CN112505795A - Photoelectric detection system and method for GEO satellite omnidirectional alarm - Google Patents

Photoelectric detection system and method for GEO satellite omnidirectional alarm Download PDF

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CN112505795A
CN112505795A CN202011119611.XA CN202011119611A CN112505795A CN 112505795 A CN112505795 A CN 112505795A CN 202011119611 A CN202011119611 A CN 202011119611A CN 112505795 A CN112505795 A CN 112505795A
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visible light
camera
geo
satellite
geo satellite
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CN112505795B (en
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李建华
李志峰
薛峰
赵茜
蔡雯琳
薛莲
牛振红
杜润乐
束逸
张力
刘佳琪
刘鑫
赵巨岩
刘洪艳
高路
彭程远
艾夏
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Beijing Aerospace Changzheng Aircraft Institute
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Beijing Aerospace Changzheng Aircraft Institute
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V8/00—Prospecting or detecting by optical means
    • G01V8/10—Detecting, e.g. by using light barriers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
    • H04N23/60—Control of cameras or camera modules
    • H04N23/695—Control of camera direction for changing a field of view, e.g. pan, tilt or based on tracking of objects
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
    • H04N23/70—Circuitry for compensating brightness variation in the scene
    • H04N23/73—Circuitry for compensating brightness variation in the scene by influencing the exposure time
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
    • H04N23/90—Arrangement of cameras or camera modules, e.g. multiple cameras in TV studios or sports stadiums
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy

Abstract

A photoelectric detection system and method for GEO satellite omnidirectional alarm belongs to the technical field of omnidirectional alarm, wherein a GEO satellite is equivalent to a cuboid, four turntables are respectively arranged on four edges perpendicular to a GEO orbital plane on the GEO satellite, a visible light camera is arranged on each turntable, and the other two cameras are directly arranged on two planes parallel to the GEO orbital plane; the four turntables control the four visible light cameras in the GEO orbital plane to avoid direct sunlight according to the position and angle relation between the GEO satellite and the sun, ensure that the four visible light cameras are not shielded by the satellite, and simultaneously cover a space area except a sun avoiding angle; installing at least one solar blind ultraviolet camera on the GEO satellite, and keeping the view field of the ultraviolet camera to cover the earth all the time; and judging whether a target needing to be warned exists or not according to the optical images acquired by the six visible light cameras and the ultraviolet image acquired by the at least one ultraviolet camera.

Description

Photoelectric detection system and method for GEO satellite omnidirectional alarm
Technical Field
The invention relates to a photoelectric detection system and a method for omnidirectional alarm of a GEO satellite, belonging to the technical field of omnidirectional alarm.
Background
The GEO satellite is generally a high-value satellite, and the safe operation significance of the GEO satellite is great. Currently, GEO satellites face a major threat of space fragmentation.
With the increasing space activities of human beings exploring space, the space debris environment is increasingly severe. Although the space debris is mostly small in size, with many debris in the centimeter and millimeter scale, it has a surprising destructive power. The great destructive power of the space debris comes from the speed of the space debris, the average relative speed of the space debris when the space debris collides with a spacecraft reaches thousands of meters per second, the collision kinetic energy is very great, once the space debris collides with a satellite, the satellite can be slightly perforated and damaged, and the satellite can be completely failed or even catastrophically disassembled.
Because the fragments have small volume and too many quantity, the orbits of the fragments cannot be measured one by one, the spacecraft cannot implement a maneuvering strategy to avoid collision, and only the spacecraft can be protected to improve the immunity. In order to avoid the collision of the space debris by the spacecraft, the collision threat warning of the space debris must be completed.
The existing satellite omnidirectional alarm technology has the following problems to be solved:
1) large alarm view field
2) Long detection distance
3) Small target size
4) There is interference of solar radiation with the earth background
5) The volume, weight and power consumption are limited
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the method comprises the steps of enabling a GEO satellite to be equivalent to a cuboid, respectively installing four turntables on four edges perpendicular to a GEO orbital plane on the GEO satellite, installing a visible light camera on each turntable, and directly installing the other two cameras on two planes parallel to the GEO orbital plane; the visual fields of the four cameras on the four turntables and the two cameras on the upper and lower surfaces of the four cameras basically cover 360-degree stereoscopic space around the GEO satellite; the four turntables control the four visible light cameras in the GEO orbital plane to avoid direct sunlight according to the position and angle relation between the GEO satellite and the sun, ensure that the four visible light cameras are not shielded by the satellite, and simultaneously cover a space area except a sun avoiding angle; installing at least one solar blind ultraviolet camera on the GEO satellite, and keeping the view field of the ultraviolet camera to cover the earth all the time; and judging whether a target needing to be warned exists or not according to the optical images acquired by the six visible light cameras and the ultraviolet image acquired by the at least one ultraviolet camera.
