Window tracking method and system suitable for real-time tracking and measurement of small aerial targets

Abstract

The application provides a window tracking method and system suitable for real-time tracking and measurement of small targets in the air. The relative motion relationship between a measurement satellite and a small target in the air is calculated according to the dynamic data of the measurement satellite and the small target in the air within a measurement time, and the angular position change function of the target relative to the satellite measurement camera visual axis is solved. A suitable tracking window is designed within the field of view of the measurement camera. When the target moves out of the tracking window, the visual axis is quickly adjusted within a certain time, and when the visual axis adjustment is completed, the target is just moved to the center position of the field of view, and the visual axis is repeatedly kept-adjusted-kept to complete the window tracking of the cooperative target. The method is reasonable and easy to implement, and solves the problems of continuous adjustment of the tracking visual axis direction and large on-board calculation load when the measurement satellite and the target are moving at high speed in the air.

Description

Technical Field

[0001] This invention relates to the field of target tracking, and more specifically, to a window tracking method and system suitable for real-time tracking and measurement of small aerial targets. Background Technology

[0002] Tracking and measuring aerial targets using on-orbit optical measurement cameras typically employs two modes: autonomous tracking and programmed tracking. Autonomous tracking requires real-time on-orbit image processing to extract the target, obtain its deviation angle relative to the camera's optical axis, and feed this information back to the camera tracking servo system to guide the camera's optical axis towards the target. Its advantages include high flexibility and the target rarely leaving the field of view. However, it requires real-time on-orbit processing of measurement information, placing high demands on the onboard information processing system, making it suitable for non-cooperative target measurements. Programmed tracking requires designing a camera tracking program on the ground. Based on the target's and satellite's orbits and attitudes, the observation time and the camera's tracking program angle are determined and programmed onto the satellite. The program controls the camera's optical axis pointing, tracking and measuring the target. Its advantages include most data processing being completed on the ground, a lower load on the onboard information processing system, and ease of implementation, making it suitable for cooperative target measurements. Currently, there is no research on tracking methods for both the measurement satellite and the aerial target in real-time, high-speed motion, which to some extent limits the design of satellite measurement camera schemes.

[0003] The invention patent disclosed in patent document CN102538759B discloses a real-time fully automatic acquisition method for near-Earth and medium-high orbit air targets. This method measures air targets from the ground, with the ground telescope's position fixed and unchanged. It does not require real-time prediction of the target's spatial position and is not suitable for scenarios where both the target and the measuring satellite are moving.

[0004] Patent document CN102930558A discloses a multi-feature fusion infrared image target real-time tracking method, and patent document CN106485245A discloses an all-weather target real-time tracking method based on visible light and infrared images. These are image-based ground target tracking methods and are not suitable for tracking aerial targets that require real-time adjustment of the measuring camera's line of sight.

[0005] The method for detecting and identifying aerial targets using infrared imaging equipment disclosed in patent document CN102982333A is a method that uses a target contour extraction method and simultaneously utilizes multiple features of the target to identify the target. It is not suitable for identifying and tracking small targets with indistinct morphological features.

[0006] The method and apparatus for determining the trajectory of an aerial target disclosed in patent document CN102981160B is a technique that obtains preset radar measurement noise parameters and, at least based on the radar measurement noise parameters, obtains the detection points of the dynamic aerial target at different times based on the aerial target motion model. This technique is not suitable for satellite on-orbit tracking and measurement. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the purpose of this invention is to provide a window tracking method and system suitable for real-time tracking and measurement of small aerial targets.

[0008] A window tracking method for real-time tracking and measurement of small aerial targets, provided by the present invention, includes the following steps:

[0009] Spatial information prediction steps: Based on the orbital information of measuring satellites and small targets in the air, predict spatial information in real time;

[0010] Coordinate system transformation steps: Convert the position of the small aerial target into the camera measurement coordinate system;

[0011] Steps for calculating angular displacement: Calculate the angular displacement between the target's relative position vector and the measurement coordinate system;

[0012] Window tracking calculation steps: Fit the motion relationship curve of the small target in the air relative to the measuring satellite based on the calculated relative angular position time series, and realize window tracking based on the motion relationship curve.

[0013] Preferably, in the spatial information prediction step, the spatial position of the small aerial target is predicted in real time as ( ), speed is ( The spatial position of the satellite is ( ); ), speed is ( ).

