Satellite-ground laser communication initial acquisition method

Abstract

The invention discloses a satellite-to-ground laser communication initial capturing method, relates to the field of satellite-to-ground laser communication, and solves the problems that in the existing satellite-to-ground laser communication link establishment process, due to the fact that an interference light source is misjudged as beacon light under the interference of complex ground background light, the link establishment process is limited and the like. Aiming at an initial capture scene of satellite-ground laser communication, a special beacon light distribution graph is designed at a ground end, the beacon light distribution graph is shot during initial capture of an on-satellite laser communication terminal, and the position of the beacon light is quickly and accurately positioned in a complex ground light interference environment through a special recognition algorithm, so that the link establishment time is shortened. According to the method, the influence of ground stray light on the beacon light positioning process can be eliminated, initial capture is completed quickly and accurately, and the method has certain universality and expansibility and can be applied to the link establishment process of satellite-ground laser communication.

Description

Technical Field

[0001] The invention relates to the field of satellite-to-ground laser communication, and in particular to an initial capture method for satellite-to-ground laser communication. Background Art

[0002] Wireless optical communication is one of the important means to realize air-based, space-based, ground-based communication links. It has broad development prospects due to its advantages such as good security and high bandwidth. With the development of commercial aerospace, the demand for downlink data transmission resources of satellites is increasing, which in turn promotes the development and application of satellite-to-ground laser communication technology.

[0003] During satellite-to-ground laser communication, the stable link establishment communication time between low-orbit satellites and laser ground stations is relatively short, generally about 10 minutes. Moreover, when the laser ground station is at a low elevation angle, it is affected by atmospheric turbulence and cannot establish a stable link. Therefore, the effective communication window time is even shorter. Therefore, it is particularly important to quickly and accurately complete the link establishment and ensure sufficient communication time.

[0004] The link establishment process of satellite-to-ground laser communication includes initial pointing, initial capture, coarse tracking, and fine tracking. In the initial capture and coarse tracking stages, the beacon light is positioned by extracting the centroid of the beacon light. Commonly used methods include the centroid algorithm, the centroid algorithm, and the least squares-based circle fitting algorithm. However, these algorithms are easily misjudged as beacon light under the interference of complex ground background light, which leads to link establishment failure, so there are certain limitations. Summary of the invention

[0005] The present invention provides a satellite-to-ground laser communication initial capture method to solve the problem that in the existing satellite-to-ground laser communication link establishment process, an interfering light source is misjudged as a beacon light under the interference of complex ground background light, resulting in limitations in the link establishment process.

[0006] A satellite-to-ground laser communication initial acquisition method comprises the following steps:

[0007] Step 1: Deploy the beacon light distribution pattern with the laser ground station as the center and design the ground beacon light;

[0008] Step 2: photographing the ground beacon light using an onboard laser communication terminal camera to obtain image data of the ground beacon light;

[0009] Step 3: extracting the centroid of the light spot in the image data in step 2, and using the centroid of the light spot for matching and identification according to the distribution characteristics of the ground beacon light;

[0010] Step 4: Determine the beacon light position of the laser ground station.

[0011] Furthermore, in step 1, the characteristics of the deployed beacon light distribution pattern are specifically:

[0012] Nine beacon lights are arranged on two non-perpendicular intersecting straight lines, with the position of the laser ground station beacon light as the intersection point. On each straight line, two beacon lights are set on both sides of the center with the intersection point as the center.

[0013] Furthermore, the beacon light arrangement interval matches the onboard laser communication terminal camera parameters, that is, the image points of the nine beacon lights occupy half of the image area.

[0014] Furthermore, in step 3, the specific process of matching and identification is as follows:

[0015] Step 31: From the spot mass center {P1, P2, ..., P k …,P n}Select five points;

[0016] Step 3.2: Fit the five selected points to a straight line, and the fitting degree R 2 If the value is greater than the threshold ε, the five points are considered to form a straight line, and finally m straight lines {L1, L2, ..., L m};

[0017] Step 3. From m straight lines {L1, L2, ..., L m}Select any two straight lines {L i ,L j}; where 1≤i, j≤m;

[0018] Step 34: Calculate the two selected straight lines {L i ,L j}The intersection coordinates P ij , and calculate the intersection coordinates P ij The distance to the centroid of all light spots {d ij1 ,d ij2 ,…,d ijk ,…,d ijn}, 1≤k≤n; if there is a spot centroid P k With the intersection coordinates P ij The distance d ijk Less than the distance threshold δ, and the spot centroid P k To form a straight line L i , L j The light spot is on the straight line L i , L j P k If there are two light spots on each side of the light spot, the matching is successful, otherwise the matching fails.

[0019] Furthermore, the position of the laser ground station beacon light in step 4 is the spot centroid P k The coordinates of the point.