The purpose of the invention is realized by the following technical scheme:
a photoelectric detection system for omnidirectional GEO satellite alarm comprises an image processing module, four turntables, six visible light cameras and a solar blind ultraviolet camera;
the GEO satellite is equivalent to a cuboid, four turntables are respectively arranged on four edges perpendicular to a GEO orbital plane on the GEO satellite, each turntable is provided with a visible light camera, and the other two visible light cameras are directly arranged on two surfaces parallel to the GEO orbital plane; the fields of view of the six visible light cameras cover 360-degree stereoscopic space around the GEO satellite to the maximum extent;
the four turntables control the four visible light cameras to avoid direct sunlight according to the position and angle relation between the GEO satellite and the sun;
the solar blind ultraviolet camera is arranged on the GEO satellite, and the view field of the solar blind ultraviolet camera is kept to cover the earth all the time;
the image processing module judges whether a target needing warning exists according to an optical image acquired by the visible light camera and an ultraviolet image acquired by the solar blind ultraviolet camera.
The above photoelectric detection system for GEO satellite omnidirectional warning preferably has a half field angle of 50 ° for each visible light camera.
According to the photoelectric detection system for the GEO satellite omnidirectional alarm, the optical detector is preferably selected according to the half-field angle, the detection distance and the target characteristic of each visible light camera, and the sensitivity of the optical detector reaches 5 stars and above.
Preferably, when the target needing to be warned is judged to exist, the photoelectric detection system for omnidirectional warning of the GEO satellite rejects the star points and the image noise points in the optical image according to the fact that whether the detected target moves.
Preferably, when judging whether the target needing to be alarmed exists, the photoelectric detection system for omnidirectional alarming of the GEO satellite improves the detection probability and the acting distance of the visible light camera by using a method for increasing the exposure time.
Preferably, in the photoelectric detection system for omnidirectional GEO satellite alarm, when the turntable is used for controlling the visible light camera to avoid direct sunlight, the maximum sun avoiding angular field of view is 34 °.
Preferably, in the photoelectric detection system for omnidirectional GEO satellite alarm, the optical system of the solar blind ultraviolet camera has a field of view of 18 ° x 18 °.
The photoelectric detection system for the GEO satellite omnidirectional alarm preferably utilizes the turntable angle adjustment function, so that the included angle between the pointing direction of the upper edge of the visual field of the visible light camera and the sun or the included angle between the pointing direction of the lower edge of the visual field of the visible light camera and the sun is always kept unchanged, and meanwhile, the satellite body does not shield the other edge of the visual field of the camera, namely, the upper edge and the lower edge of the visual field of the visible light camera are limited by the sun ray direction and the surface of the satellite body.
Preferably, for any visible light camera located on an edge, the photoelectric detection system changes with the positions and angles of the satellites and the sun, and when the included angle between the edge of the visual field of one camera, which is pointed by the optical axis of the visible light camera, and the surface of an adjacent satellite is smaller than 1 degree, the pointing direction of the optical axis of the visible light camera is adjusted, so that the included angle between the edge of the visual field of the camera and the incident direction of the sun is the sun avoidance angle.
Preferably, the turntable is a one-dimensional turntable, and the adjustment direction of the turntable is parallel to the GEO orbital plane.
Preferably, in the above photoelectric detection system for omni-directional GEO satellite alarm, when determining whether there is a target to be alarmed, the system determines that the detected target is close to the satellite when the gray scale of the detected target is 4 times or more of the gray scale of the detected target at the moment of discovery.
Preferably, the photoelectric detection system for the omnidirectional GEO satellite alarm confirms the moving target by utilizing the trailing phenomenon of the long-time exposure moving target, and directly eliminates the star point target through star map identification.
A photoelectric detection method for omnidirectional GEO satellite alarm comprises the following steps:
s1, enabling the GEO satellite to be equivalent to a cuboid, and respectively installing four visible light cameras on four edges, perpendicular to the GEO orbital plane, of the GEO satellite; installing two visible light cameras on two surfaces parallel to the GEO orbital plane; the fields of view of the six visible light cameras cover 360-degree stereoscopic space around the GEO satellite to the maximum extent;
s2, controlling four visible light cameras on the edge to avoid direct sunlight according to the position and angle relation between the GEO satellite and the sun;
s3, installing at least one solar blind ultraviolet camera on the GEO satellite, and keeping the view field of the solar blind ultraviolet camera to cover the earth all the time;
and S4, judging whether a target needing to be warned exists according to the optical images acquired by the six visible light cameras and the ultraviolet image acquired by the at least one solar blind ultraviolet camera.