[0014] Preferably, the coordinate system transformation step includes:

[0015] The steps for transforming the satellite orbit coordinate system are as follows: Transform the position of the small aerial target from the geocentric inertial frame to the satellite orbit coordinate system. The transformation matrix is... , ;

[0016] The steps for transforming the coordinate system of the measurement satellite are as follows: Transform the position of the small aerial target from the satellite orbit coordinate system to the measurement satellite coordinate system. The transformation matrix is: , ;

[0017] Camera measurement coordinate system transformation steps: Transform the position of the small aerial target from the satellite body coordinate system to the camera measurement coordinate system. The transformation matrix is ​​as follows: , ;

[0018] Summary steps: Transform the position of the small aerial target from the geocentric inertial frame to the camera measurement coordinate system. The transformation matrix is ​​as follows: , ;

[0019] Preferably, the relative coordinates of the small aerial target in the camera measurement coordinate system are calculated. )for

[0020] .

[0021] Preferably, the azimuth and elevation angles of the target's relative position vector relative to the measurement coordinate system are calculated as follows: , ,in:

[0022] .

[0023] Preferably, a motion relationship function of the target relative to the measuring satellite is fitted based on the calculated relative angular position time series. The camera's field of view is horizontal. ,vertical Number of pixels M×N, tracking window size is × ( After a single field-of-view adjustment, the angle between the target position and the center field of view is... , ( The quadrant in the field of view where the target is located is determined by the relative motion angle curve. The quadrant located in the quadrant with the smallest required motion angle along the line of view is used for window tracking, as follows:

[0024] ;

[0025] ;

[0026] ;

[0027] In this context, the subscript "out" indicates that the target has left the field of view window, "in" indicates that the target is in the initial position within the field of view, "hold" indicates that the line of sight / satellite is in the holding phase, and "move" indicates that the line of sight / satellite is in the adjustment phase; the subscripts "v" and "h" represent the vertical and horizontal directions, respectively; and the superscript "i" is the window number. Let be the time it takes for the target to move within the i-th field of view window. This is the time required for the line of sight / satellite to adjust from the i-th window to the (i+1)-th window, i.e., the time it takes for the target to move from the i-th field of view to the (i+1)-th field of view window.

[0028] Preferably, the motion relationship change function It is a quadratic polynomial function.

[0029] Preferably, the window tracking calculation step includes: setting and maintaining the center of the line of sight according to the angular position change curve of the target relative to the satellite; when the target moves out of the field of view window, quickly adjusting the line of sight within a certain period of time, so that when the line of sight adjustment ends, the target just moves to the center position of the field of view; and repeating the holding-adjusting-holding process to complete the window tracking of the cooperative target.

[0030] The window tracking system for real-time tracking and measurement of small aerial targets provided by the present invention includes the following modules:

[0031] Spatial Information Prediction Module: Predicts spatial information in real time based on the orbital information of measuring satellites and small targets in the air;

[0032] Coordinate system transformation module: Converts the position of small aerial targets into the camera measurement coordinate system;

[0033] Angular displacement calculation module: Calculates the angular displacement of the target's relative position vector relative to the measurement coordinate system;

[0034] Window tracking calculation module: Fits the motion relationship curve of the small target in the air relative to the measuring satellite based on the calculated relative angular position time series, and realizes window tracking based on the motion relationship curve.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1. This invention solves the problems of continuous adjustment of the tracking line of sight and high on-board computing load when both the measurement satellite and the target are moving at high speed in the air.

[0037] 2. This invention analyzes the relationship between the position and velocity of the aerial target and the measuring satellite, calculates the angular position change curve of the target relative to the satellite, establishes a window tracking algorithm, and uses step-by-step adjustment of the line of sight to keep the target within the field of view. It can achieve accurate tracking of aerial targets without the need for continuous adjustment of the line of sight.

[0038] 3. The method of the present invention is reasonable and easy to implement, and has a good effect on tracking moving targets in the air, with broad application prospects. Attached Figure Description

[0039] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0040] Figure 1 This is a schematic diagram of a window tracking method suitable for real-time tracking and measurement of small aerial targets.

[0041] Figure 2 This is a diagram showing the angular displacement relationship between the target and the line of sight relative to the measurement coordinate system.

