semi-active positioning system that could accurately locate and track stationary targets. Experimental results show that the system significantly improves the weapon's hit rate, and the landing point can be guaranteed to be within 1.5m of the target. Since laser direction finding systems are usually used in precision weapon systems, there is very little research information open to related fields abroad.

[0006] Domestic research on laser direction finding technology mainly focuses on improving accuracy. In 2017, Li Hui and others from the Luoyang Electronic Equipment Test Center of China analyzed the influence of external interference torques such as detector noise, projectile disturbance, and projectile friction on the accuracy of laser direction finding. According to the control principle of the laser direction finding system, a stable tracking loop model was established, and the influence of these external error factors on the stable tracking performance of the direction finding system and the output of the projectile-eye line of sight angular velocity was quantitatively analyzed. The noise characteristics of the output of the projectile-eye line of sight angular velocity of the direction finding system were analyzed through actual measurement, and the mathematical relationship between noise and measurement distance was established, and simulation calculations were performed. In 2017, Ning Min from Harbin Institute of Technology analyzed and proposed a laser direction finding system based on polarization detection, and gave a direction finding information solution algorithm under polarization detection mode. A verification system was built for signal-to-noise ratio experiments and direction finding information solution verification experiments, and the system's angular measurement accuracy was improved with the help of the Kalman filter algorithm. In 2019, Chen Hongda from Changchun University of Science and Technology designed a laser direction finding system based on a four-quadrant detector with laser guidance as the application background. He used FPGA and high-speed analog-to-digital conversion chip AD9226 to collect direction finding information, and improved the measurement accuracy by adding pseudo-random codes and gate locking. He proposed an improved laser spot positioning fitting algorithm by integrating geometric approximation method and polynomial fitting method, and proved the superiority of the improved algorithm through experiments.

[0007] In summary, the navigation methods commonly used in formation flying cannot meet the long-term, high-precision, anti-interference, and high-timeliness navigation requirements of the collaborative navigation system in formation flying. Laser direction finding technology has many advantages such as high precision, high timeliness, and anti-interference, and has great advantages in the application of collaborative navigation in multi-aircraft formation flying. However, due to the problem of energy intensity attenuation, current laser direction finding is mostly used in close-range environments. Therefore, increasing signal strength by reducing the transmission path and other means has great engineering significance for the application in collaborative navigation. In response to this problem, the present invention proposes a cooperative laser direction finding device, which uses a laser-sensitive array sensor to receive laser signals, generates an image with a laser spot, and obtains high-precision target relative position information based on the image. Summary of the invention

[0008] Aiming at the demand for high-precision laser direction finding in cooperative navigation of multi-aircraft formation flight, the present invention provides a cooperative laser direction finding device. The advantages of the present invention are: on the one hand, by adopting a cooperative direction finding method, the propagation distance of the laser in the atmosphere is reduced and the diffuse reflection process is avoided, which can significantly improve the energy intensity of the received laser signal and significantly increase the allowable measurement distance of the laser in the atmosphere; on the other hand, a high-resolution area array sensor and a center extraction algorithm based on Gaussian fitting are used to realize laser direction finding, and support is provided for the realization of laser alignment.

[0009] The main technical solution of the present invention is: two cooperative laser direction finding devices emit lasers in opposite directions to transmit laser signals. When the direction finding receiving module in the laser direction finding device does not receive the laser spot, the laser direction finding device first searches and captures the laser signal until the laser signal is received using the area array sensor to generate an image with the laser spot. Based on the obtained laser spot image, the laser direction finding device uses a center extraction algorithm based on Gaussian fitting to solve the spot coordinates of the other party's laser on its own direction finding sensor, and the direction information of the laser emitter relative to the receiver can be obtained based on the spot coordinate position information.

[0010] The laser direction finding device of the present invention comprises a hardware part and an algorithm part with a laser spot center extraction function. Here, the hardware composition of the laser direction finding device consisting of a laser transmitting module, a direction finding receiving module, a signal processing module and a search, capture and tracking module is used as an example to explain the composition and principle of the device in detail.