Compared with the prior art, the invention has the following beneficial effects:
(1) the characteristics that GEO orbit space fragments are irradiated by the sun are fully utilized, a plurality of large-view-field visible light cameras are adopted for passive detection, and compared with active detection such as microwave or laser radar, the size, the weight and the power consumption of the system are reduced to the maximum extent.
(2) Aiming at the problem that the normal work of a visible light camera is influenced due to the fact that the sun incident angle is constantly changed due to the orbital motion of a satellite, the camera is provided with an angle adjusting rotary table, an optimal pointing area is automatically calculated, sunlight can be prevented from directly entering a view field, normal imaging is interfered, meanwhile, the imaging of the camera is prevented from being shielded by a satellite body, and the coverage rate of the whole space is larger than 90%.
(3) In order to avoid the influence of sunlight reflected by the earth on the visible light camera, the solar blind ultraviolet camera is equipped to always point to the earth area, the vacancy of partial visual field alarm is filled, the atmospheric absorption of the solar blind ultraviolet earth is obvious, the background of an image is reduced to the maximum extent, and compared with an infrared detection scheme of an atmospheric absorption waveband, the volume, the weight and the acting distance of the scheme are greatly improved;
(4) the ultra-large area array visible light detector is adopted, when the large-field-of-view detection is carried out, the large-field-of-view detection has a large entrance pupil size, the sensitivity of the system is easy to guarantee, and a large action distance can be achieved;
(5) by adopting the large-field staring detection imaging scheme, the bearing service life problem faced by the high-speed scanning of the turntable can be avoided compared with the omnidirectional scanning aspect.
(6) Different from the traditional detection system exposure time setting method which generally avoids the occurrence of motion tailing, the scheme adopts long exposure time aiming at the deep space background, on one hand, target signals are accumulated, the action distance of the detection system is increased, on the other hand, the motion tailing phenomenon of the target is detected, and the moving target and the static target are conveniently distinguished.
(7) Compared with the scanning scheme, the technical scheme of the invention has the advantages that the self platform stability is good, the image detection is easier to detect the moving target, and the self motion decoupling requirement is avoided.
(8) The most marginal position of the satellite, such as the edge, is selected as the installation position of the visible light camera, so that the constraint of the satellite body on the observation field of view is reduced to the maximum extent, and all space regions except the sun avoidance angle can be covered.
(9) The technology of the invention defines that the size of a visible light field is 100 degrees multiplied by 100 degrees, the maximum sun avoiding angle which can be realized for a hexahedral satellite is 32 degrees, and the coverage rate of the whole alarm space is more than 90 percent.
(10) If the satellite is a cylinder, the related scheme is similar to a hexahedron, the size of the view field is similar to the index of the evasion angle, and the scheme has good adaptability.
(11) The pointing adjustment scheme is not affected by seasons, and the one-dimensional turntable can be adjusted in a single direction, so that the complexity caused by using two dimensions is avoided.
Drawings
FIG. 1 is a schematic diagram of the continuous adjustment of a visible light camera with the operation of a satellite;
FIG. 2 is a schematic diagram of a 100 by 100 wide-angle field of view optical system;
FIG. 3 is a schematic diagram of a maximum value of the avoidance angle of 34 deg. calculation;
fig. 4 is a schematic diagram of the camera pointing wide range adjustment. When the incident direction of the sun passes through the plane 4 bisector of the plane 3, the direction of the optical axis of the camera needs to be adjusted up and down to avoid the plane 3 from blocking the view field, and the direction is adjusted from the lower direction of the figure 2 to the upper direction of the figure;
FIG. 5 is a schematic diagram showing the meaning of the sun phase angle θ, showing the angle between the optical axis direction vector and the target to sun direction vector;
FIG. 6 shows a cross section of 0.25m, excluding 400km2A relation graph of target star and the like of the reflection section and the sun phase angle;
fig. 7 is an influence of seasonal variation on the avoidance angle.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
A photoelectric detection system for omnidirectional GEO satellite alarm comprises an image processing module, four one-dimensional turntables, six visible light cameras and a solar blind ultraviolet camera;
the GEO satellite is equivalent to a cuboid, four turntables are respectively arranged on four edges perpendicular to a GEO orbital plane on the GEO satellite, each turntable is provided with a visible light camera, and the other two visible light cameras are directly arranged on two surfaces parallel to the GEO orbital plane; the fields of view of the four cameras on the four turntables and the two cameras on the upper and lower surfaces of the four cameras substantially cover 360-degree stereoscopic space around the GEO satellite;
the four turntables control the four visible light cameras positioned on the orbital plane to avoid direct sunlight and cover other spatial areas simultaneously according to the position and angle relation between the GEO satellite and the sun;
the solar blind ultraviolet camera is arranged on the GEO satellite, and the view field of the solar blind ultraviolet camera is kept to cover the earth all the time;
and the image processing module judges whether a target needing warning exists according to the optical image acquired by the visible light camera and the ultraviolet image acquired by the ultraviolet camera.
