CN112505795B - Photoelectric detection system and method for GEO satellite omnidirectional alarm - Google Patents
Photoelectric detection system and method for GEO satellite omnidirectional alarm Download PDFInfo
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Abstract
A photoelectric detection system and method for omni-directional alarming of GEO satellite, belong to the technical field of omni-directional alarming, equivalent GEO satellite to a cuboid, install four turntables on four edges perpendicular to GEO orbit surface on GEO satellite separately, install a visible light camera on each turntable, two other cameras are installed on two surfaces parallel to GEO orbit surface directly; the four turntables control four visible light cameras in the GEO track surface 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 cover a space region except for a sun avoidance angle; at least one solar blind ultraviolet camera is installed on the GEO satellite, and the field of view of the ultraviolet camera is kept to always cover the earth; and judging whether a target needing warning exists or not according to the optical images acquired by the six visible light cameras and the ultraviolet images acquired by the at least one ultraviolet camera.
Description
Technical Field
The invention relates to a photoelectric detection system and a photoelectric detection method for omni-directional alarming of a GEO satellite, and belongs to the technical field of omni-directional alarming.
Background
GEO satellites are typically high value satellites that are of great significance for safe operation. GEO satellites are currently facing mainly space debris threats.
With the increasing space activities of human exploration in space, space debris environments are increasingly severe. Although most of the space debris is small in size, most of the debris is in the order of centimeters in millimeter, it is surprisingly destructive. The huge 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 several kilometers per second, the collision kinetic energy is huge, once the space debris collides with a satellite, the space debris can cause perforation damage to satellite parts, and the satellite can completely fail and even be in catastrophic disassembly due to heavy weight.
Because the fragments are small in size and too many in quantity, the orbits of the fragments cannot be measured one by one, the spacecraft cannot implement maneuvering strategies to avoid collision, and the spacecraft can only be protected to improve the immunity of the spacecraft. In order to achieve avoidance of space debris collisions by a spacecraft, space debris collision threat warning must be completed.
The current satellite omnidirectional alarm technology has the following problems to be solved:
1) Large alarm field of view
2) Long detection distance
3) Target size is small
4) The presence of solar radiation and earth background interference
5) Multiple technical problems such as limited volume, weight and power consumption
Disclosure of Invention
The invention aims to solve the technical problems that: the photoelectric detection system and the method for the GEO satellite omnidirectional alarm are provided, the GEO satellite is equivalent to a cuboid, four turntables are respectively arranged on four edges of the GEO satellite, which are perpendicular to the GEO track surface, each turntable is provided with a visible light camera, and the other two cameras are directly arranged on two surfaces parallel to the GEO track surface; the fields of view of six visible light cameras in total of four cameras on the four turntables and two cameras on the upper and lower surfaces basically cover 360-degree stereoscopic space around the GEO satellite; the four turntables control four visible light cameras in the GEO track surface 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 cover a space region except for a sun avoidance angle; at least one solar blind ultraviolet camera is installed on the GEO satellite, and the field of view of the ultraviolet camera is kept to always cover the earth; and judging whether a target needing warning exists or not according to the optical images acquired by the six visible light cameras and the ultraviolet images acquired by the at least one ultraviolet camera.
The invention aims at realizing the following technical scheme:
a photoelectric detection system for a GEO satellite omnidirectional 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 of the GEO satellite, which are perpendicular to the GEO track surface, 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 track surface; the visual fields of the six visible light cameras maximally cover 360-degree stereoscopic space around the GEO satellite;
the four turntables control the four visible light cameras to avoid direct solar radiation 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 always cover the earth;
and the image processing module judges whether a target needing warning exists or not according to the optical image acquired by the visible light camera and the ultraviolet image acquired by the solar blind ultraviolet camera.
The photoelectric detection system for the GEO satellite omni-directional 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, preferably, 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 sampsonies and more.
In the above photoelectric detection system for omni-directional alarm of GEO satellite, preferably, when judging whether there is a target to be alarmed, the star point and the image noise point in the optical image are removed according to whether there is motion of the detected target.
In the above photoelectric detection system for omni-directional alarm of GEO satellite, preferably, when judging whether a target requiring alarm exists, the detection probability and the action distance of the visible light camera are improved by using a method of increasing exposure time.
In the above photoelectric detection system for omni-directional alarming of GEO satellites, preferably, when the visible light camera is controlled to avoid direct sunlight by using the turntable, the maximum solar avoidance angle field of view is 34 °.
Preferably, the field of view of the solar blind ultraviolet camera optical system of the photoelectric detection system for the omnidirectional alarm of the GEO satellite is 18 degrees multiplied by 18 degrees.
According to the photoelectric detection system for the GEO satellite omnidirectional alarm, preferably, by utilizing the turntable angle adjusting function, the angle between the upper edge direction of the visual field of the visible light camera and the sun or the angle between the lower edge direction 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 visual field edge of the camera, namely, the upper edge and the lower edge of the visual field of the visible light camera are limited by the direction of solar rays and the surface of the satellite body.
In the above photoelectric detection system for omni-directional alarm of a GEO satellite, preferably, for any one of the visible light cameras located on the edge, when an included angle between one of the edges of the field of view of the visible light camera pointed by the optical axis and an adjacent one of the satellite surfaces is smaller than 1 ° along with the position and angle change of the satellite and the sun, the optical axis pointing of the visible light camera is adjusted so that the included angle between the edge of the field of view of the camera and the incident direction of the sun is a sun avoidance angle.
In the above photoelectric detection system for omni-directional alarm of GEO satellites, preferably, the turntable is a one-dimensional turntable, and the adjustment direction of the turntable is parallel to the GEO orbit plane.