[0042] Figure 3 This is a diagram illustrating the window tracking view axis adjustment process.

[0043] Figure 4 This is a diagram showing the relationship between the tracking window and the field of view.

[0044] Figure 5 This is a graph showing the results of window tracing. Detailed Implementation

[0045] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0046] like Figures 1 to 5 As shown, this invention discloses a window tracking method and system suitable for real-time tracking and measurement of small aerial targets. Based on the predicted dynamic data of the measurement satellite and the small aerial target within the measurement time, the relative motion relationship between the measurement satellite and the small aerial target is calculated, and the angular position change function of the target relative to the line of sight of the satellite measurement camera is solved. A suitable tracking window is designed within the field of view of the measurement camera. When the target moves out of the tracking window, the line of sight is rapidly adjusted within a certain time, so that when the line of sight adjustment ends, the target has just moved to the center position of the field of view. The line of sight is repeatedly held-adjusted-held to complete the window tracking of the cooperative target. Specifically, the following steps are included:

[0047] Step S1: Based on the orbital information of the measuring satellite and the small target in the air, predict its spatial position in real time. ), ( ) and speed ( ), ( ).

[0048] Step S2: Based on the result of step S1, transform the position of the small aerial target from the geocentric inertial frame to the measurement satellite's body coordinate system. The transformation matrix is: , (1) Step S3: Based on the result of step S1, transform the position of the small aerial target from the body coordinate system to the camera measurement coordinate system. The transformation matrix is ​​as follows: , (2)

[0049] Step S4: Based on the above results, transform the position of the small aerial target from the geocentric inertial frame to the camera measurement coordinate system. The transformation matrix is ​​as follows: , (3)

[0050] Step S5: Based on steps S1 and S4, determine the relative coordinates of the target in the camera measurement coordinate system. )for

[0051] (4)

[0052] Step S6: The angular displacement of the target's relative position vector relative to the measurement coordinate system is... , for

[0053] (5)

[0054] Step S7: Fit the motion relationship function of the target relative to the measuring satellite based on the calculated relative angular position time series. It is generally in the form of a quadratic polynomial, and the camera's field of view is horizontal. vertical Number of pixels M×N, tracking window size is × ( After a single field-of-view adjustment, the angle between the target position and the center field of view is... , ( The quadrant of the target's field of view is determined by the relative motion angle curve, and it lies in the quadrant where the required motion angle along the line of sight is minimal. The derived window tracking formula is as follows:

[0055] (6)

[0056] (7)

[0057] (8)

[0058] In the formula, the subscript "out" indicates that the target has left the field of view window, "in" indicates that the target is in the initial position within the field of view, "hold" indicates that the line of sight / satellite is in the holding phase, and "move" indicates that the line of sight / satellite is in the adjustment phase; the subscripts "v" and "h" represent the vertical and horizontal directions, respectively; and the superscript "i" is the window number. Let be the time it takes for the target to move within the i-th field of view window. This is the time required for the line of sight / satellite to adjust from the i-th window to the (i+1)-th window, i.e., the time it takes for the target to move from the i-th field of view to the (i+1)-th field of view window.

[0059] The orbital parameters for the design measurement satellite and air targets are shown in Table 1.

[0060] Table 1. Orbital parameters of the measured satellite and target

[0061]

[0062] Based on the orbital parameters, the positions and velocities of the measuring satellite and the aerial target are calculated. Following steps (1) to (5) of the invention, the angular displacement between the target's relative position vector and the measuring coordinate system is calculated. , As attached Figure 2 .

[0063] Based on the target's angular position change curve relative to the satellite, the line-of-sight (LOS) center is set and maintained. When the target moves out of the field of view window, the LOS point is rapidly adjusted within a certain time, ensuring that the target moves back to the center of the field of view just as the adjustment ends. This hold-adjust-hold process is repeated to complete window tracking of the cooperative target. (See attached image) Figure 3 .

[0064] Based on the fitted motion curve of the aerial target relative to the measuring satellite, the tracking window is designed as shown in the attached figure. Figure 4 As shown.

[0065] Based on the window tracking formulas (6), (7), and (8) and the designed tracking window, the angle at which the view axis moves from the i-th window to the (i+1)-th window is: , The average angular velocity in both directions is , ,make . This is the time adjustment factor; the subscript g indicates the line of sight / satellite.