As a preferable aspect of the present invention, the half field angle of each visible light camera is 50 °. According to the half-field angle, the detection distance and the target characteristics of each visible light camera, a large-area array large-size optical detector is selected, so that the optical system is ensured to have a large entrance pupil caliber and has the sensitivity of more than 5 equi-stars. When the turntable is used for controlling the visible light camera to avoid direct sunlight, the maximum sunlight avoiding angle view field is 34 degrees.
As a preferred scheme of the invention, when judging whether the target needing to be alarmed exists, the star points and the image noise points in the optical image are removed according to whether the detected target moves.
As a preferable scheme of the invention, when judging whether the target needing to be alarmed exists, the detection probability and the acting distance of the visible light camera are improved by using a method of increasing the exposure time.
In a preferred embodiment of the present invention, the optical system of the solar blind ultraviolet camera has a field of view of 18 ° x 18 ° and covers the entire earth.
As a preferred scheme of the invention, the angle adjusting function of the turntable is utilized to ensure that the included angle between the pointing direction of the upper edge or the lower edge of the view field and the sun is always kept unchanged (namely the sun avoiding angle), and simultaneously the satellite body is ensured not to shield the other view field edge of the camera, namely the upper edge and the lower edge of the view field of the visible light camera are limited by the sun ray direction and the surface of the satellite body.
As a preferred embodiment of the present invention, since the visible camera is located on the edge line and adjacent to two faces of the satellite, the optical axis is directed to two alternative upper and lower edge ranges. When the included angle between the edge of the camera view field and one of the satellite surfaces is slowly adjusted to be smaller than 1 degree, the direction of the optical axis needs to be adjusted in a large range, the view field is switched to the other upper edge and the lower edge, and the direction of the edge of the view field which is close to the satellite surface is adjusted to be smaller than 1 degree.
As a preferable scheme of the invention, the adjustment direction of the one-dimensional turntable is parallel to the GEO orbit surface.
As a preferred scheme of the invention, the included angle between the edge of the field of view of 2 cameras on the edge and the sun ray is always the sun avoidance angle, and the other 2 cameras capable of adjusting the pointing direction dynamically adjust the pointing angle of the optical axis as well, so that the angle among the cameras is ensured to be fixed, and the whole airspace is uniformly covered.
As a preferable scheme of the invention, when judging whether the target needing to be alarmed exists, whether the target is close to the satellite is judged according to whether the gray level of the detected target is in a significant increasing trend.
As a preferred scheme of the invention, the moving target is confirmed by the trailing phenomenon of the long-time exposure moving target, and the star point target is directly removed by star map identification.
As a preferable scheme of the invention, when seasons change, the included angle is formed between the GEO orbital plane and the ecliptic plane, the maximum avoidance angle which can be realized is increased by 0.5 degrees, the avoidance condition is looser, and the camera pointing adjustment strategy and the angle range are not influenced by seasons. The solar blind ultraviolet camera detector is preferably a large area array detector with longer acting distance. Based on the 32-degree avoidance angle, the coverage rate of the whole alarm space is larger than 90%.
As a preferred scheme of the invention, the light shield can adopt a special-shaped structure to prevent sunlight from directly entering the inner side of the light shield, but a rolling rotary table is matched at the same time, and when the optical axis of the camera is adjusted in a large range, the direction of the light shield with the different-shaped structure is adjusted to rotate 180 degrees for shielding the sun.
A photoelectric detection method for omnidirectional GEO satellite alarm comprises the following steps:
s1, enabling the GEO satellite to be equivalent to a cuboid, and respectively installing four visible light cameras on four edges, perpendicular to the GEO orbital plane, of the GEO satellite; installing two visible light cameras on two surfaces parallel to the GEO orbital plane; the fields of view of the six visible light cameras cover 360-degree stereoscopic space around the GEO satellite to the maximum extent;
s2, controlling four visible light cameras on the edge to avoid direct sunlight according to the position and angle relation between the GEO satellite and the sun;
s3, installing at least one solar blind ultraviolet camera on the GEO satellite, and keeping the view field of the solar blind ultraviolet camera to cover the earth all the time;
and S4, judging whether a target needing to be warned exists according to the optical images acquired by the six visible light cameras and the ultraviolet image acquired by the at least one solar blind ultraviolet camera.