[0011] (I) Hardware composition of module-based laser direction finding device

[0012] The laser direction finding device can be composed of four modules: laser emission module, direction finding receiving module, signal processing module and search capture tracking module. The content and function of each module are as follows:

[0013] 1. Module S1, laser emission module. This module has the function of emitting laser pulses, with a peak power of up to 5kW and a beam divergence angle of less than 10mrad. It can use passive Q-switched laser technology to compress the continuous laser energy output into extremely narrow pulses for emission, thereby increasing the peak power of the light source by several orders of magnitude, and achieving higher accuracy and reliability for long-distance measurement;

[0014] 2. Module S2, direction finding receiving module. This module includes an InGaAs array sensor for laser imaging, an optical system with a filtering function to reduce the sensor imaging background noise, and an ISP signal processing circuit. It has the function of receiving laser spots and imaging, and can receive and image the laser emitted by cooperative targets;

[0015] 3. Module S3, signal processing module. This module includes FPGA chip, serial communication chip and supporting circuits, etc. It can realize laser trigger program, direction finding receiving program and direction finding image processing program, and has the functions of signal processing, communication control and algorithm implementation for each submodule. Among them, the laser trigger program uses the global clock input by FPGA to define a suitable frequency division counter to obtain the TTL signal required for the laser to emit laser; the direction finding receiving program uses the data interaction between the FPGA chip and the camera based on the network port to initialize the camera first, control the camera to take pictures and store images, and send the grayscale data obtained by the camera through the serial communication protocol and save it to the ARM core in the FPGA chip; the direction finding image processing program will receive the grayscale image data containing the laser, and solve the center coordinates of the light spot in the ARM core through the center extraction algorithm based on Gaussian fitting; the supporting circuits include laser circuits and power supply circuits, which need to meet the electrical requirements of each device so that the equipment can work normally, while also taking into account the equipment performance and appearance volume requirements.

[0016] 4. Module S4, search, capture and tracking module. This module has a two-dimensional posture rotation function and can adjust the posture according to the spot position information given by the signal processing module to achieve the alignment of the transmitting and receiving optical paths.

[0017] The above modules work together to realize the cooperative laser direction finding function. First, the cooperative aircraft transmits laser signals to the cooperative target through the laser emission module; second, before the direction finding receiving module receives the laser spot, the signal processing module drives the search capture tracking module to search; then, after the direction finding receiving module receives the laser spot, the signal processing module uses the center extraction algorithm based on Gaussian fitting to solve the spot coordinates of the opponent's laser on the own direction finding sensor, thereby determining the opponent's direction information.

[0018] (II) Center extraction algorithm based on Gaussian fitting

[0019] In the laser direction finding device of the direction finding receiver, the signal processing module first performs threshold segmentation on the received grayscale image data containing the laser spot, and then calculates the coordinates of the spot through a center extraction algorithm based on Gaussian fitting.

[0020] The laser spot image can be divided into three parts according to the threshold value: the background of the image (area A), that is, the area outside the laser beam; the part with Gaussian light intensity distribution but noise (area B); and the part with saturated gray value in the center of the laser spot (area C). Therefore, it is necessary to extract area B as the sampling point first.

[0021] After obtaining the sampling points, the spot coordinates can be solved by the center extraction algorithm based on Gaussian fitting. Ideally, on the cross section (x, y) perpendicular to the emission direction of the laser beam, the light intensity should satisfy the Gaussian distribution described by the following formula:

[0022]

[0023] Where: I(x,y) is the light intensity at the cross section (x,y); H is the light intensity amplitude of the cross section; are the variances of the light intensity distribution in the x and y directions respectively. (x0, y0) are the coordinates of the center of the light spot; from the above formula, it can be seen that the position where the light intensity is equal to the amplitude is the center of the light spot. Take the logarithm of both sides of the above formula and arrange it into a quadratic polynomial as shown below:

[0024] z=ax 2 +by 2 +cx+dy+e (2)

[0025] The corresponding relationship of its parameters is:

[0026]

[0027] Take the residual as:

[0028]

[0029] Where: (x i ',y i ')∈E represents the set of sampling points in the image that satisfy the two-dimensional Gaussian distribution, (x i ',y i ') is the coordinate of the image point, z i ' is the natural logarithm of the light intensity at that point. According to the least squares principle (minimum residual sum of squares), a, b, c, d, e, and f can be determined by formula (3):

[0030]