[0066] (9)

[0067] (10)

[0068] When the view is held in the i-th window, the angle of the view axis relative to its zero position is: ,

[0069] (“ "for (11)

[0070] (“ "for (12)

[0071] Percentage of adjacent field of view coverage is ,

[0072] (13)

[0073] (14)

[0074] In this implementation, the camera's horizontal field of view is 4.4. o Vertical field of view 5.5 o n1=1 / 3, n2=0.

[0075] Based on the functional relationship between the line-of-sight angle change and time obtained from the fitting, and combined with formulas (6) to (12), window tracking of aerial targets is achieved. The tracking results are shown in the appendix. Figure 5 The black dot represents the target, the black box represents the tracking window, and the black line represents the fitted curves for pitch and roll angles. During the 507-second tracking process:

[0076] (1) The visual axis was adjusted 11 times.

[0077] (2) Range of angular velocity for line of sight adjustment

[0078] Pitch: 0.00469852~2.25734 (° / s)

[0079] Rolling speed: 0.216202~4.81349 (° / s)

[0080] (3) Field of view coverage percentage (%)

[0081] Pitch: 22.542%

[0082] Rolling: 89.407%

[0083] The results show that the present invention achieves the goal of keeping the aerial target always within the tracking field of view without frequent adjustments to the line of sight, even when both the target and the measuring satellite are moving at high speed in real time throughout the entire tracking process.

[0084] The window tracking system for real-time tracking and measurement of small aerial targets provided by the present invention includes a spatial information prediction module: predicting spatial information in real time based on the orbital information of the measuring satellite and the small aerial target; a coordinate system transformation module: converting the position of the small aerial target into the camera measurement coordinate system; an angular displacement calculation module: calculating the angular displacement between the target's relative position vector and the measurement coordinate system; and a window tracking calculation module: fitting the motion relationship curve of the small aerial target relative to the measuring satellite based on the calculated relative angular position time series, and realizing window tracking based on the motion relationship curve.

[0085] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A window tracking method suitable for real-time tracking and measurement of small aerial targets, characterized in that, Includes the following steps: Spatial information prediction steps: Based on the orbital information of measuring satellites and small targets in the air, predict spatial information in real time; Coordinate system transformation steps: Convert the position of the small aerial target into the camera measurement coordinate system; Steps for calculating angular displacement: Calculate the angular displacement between the target's relative position vector and the measurement coordinate system; Window tracking calculation steps: Fit the motion relationship curve of the small aerial target relative to the measuring satellite based on the calculated relative angular position time series, and realize window tracking based on the motion relationship curve; In the spatial information prediction step, the spatial position of the small aerial target is predicted in real time as ( ), speed is ( The spatial position of the satellite is ( ); ), speed is ( ); The coordinate system transformation steps include: The steps for transforming the satellite orbit coordinate system are as follows: Transform the position of the small aerial target from the geocentric inertial frame to the satellite orbit coordinate system. The transformation matrix is... , ; The steps for transforming the coordinate system of the measurement satellite are as follows: Transform the position of the small aerial target from the satellite orbit coordinate system to the measurement satellite coordinate system. The transformation matrix is: , ; Camera measurement coordinate system transformation steps: Transform the position of the small aerial target from the satellite body coordinate system to the camera measurement coordinate system. The transformation matrix is ​​as follows: , ; Summary steps: Transform the position of the small aerial target from the geocentric inertial frame to the camera measurement coordinate system. The transformation matrix is ​​as follows: , ; Where R, j, and u are right ascension, orbital inclination, and right ascension of the ascending node, respectively. γ and Ψ are satellite attitude angles, β and θ are the pitch and azimuth angles of the tilting mirror, and M1, M2 and M3 are rotation matrices; Calculate the relative coordinates of the small aerial target in the camera measurement coordinate system. )for ； The relative position vector of the target and the azimuth and elevation angles of the measurement coordinate system are calculated as follows: , ,in: ； The motion relationship function between the target and the measuring satellite was fitted based on the calculated relative angular position time series. The camera's field of view is horizontal. ,vertical Number of pixels M×N, tracking window size is × , After a single field-of-view adjustment, the angle between the target position and the center of the field of view is... , , The quadrant in the field of view where the target is located is determined by the relative motion angle curve. The quadrant located in the quadrant with the smallest required motion angle along the line of view is used for window tracking, as follows: ； ； ； Wherein, the subscript "out" indicates that the target has left the field of view window, "in" indicates that the target is in the initial position within the field of view, "hold" indicates that the line of sight / satellite is in the holding phase, and "move" indicates that the line of sight / satellite is in the adjustment phase; the subscripts "v" and "h" represent the vertical and horizontal directions, respectively; and the superscript "i" is the window number. Let be the time it takes for the target to move within the i-th field of view window. This is the time required for the line of sight / satellite to adjust from the i-th window to the (i+1)-th window, i.e., the time it takes for the target to move from the i-th field of view to the (i+1)-th field of view window.