Example (b):
a photoelectric detection system and method for omnidirectional alarm of GEO satellite features that the solid angle of alarm field covers more than 80% of the solid angle of 4 pi, the alarm distance is not less than 50km for the target with 10cm X10 cm size, so avoiding the interference of sun and easily realizing volume and weight.
1. General technical scheme
Aiming at the characteristics that the GEO orbit is high and the satellite is in a solar illumination area most of time, the scheme that the passive detection of visible light is mainly adopted for space debris and the solar blind ultraviolet absorption wave band is assisted is adopted, and 360-degree omnidirectional coverage (except the direction of direct solar radiation) is realized through the spatial composite detection of a plurality of large-view-field visible light imaging detection systems. The optical alarm detection system is arranged on the two-dimensional rotary table, and avoids direct sunlight and dynamically adjusts the pointing direction. Solar blind ultraviolet band detection mainly solves the problem that the earth background is too bright. The reason that field splicing is adopted instead of omni-directional scanning of the rotary table is that the rotary table bearing of the scanning system has a service life problem. The overall scheme is shown in figure 1.
2. Field of view design
The important technical indexes of the threat alarm are the azimuth coverage and the detection distance, and the indexes corresponding to the optical system are the field of view and the sensitivity. For simplicity, the satellite is treated as a hexahedron, with one visible light camera disposed on each side, thus covering the entire 360 ° space with 6 cameras. The angle of view required for a single camera arranged as described above is calculated below. The half field of view is known as θ0The solid angle corresponding to the camera is 2 pi (1-cos theta)0) 6 cameras are required to realize 360-degree space full coverage and have 2 pi (1-cos theta)0) A half field angle θ can be obtained as 4 pi/60Approximately 50 deg., and a full field of view of 100 deg..
3. Optical detection chip selection
The following is a design with a 100 ° field of view, taking into account the detection range. Since the detection distance is related to the target characteristics, the stronger the target, the farther the same detector detects. The sensitivity of the detection system is simply compared, and the detectability of the system is characterized by detectable stars or the like, in order to be independent of the influence of the target characteristics.
For a visible light system, because a target is far, usually in the order of tens of kilometers to hundreds of kilometers, the target radiation to a detector can be approximately parallel light, and the parallel light is converged on one pixel after passing through an optical system, so that factors influencing the sensitivity mainly include the sensitivity of the detector and the light transmission aperture of the optical system. The aperture of the clear light is related to the field of view, generally, the negative correlation relationship is obtained, the larger the field of view is, the smaller the corresponding focal length of the same detector is, and the smaller the aperture can be realized. Therefore, the field of view and the aperture are in a pair of contradictory relations, the solution of the invention is to select a large-scale large-size detector, such as a GSENSE 6060 series CMOS detector with a long photoscope core, the pixel scale is 6144 multiplied by 6144, the pixel size is 10 μm, the detector size is 61.44mm multiplied by 61.44mm, the 100-degree field of view corresponds to a focal length of 21.5mm, the entrance pupil aperture is 18mm, and the detection capability of 5 equi-stars can be achieved through a longer exposure time (10 ms). The optical system designed for the above indices of focal length, entrance pupil, and field of view is shown in fig. 2, and the system is a pure refractive system and a wide-angle field of view.
4. Solar evasion angle design under condition of backlight detection under direct solar radiation
Along with the rotation of the satellite, the direct solar angle changes constantly with time, and if the sun directly enters a view field, the camera is saturated, detection cannot be completed, and the whole camera is invalid.
In order to solve the problems, each optical system is provided with a one-dimensional turntable, so that adjustment in a single direction can be realized, the adjustment direction is parallel to the orbital plane, the optical axis of the optical detection system is pointed to change along with the direction of the sun, the situation that the sun directly irradiates the camera is avoided, the influence of the sun on the work of the camera is reduced to the maximum extent, the range of a solar blind area is limited to be the avoidance angle of the camera, and the solar avoidance angle is designed to be 20-34 degrees outside the visual field. As shown in fig. 1, the solar blind area is a cone angle with a half angle of 20 °, the corresponding solid angle accounts for 3% of the total airspace, the half angle of 34 ° of the cone angle accounts for 8.5% of the total airspace, and the coverage rate of the whole alarm space is greater than 90%.