[0020] Beneficial effects of the present invention: The capture method described in the present invention can eliminate the interference of ground stray light on the beacon light positioning process, quickly and accurately determine the position of the beacon light, and shorten the link establishment time; the method of the present invention does not require special library function support, has a small amount of calculation, occupies few resources, and has high real-time performance; the method of the present invention is highly flexible and can modify the number of beacon lights and the straight line angle according to the ground station environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A schematic diagram of the distribution of beacon light of a laser ground station in a satellite-to-ground laser communication initial capture method according to the present invention;

[0022] Figure 2 It is a schematic diagram of the centroid distribution of the ground beacon light image spot;

[0023] Figure 3 Schematic diagram of the centroid distribution of the light spot of the image without ground beacon. DETAILED DESCRIPTION

[0024] Combination Figures 1 to 3 This embodiment describes a method for initial capture of satellite-to-ground laser communications, in which a beacon light distribution pattern is deployed with a laser ground station as the center. When the onboard laser communication terminal initially captures the ground beacon light, it takes an image of the ground beacon light, extracts the centroid of the light spot in the image, and then performs feature matching to quickly and accurately identify the position of the ground station beacon light.

[0025] The specific process of the satellite-to-ground laser communication initial acquisition method described in this embodiment is as follows:

[0026] 1. Design a beacon light distribution pattern on the ground; the beacon light distribution pattern includes the beacon light of the laser ground station.

[0027] The characteristics of the beacon light distribution pattern are as follows: it contains 9 beacon light signals, and the 9 beacon lights are arranged on two non-perpendicular straight lines, wherein the position of the laser ground station beacon light is used as the intersection point, and on each straight line, with the intersection point as the center, two beacon lights are arranged on both sides of the center.

[0028] 2. The onboard laser communication terminal camera captures the ground beacon light and obtains image data;

[0029] The beacon light arrangement interval matches the onboard laser communication terminal camera, that is, the beacon light arrangement interval must ensure that the image points of adjacent beacon lights do not overlap, and the distribution of the 9 image points should occupy more than half of the image area as much as possible.

[0030] 3. Extract the centroid of the light spot in the image data, denoted as {P1,P2,…,P k …,P n};

[0031] 4. According to the distribution characteristics of the beacon light, the centroid of the light spot is used for matching and identification;

[0032] The matching identification method is as follows:

[0033] 1) From the spot centroid {P1,P2,…,P k …,P n}Select 5 points in total Selection method:

[0034] 2) Fit the selected 5 points to a straight line, and the fitting degree R 2 If it is greater than the threshold ε, then it is considered that these five points form a straight line. There are m straight lines {L1,L2,…,L m};

[0035] 3) From m straight lines {L1,L2,…,L m}Select any two straight lines {L i ,L j}, where 1≤i, j≤m; Selection method:

[0036] 4) Calculate the two selected straight lines {L i ,L j}The intersection coordinates P ij , calculate P ij The distance to the centroid of all light spots {d ij1 ,d ij2 ,…,d ijk ,…,d ijn}, 1≤k≤n; if there is a spot centroid P k With P ij The distance d ijk is less than the threshold δ, and P k To form a straight line L i , L j The light spot is on the straight line L i , L j P k If there are two light spots on each side of the light spot, the matching is successful, otherwise the matching fails.

[0037] In the above matching and recognition method, the spot centroid P k The coordinates of the point are the coordinates of the beacon light of the laser ground station.

[0038] 5. Confirm the beacon light position of the laser ground station.

[0039] like Figure 1As shown, in this embodiment, it is first necessary to deploy the beacon light distribution pattern with the laser ground station as the center. With the laser ground station beacon light as the center, the ground station beacon light and four beacon lights are arranged in a straight line, and the ground station beacon light is in the middle, with two beacon lights on each side; the ground station beacon light and the other four beacon lights are arranged in another straight line, and the ground station beacon light is in the middle, with two beacon lights on each side. Figure 1 The distance between two adjacent beacon lights on each straight line must match the parameters of the onboard laser communication terminal camera. For example, if the camera resolution is 1m and the diffuse spot size of the beacon light imaging is 3×3 pixels, in order to avoid overlapping of two light spots in the image, the center interval of the two light spots can be set to 10 pixels, that is, the two beacon light sources on the same straight line need to be 10m apart. Figure 1 The two straight lines are not perpendicular, which is convenient for subsequent straight line fitting and intersection coordinate calculation. The interval between the two beacon lights and the angle between the two straight lines can be adjusted according to the actual imaging effect and the size of the laser ground station site to achieve convenient deployment and clear image spots.