2. The window tracking method for real-time tracking and measurement of small aerial targets according to claim 1, characterized in that, The motion relationship change function It is a quadratic polynomial function.

3. The window tracking method for real-time tracking and measurement of small aerial targets according to claim 1, characterized in that, The window tracking calculation steps include: setting and maintaining the center of the line of sight based on the angular position change curve of the target relative to the satellite; when the target moves out of the field of view window, quickly adjusting the line of sight within a certain time, so that when the line of sight adjustment ends, the target just moves to the center of the field of view; and repeating the hold-adjust-hold process to complete the window tracking of the cooperative target.

4. A window tracking system suitable for real-time tracking and measurement of small aerial targets, characterized in that, Includes the following modules: Spatial Information Prediction Module: Predicts spatial information in real time based on the orbital information of measuring satellites and small targets in the air; Coordinate system transformation module: Converts the position of small aerial targets into the camera measurement coordinate system; Angular displacement calculation module: Calculates the angular displacement of the target's relative position vector relative to the measurement coordinate system; Window tracking calculation module: Fits the motion relationship curve of the small aerial target relative to the measuring satellite based on the calculated relative angle position time series, and realizes window tracking based on the motion relationship curve; In the spatial information prediction module, the spatial location of small aerial targets is predicted in real time as ( ), speed is ( The spatial position of the satellite is ( ); ), speed is ( ); The coordinate system transformation module includes: Satellite orbit coordinate system transformation: The position of a small aerial target is transformed from the geocentric inertial frame to the satellite orbit coordinate system. The transformation matrix is ​​as follows: , ; Satellite body coordinate system transformation: The position of the small aerial target is transformed from the satellite orbit coordinate system to the satellite body coordinate system. The transformation matrix is ​​as follows: , ; Camera measurement coordinate system transformation: The position of a small aerial target is transformed from the satellite body coordinate system to the camera measurement coordinate system. The transformation matrix is ​​as follows: , ; Summary: The position of a small aerial target is transformed from the geocentric inertial frame to the camera measurement coordinate system. The transformation matrix is ​​as follows: , ; Where R, j, and u are right ascension, orbital inclination, and right ascension of the ascending node, respectively. γ and Ψ are satellite attitude angles, β and θ are the pitch and azimuth angles of the tilting mirror, and M1, M2 and M3 are rotation matrices; Calculate the relative coordinates of the small aerial target in the camera measurement coordinate system. )for ； The relative position vector of the target and the azimuth and elevation angles of the measurement coordinate system are calculated as follows: , ,in: ； The motion relationship function between the target and the measuring satellite was fitted based on the calculated relative angular position time series. The camera's field of view is horizontal. ,vertical Number of pixels M×N, tracking window size is × , After a single field-of-view adjustment, the angle between the target position and the center of the field of view is... , , The quadrant in the field of view where the target is located is determined by the relative motion angle curve. The quadrant located in the quadrant with the smallest required motion angle along the line of view is used for window tracking, as follows: ； ； ； Wherein, the subscript "out" indicates that the target has left the field of view window, "in" indicates that the target is in the initial position within the field of view, "hold" indicates that the line of sight / satellite is in the holding phase, and "move" indicates that the line of sight / satellite is in the adjustment phase; the subscripts "v" and "h" represent the vertical and horizontal directions, respectively; and the superscript "i" is the window number. Let be the time it takes for the target to move within the i-th field of view window. This is the time required for the line of sight / satellite to adjust from the i-th window to the (i+1)-th window, i.e., the time it takes for the target to move from the i-th field of view to the (i+1)-th field of view window.

Images