The larger the evasion angle is, the higher the solar blind area ratio is, and the advantage is that the design realization difficulty of lens hood is less. The sun avoidance angle is realized by using a light blocking ring and a light shield, the minimum value is realized by considering the design realization cost, and the minimum value is 20 degrees in the embodiment.
The avoidance angle is designed to be 34 ° at the maximum for the following reasons. As shown in fig. 3, considering that the included angle between two surfaces of the 6-surface body is 270 °, the space included angle is divided into an upper area and a lower area of sunlight by the incident sunlight, wherein the upper boundary of the first area is the surface 4, and the lower boundary is the upper boundary of the sun avoidance cone angle. The upper boundary sun of the second area avoids the lower boundary of the cone angle, and the lower boundary is a surface 3. The optical axis is typically placed over a large angular range. When the incident direction of the sun bisects an included angle of 270 degrees, the ranges of the first area and the second area are the same, the moment of the field of view which is the most difficult to avoid is the moment, the field of view of the camera can only be within 135 degrees of the incident direction of the sun and the plane 4 or the plane 3, the field of view of the camera is considered to be 100 degrees, at least 1 degree of space needs to be reserved between the field of view of the camera and the plane of the satellite, the field of view of the camera is prevented from being carried out by the satellite, the camera is.
5. Optical axis pointing adjustment scheme for camera on four rotary tables
When the satellite moves along with the orbit, the solar incident angle is unchanged, but the direction of the optical axis of the camera changes along with the orbit, the included angle between the edge direction of the view field and the sun is kept unchanged by utilizing the angle adjusting function of the turntable, and meanwhile, the satellite body is ensured not to shield the view field of the camera. When the camera 4 is moved to the 45 ° position in fig. 1, the upper edge of the camera 4 makes an angle of 34 ° with the direction of the sun's rays, and the lower edge makes an angle of 1 ° with the face 3, as shown in fig. 3. When the optical axis direction of the camera is adjusted along with the track angle, the surface 3 blocks the view field of the camera 4, so that the optical axis direction is adjusted in a large range at the time, and the included angle between the lower edge of the adjusted camera view field and the sunlight direction is 34 degrees, as shown in fig. 4.
As shown in fig. 1, when the satellite is located at the leftmost side of the orbit, the included angle between the lower edge direction of the field of view of the camera 1 and the incident direction of the sun is adjusted to be 20-34 degrees of the evading angle of the sun, the full field of view of the camera 1 is 100 degrees, and then the included angle between the right edge of the field of view of the camera and the face 1 of the satellite is 60-56 degrees. The included angle between the direction of the optical axis of the camera 2 and the direction of the optical axis of the camera 1 is designed to be 73.4-76 degrees, the included angle between the camera 2 and the camera 3 is consistent with that between the camera 2 and the camera 1, the total of the fields of view of the four cameras is 400 degrees, the full avoidance angle range of 40-68 degrees is removed, and the overlapped field of view area is 80-108 degrees. The included angle between the upper edge of the view field of the camera 4 and the incident direction of the sun is consistent with that of the camera 1, and is a sun avoidance angle.
The incident angle between the cameras on the two surfaces of the parallel orbit surface in the hexahedral satellite and the sun is larger, so that the problem of direct interference of the sun does not exist, and the angle is always kept unchanged.
6. Detection of the Earth's background
Looking at the earth from GEO orbit, the earth occupies approximately a 17 ° × 17 ° field of view within which visible light for viewing 5 equistars is saturated. Furthermore, since the threat object is a point object image and the earth is a surface object image, the energy of the threat object is much less than the energy of the earth background, and object detection is difficult. Therefore, a solar blind ultraviolet camera is used for detection. Solar blind ultraviolet radiation with the wavelength of 200-300nm is absorbed by ozone of an atmospheric stratosphere, almost no scattering occurs, and background radiation is smooth.
7. Image processing
The core tasks of image processing are to reduce the false alarm probability (no target, but target judged by algorithm) and to increase the detection probability (target, algorithm can detect).
The detection probability is mainly related to the signal-to-noise ratio of the target, reliable detection can be realized, and the signal-to-noise ratio is generally required to reach 8-10. The core of reducing the false alarm rate of the visible light detection system is that the algorithm can distinguish the detector noise point, the star point and the real target. Due to the sensitivity of 5 equi-stars and the number of star points in a 100-degree field of view is nearly hundreds, the target detection is interfered. The essential difference between the real target and the star point and the noise point is that the target moves, and the target can be detected according to whether the target moves or not in the image processing. And simultaneously, star maps are used for identifying and matching the star points in the visual field one by one, and the unsuccessfully matched star points are suspicious targets. In addition, in order to determine whether the target approaches the satellite, the gray scale of the target needs to be monitored to determine whether the target gray scale is in a situation of continuously increasing.