[0031] In this problem, the number of unknowns is 5 and the number of independent equations is n. Matrix theory gives the best square solution of the equation system of the form AX=b when the number of independent equations is greater than the number of unknowns: X=A + b, where A + represents the MP generalized inverse of the matrix A. In this problem, we need to find the generalized inverse of the matrix A in the following formula:

[0032]

[0033] The matrix is ​​a column-full rank matrix, and its generalized inverse matrix can be solved using the following formula:

[0034] A + =(A H A) - A H (7)

[0035] For a real matrix, A H Represents its symmetric matrix, then the solution of the vector composed of unknown numbers is:

[0036]

[0037] make

[0038]

[0039]

[0040] Then there is

[0041]

[0042]

[0043] BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a schematic diagram of the principle of a cooperative laser direction-finding device.

[0045] Figure 2 It is a schematic diagram of the modular scheme of the cooperative laser direction-finding device.

[0046] Figure 3 It is a flowchart of cooperative laser direction finding. DETAILED DESCRIPTION

[0047] The following will be combined with the accompanying drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. The described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. The composition and working principle of the cooperative laser direction finding device are shown in the attached figure. Figure 1 With attached Figure 2 As shown, Figure 1 The spatial coordination relationship between the laser transmitting module, direction finding receiving module and search and capture module in the cooperative laser direction finding device is intuitively demonstrated. Figure 2 The logical relationship between the modules in the cooperative laser direction finding device during operation is explained. Figure 1 With attached Figure 2 The working principle of the cooperative laser direction finding device is shown below. Figure 3 The present invention is further described in detail through the following four steps from the perspective of specific implementation:

[0048] Step 1: The cooperative laser direction finding device transmits a laser signal to the cooperative target through the laser emission module, and searches for the laser signal through the search, capture and tracking module. If either party searches for the laser signal, continue to step 1; otherwise, proceed to step 2;

[0049] Step 2: The party that has searched for the laser signal obtains the grayscale image data containing the laser spot received by the area array sensor, stores it and executes step 3;

[0050] Step 3: The signal processing module processes the grayscale image data containing the laser spot using a center extraction algorithm based on Gaussian fitting to obtain the center coordinates of the laser spot, thereby obtaining the laser direction finding result, and then executes step 4;

[0051] Step 4: Determine whether the laser direction finding task is completed. If it is completed, the laser direction finding device stops working; otherwise, return to step 1.

Claims

1. A cooperative laser direction finding device, characterized in that: The hardware part includes the following modules:

1. Module S1, laser emission module. This module has the function of emitting laser pulses and can use passive Q-switched laser technology; 2. Module S2, direction finding receiving module. This module includes an InGaAs array sensor, an optical system, and an ISP signal processing circuit. It has the function of receiving and imaging laser spots, and can receive and image the lasers emitted by cooperative targets; 3. Module S3, signal processing module. This module includes FPGA chip, serial communication chip and supporting circuits, etc. It can realize laser triggering program, direction finding receiving program and direction finding image processing program, and has the functions of signal processing, communication control and algorithm implementation for each submodule.

4. Module S4, search, capture and tracking module. This module has a two-dimensional posture rotation function and can adjust the posture according to the spot position information given by the signal processing module to achieve the alignment of the transmitting and receiving optical paths. The above modules work together to realize the cooperative laser direction finding function. First, the cooperative aircraft transmits laser signals to the cooperative target through the laser emission module; second, before the direction finding receiving module receives the laser spot, the signal processing module drives the search capture tracking module to search; then, after the direction finding receiving module receives the laser spot, the signal processing module uses the center extraction algorithm based on Gaussian fitting to solve the spot coordinates of the opponent's laser on the own direction finding sensor, thereby determining the opponent's direction information. The algorithm part includes the center extraction algorithm based on Gaussian fitting: The laser spot image can be divided into three parts according to the threshold value: the background of the image (area A), that is, the area outside the laser beam; the part with light intensity following Gaussian distribution but with noise (area B); the part with saturated grayscale value in the center of the laser spot (area C). First, extract area B as the sampling point, and solve the spot coordinates for this sampling point through the center extraction algorithm based on Gaussian fitting. The following matrix can be constructed from the sampling point coordinates: The following matrix can be constructed by the natural logarithm of the sampling point coordinates and the light intensity at the sampling point: The following vector can be obtained: Thus, the center coordinates of the laser spot can be obtained:

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