[0040] like Figure 2 As shown in the figure, if the onboard laser communication terminal camera captures the beacon light of the ground station, the process of matching and identifying the image is as follows:

[0041] 1. Extract the centroid of the light spot in the image, and obtain 13 points in total, namely a, b, c, d, e, f, g, h, i, j, k, l, and m;

[0042] 2. Select 5 points to fit the straight line. A selection method, where points a, b, c, d, and e can be fitted into a straight line L1, points f, g, c, h, and i can be fitted into a straight line L2, and points j, g, k, e, and l can be fitted into a straight line L3. The combination of other points cannot be fitted into a straight line.

[0043] 3. Select 2 straight lines to calculate the coordinates of the intersection. There are three selection methods. The following three cases are analyzed: The intersection of L1 and L2 is P 12 , P 12 The distance from the midpoint c of the 13 light spot centroids is less than the threshold value. Point c is a point that forms straight lines L1 and L2. There are two points a, b and d, e on both sides of the midpoint c of straight line L1, and there are two points f, g and h, i on both sides of the midpoint c of straight line L2. Therefore, point c can be determined to be the beacon light position of the laser ground station; the intersection of L1 and L3 is P 13 , P 13The distance from the midpoint e of the 13 light spot centroids is less than the threshold. Point e is a point that forms straight lines L1 and L3. There are 4 points a, b, d, e and 0 on both sides of the midpoint e of straight line L1, and there are 3 points j, g, k and 1 point l on both sides of the midpoint e of straight line L3. Therefore, point e is not the beacon light of the laser ground station; the intersection of L2 and L3 is P 23 , P 23 The distance from the midpoint g in the centroid of the 13 light spots is less than the threshold. Point g is a point that constitutes straight lines L2 and L3. There are three points c, h, i and one point f on both sides of the midpoint g in straight line L2, and there are three points k, e, l and one point j on both sides of the midpoint g in straight line L3. Therefore, point g is not the beacon light of the laser ground station.

[0044] Through the above method, it can be determined that point c is the beacon light position of the laser ground station.

[0045] like Figure 3 As shown in the figure, if the onboard laser communication terminal camera does not capture the beacon light of the ground station, the process of matching and identifying the image is as follows:

[0046] 1. Extract the centroid of the light spot in the image and obtain 10 points in total, namely a, b, c, d, e, f, g, h, i, and j;

[0047] 2. Select 5 points to fit the straight line. There are two selection methods, and all combinations cannot be fitted into a straight line;

[0048] Through the above method, it can be determined that there is no laser ground station beacon light in the image.

[0049] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0050] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A satellite-to-ground laser communication initial acquisition method, characterized by: The capture method is implemented by the following steps: Step 1: Deploy the beacon light distribution pattern with the laser ground station as the center and design the ground beacon light; Step 2: photographing the ground beacon light using an onboard laser communication terminal camera to obtain image data of the ground beacon light; Step 3: extracting the centroid of the light spot in the image data in step 2, and using the centroid of the light spot for matching and identification according to the distribution characteristics of the ground beacon light; Step 4: Determine the beacon light position of the laser ground station.

2. The satellite-to-ground laser communication initial acquisition method according to claim 1, characterized in that: In step 1, the characteristics of the deployed beacon light distribution pattern are specifically: Nine beacon lights are arranged on two non-perpendicular intersecting straight lines, with the position of the laser ground station beacon light as the intersection point. On each straight line, two beacon lights are set on both sides of the center with the intersection point as the center.

3. The satellite-to-ground laser communication initial acquisition method according to claim 1, characterized in that: The beacon light arrangement interval matches the on-board laser communication terminal camera parameters, that is, the image points of the nine beacon lights occupy half of the image area.

4. The satellite-to-ground laser communication initial acquisition method according to claim 1, characterized in that: In step 3, the specific process of matching and identification is as follows: Step 31: From the spot mass center {P1, P2, ..., P k …,P n }Select five points; Step 3.2: Fit the five selected points to a straight line, and the fitting degree R 2 If the value is greater than the threshold ε, the five points are considered to form a straight line, and finally m straight lines {L1, L2, ..., L m }; Step 3. From m straight lines {L1, L2, ..., L m }Select any two straight lines {L i ,L j }; where 1≤i, j≤m; Step 34: Calculate the two selected straight lines {L i ,L j }The intersection coordinates P ij , and calculate the intersection coordinates P ij The distance to the centroid of all light spots {d ij1 ,d ij2 ,…,d ijk ,…,d ijn }, 1≤k≤n; if there is a spot centroid P k With the intersection coordinates P ij The distance d ijk Less than the distance threshold δ, and the spot centroid P k To form a straight line L i , L j The light spot is on the straight line L i , L j P k If there are two light spots on each side of the light spot, the matching is successful, otherwise the matching fails.

5. The satellite-to-ground laser communication initial acquisition method according to claim 1, characterized in that: The position of the laser ground station beacon light in step 4 is the spot centroid P k The coordinates of the point.

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