Because the stability of the satellite platform in the GEO orbit is good, the residual angular velocity is less than 0.01 degrees/s, the angle covered by a single pixel is 100 degrees/6144 degrees to 0.016 degrees, which corresponds to 0.283 mrad. Assuming that the target is 200km away from the satellite and the flying speed is 4km/s, the maximum angular speed of the target motion is 20 mrad/s. The maximum exposure time for the target without motion tailing on the image can be up to 5 ms. In actual detection, the exposure time can be further increased for a deep space background, the exposure time of more than 10ms is adopted, on one hand, the accumulation of target signals is increased, on the other hand, if the target has a vertical movement speed relative to a target-satellite connecting line, the trailing phenomenon can be detected, and the trailing phenomenon is used as a basis for distinguishing a static target, so that the detection of the moving target is facilitated, and the detection probability is improved.
8. Detection distance evaluation
Assuming that the object is a sphere with a radius of 0.282m, the reflection section thereof is always kept constant at 0.25m2The hemispherical reflectivity to the sun is 0.85 and is a lambert diffuser. Obviously, the equivalent brightness of the target is related to the sun phase angle θ, and the meaning of the sun phase angle is shown in fig. 5, which represents the included angle between the optical axis direction vector and the target-to-sun direction vector.
Assuming that the target is beyond 400km, a target star and the like and sun phase angle relation graph is calculated, as shown in FIG. 6.
The above is the calculation result of the spherical object, and the actual situation is more complicated than this, and has a relation with the structure, surface material, posture and the like of the object.
Another set of calculations is performed below, assuming that the target is a cube, 0.5m in length, and the irradiance of the target at a certain distance can be calculated by:
Figure BDA0002731555740000121
in the above formula, ρ is the target reflectivity, EsunIs solar irradiance, R is irradiation distance, cos theta1cosθ2Is a cornerThe coefficient, S, is the target radiation area. The spectral range of the calculated target illumination is 400-900 nm. The angular coefficient and the target reflectivity taken together are taken to be 0.3, i.e. ρ cos θ1cosθ2The average value was 0.3. 0.25m is given below2The visual star values of the target at different distances are shown in table 1.
TABLE 1
Target distance (km) 25 50 75 100 150 200
Apparent star equal value (Mv) 0.1 1.6 2.5 3.2 4.1 4.7
In summary, if the sensitivity of the visible light detection system can be up to 5 stars, for 0.25m2The detection distance is more than 200 km. For 0.0625m2Target, target characteristic is 4 times weaker, detection distanceHalved to 100 km.
8. Analysis of influence of seasonal changes on avoidance angle
As shown in fig. 7, when the GEO orbit is located at the ecliptic plane, the solar incidence direction is perpendicular to the edge line on which the camera is placed, at this time, the incidence direction is on, the camera optical axis direction is oc, the camera view field lower edge 1 is op, angle cop is 50 ° in half view field size, and angle pos is the solar avoidance angle, which is taken as 34 °. When the season changes, for example, in winter, the angle between the incident direction 2om of the sun and the incident direction 1on is 23.4 °, cos (═ com) × cos (× com) is present according to the geometric relationship, and the carried-in data angle com is 84.5 °.
The angle between the lower edge 2 of the camera and the optical axis is calculated below. Assuming that the co length is 1, the cp length is tan50, the cn length is tan84, the mn length is tan23.4 × 1/cos (84), and the qp length is tan23.4 × 1/cos (84) × tan50/tan 84; the op length is 1/cos50, and the angle qop is 18.43 degrees. According to the geometric relationship, cos coq ═ cos ═ cop × cos ═ qop, the ═ coq ═ 52.42 ° can be obtained. At the moment, the angle between the incident direction of the sun and the edge of the camera field of view is equal to qom-84.5-52.4-32 degrees, and the change of the angle is not large as the maximum avoidance angle of 34 degrees at the beginning of spring, so that unidirectional adjustment by using a one-dimensional turntable is completely feasible and is not influenced by seasons, and the maximum avoidance angle is 32 degrees.
Those skilled in the art will appreciate that those matters not described in detail in the present specification are well known in the art.
Although the present invention has been described with reference to the preferred embodiments, it is not intended to limit the present invention, and those skilled in the art can make variations and modifications of the present invention without departing from the spirit and scope of the present invention by using the methods and technical contents disclosed above.

Claims (13)

1. A photoelectric detection system for omnidirectional GEO satellite alarm is characterized by comprising an image processing module, four turntables, six visible light cameras and a solar blind ultraviolet camera;
the GEO satellite is equivalent to a cuboid, four turntables are respectively arranged on four edges perpendicular to a GEO orbital plane on the GEO satellite, each turntable is provided with a visible light camera, and the other two visible light cameras are directly arranged on two surfaces parallel to the GEO orbital plane; the fields of view of the six visible light cameras cover 360-degree stereoscopic space around the GEO satellite to the maximum extent;
the four turntables control the four visible light cameras to avoid direct sunlight according to the position and angle relation between the GEO satellite and the sun;
the solar blind ultraviolet camera is arranged on the GEO satellite, and the view field of the solar blind ultraviolet camera is kept to cover the earth all the time;
the image processing module judges whether a target needing warning exists according to an optical image acquired by the visible light camera and an ultraviolet image acquired by the solar blind ultraviolet camera.
2. The photodetection system for GEO satellite omnidirectional alerts according to claim 1, characterized in that the half field angle of each visible light camera is 50 °.
3. The photoelectric detection system for the omnidirectional GEO satellite alarm is characterized in that an optical detector is selected according to the half-field angle, the detection distance and the target characteristic of each visible light camera, and the sensitivity of the optical detector reaches 5 stars and above.
4. The photoelectric detection system for the omnidirectional GEO satellite alarm of claim 1, wherein when judging whether the target needing alarm exists, the star points and the image noise points in the optical image are removed according to whether the detected target moves.
5. The photoelectric detection system for the omnidirectional GEO satellite alarm of claim 1, wherein when determining whether there is an object needing alarm, the detection probability and the working distance of the visible light camera are increased by increasing the exposure time.
6. The photoelectric detection system for the omnidirectional GEO satellite alarm is characterized in that the maximum sun avoiding angle field of view is 34 degrees when the turntable is used for controlling the visible light camera to avoid the direct sunlight.
7. The photoelectric detection system for omnidirectional GEO satellite alarm according to any one of claims 1-5, characterized in that the field of view of the solar blind ultraviolet camera optical system is 18 ° x 18 °.
8. The photoelectric detection system for the omnidirectional GEO satellite alarm of claim 6, wherein the turntable angle adjustment function is utilized to keep the angle between the pointing direction of the upper edge of the visual field of the visible light camera and the sun or the angle between the pointing direction of the lower edge of the visual field of the visible light camera and the sun constant, and simultaneously the satellite body does not shield the other visual field edge of the camera, i.e. the upper and lower edges of the visual field of the visible light camera are limited by the direction of the sun rays and the surface of the satellite body.
9. The photo detection system for omnidirectional GEO satellite alarm according to claim 8, wherein for any one of the visible light cameras on the edge, as the position and angle of the satellite and the sun changes, when the angle between one of the camera view field edges pointed by the optical axis of the visible light camera and the adjacent satellite surface is less than 1 °, the optical axis pointing direction of the visible light camera is adjusted so that the angle between the camera view field edge and the sun incident direction is the sun avoidance angle.
10. The photoelectric detection system for the omnidirectional GEO satellite alarm of any one of claims 1 to 5, wherein the turntable is a one-dimensional turntable, and the adjustment direction of the turntable is parallel to the GEO orbit plane.
11. The photo-electric detection system for omnidirectional GEO satellite alarm of claim 1, wherein when determining whether there is an object needing alarm, when the gray scale of the detected object is 4 times or more of the gray scale of the detected object at the moment of being found, the approaching satellite of the detected object is determined.
12. The photoelectric detection system for the omnidirectional GEO satellite alarm is characterized in that the moving target is confirmed by utilizing the trailing phenomenon of the long-time exposure moving target, and the star point target is directly removed through star map identification.
13. A photoelectric detection method for omnidirectional GEO satellite alarm is characterized by comprising the following steps:
s1, enabling the GEO satellite to be equivalent to a cuboid, and respectively installing four visible light cameras on four edges, perpendicular to the GEO orbital plane, of the GEO satellite; installing two visible light cameras on two surfaces parallel to the GEO orbital plane; the fields of view of the six visible light cameras cover 360-degree stereoscopic space around the GEO satellite to the maximum extent;
s2, controlling four visible light cameras on the edge to avoid direct sunlight according to the position and angle relation between the GEO satellite and the sun;
s3, installing at least one solar blind ultraviolet camera on the GEO satellite, and keeping the view field of the solar blind ultraviolet camera to cover the earth all the time;
and S4, judging whether a target needing to be warned exists according to the optical images acquired by the six visible light cameras and the ultraviolet image acquired by the at least one solar blind ultraviolet camera.
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