In the above photoelectric detection system for GEO satellite omni-directional warning, it is preferable that when judging whether or not there is an object to be warned, if the gray scale of the detected object is 4 times or more the gray scale of the detected time, the approaching satellite of the detected object is judged.
In the above photoelectric detection system for omni-directional alarming of GEO satellites, preferably, the moving object is confirmed by using a tailing phenomenon of the moving object exposed for a long time, and the star point object is directly removed by star map recognition.
A photoelectric detection method for the omnidirectional alarm of a GEO satellite comprises the following steps:
s1, equivalent a GEO satellite to be a cuboid, and respectively installing four visible light cameras on four edges of the GEO satellite, which are perpendicular to a GEO track surface; mounting two visible light cameras on two surfaces parallel to the GEO-track surface; the visual fields of the six visible light cameras maximally cover 360-degree stereoscopic space around the GEO satellite;
s2, controlling four visible light cameras on the edge to avoid direct solar radiation 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 field of view of the solar blind ultraviolet camera to always cover the earth;
s4, judging whether a target needing warning exists or not according to the optical images acquired by the six visible light cameras and the ultraviolet images acquired by the at least one solar blind ultraviolet camera.
Compared with the prior art, the invention has the following beneficial effects:
(1) The method fully utilizes the characteristic that GEO orbit space fragments are irradiated by the sun, adopts a plurality of large-view-field visible light cameras to passively detect, and reduces the volume, the weight and the power consumption of the system to the greatest extent compared with active detection such as microwaves or laser radars.
(2) Aiming at the problem that the normal operation of a visible light camera is affected due to continuous change of the incident angle of the sun caused by satellite orbital motion, the camera is provided with an angle adjustment turntable, an optimal pointing area is automatically calculated, sunlight can be prevented from directly entering a view field to interfere normal imaging, and meanwhile, the satellite body is prevented from shielding the camera for imaging, so that the whole space coverage rate is more than 90%.
(3) In order to avoid the influence of sunlight reflected by the earth on a visible light camera, a solar blind ultraviolet camera is provided, always points to the earth area, fills the gap of the alarm of the partial view field, obviously absorbs the atmospheric air of the solar blind ultraviolet earth, furthest reduces the background of an image, and greatly improves the volume, the weight and the acting distance of the scheme relative to an infrared detection scheme of an atmospheric absorption wave band;
(4) When the ultra-large area array visible light detector is adopted, the large entrance pupil size is realized during large-view-field detection, the sensitivity of the system is easy to ensure, and a large acting distance can be realized;
(5) Compared with the omnidirectional scanning, the bearing service life problem faced by the turntable high-speed scanning can be avoided by adopting a large-view-field gaze detection imaging scheme.
(6) Different from the traditional method for avoiding motion tailing in the setting of the exposure time of the detection system, the method is convenient for distinguishing a moving target and a static target by adopting long exposure time aiming at a deep space background, accumulating target signals on one hand, increasing the acting distance of the detection system and detecting the motion tailing phenomenon of the target on the other hand.
(7) Compared with the scanning scheme, the technical scheme of the invention has the advantages that the image detection is easier to detect the moving target due to the good stability of the platform, and the requirement of self motion decoupling is avoided.
(8) The installation position of the visible light camera selects the most edge position of the satellite, such as an edge, so that the restriction of the satellite body on the observation view field is reduced to the maximum extent, and all space areas except for the solar evasion angle can be covered.
(9) The technology of the invention confirms that the visible light field size is 100 degrees multiplied by 100 degrees, the maximum solar avoidance angle which can be realized for the hexahedral satellite is 32 degrees, and the coverage rate of the whole warning 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 avoidance angle, and the scheme has good adaptability.
(11) The directional adjustment scheme is not affected by seasons, the one-dimensional turntable is adjusted in one direction, and complexity caused by using two dimensions is avoided.
Drawings
FIG. 1 is a schematic diagram showing the continuous adjustment and variation of a visible light camera along with the operation of a satellite;
FIG. 2 is a schematic diagram of a 100 wide angle field optical system;
FIG. 3 is a schematic illustration of a 34℃calculation of the maximum value of the avoidance angle;
fig. 4 is a schematic diagram of a wide range adjustment of camera pointing. When the incident direction of the sun passes through the bisector of the plane 3 and the plane 4, in order to avoid the shielding of the view field by the plane 3, the optical axis direction of the camera needs to be adjusted up and down, and the downward direction of the figure 2 is adjusted to be the upward direction of the figure;
FIG. 5 is a schematic diagram showing the meaning of solar phase angle θ, showing the angles between the optical axis direction vector and the target-to-solar direction vector;
FIG. 6 is 0.25m beyond 400km 2 A target star of a reflection section and a solar phase angle relation diagram;
fig. 7 shows the influence of seasonal variation on the avoidance angle.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.
A photoelectric detection system for the omnidirectional alarm of a GEO satellite 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 of the GEO satellite, which are perpendicular to the GEO track surface, 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 track surface; the fields of view of six visible light cameras in total of four cameras on the four turntables and two cameras on the upper and lower surfaces basically cover 360-degree stereoscopic space around the GEO satellite;
the four turntables control four visible light cameras positioned on the track surface to avoid direct sunlight according to the position and angle relation between the GEO satellite and the sun, and cover other space areas;
the solar blind ultraviolet camera is arranged on the GEO satellite, and the view field of the solar blind ultraviolet camera is kept to always cover the earth;
the image processing module judges whether a target needing warning exists or not according to the optical image acquired by the visible light camera and the ultraviolet image acquired by the ultraviolet camera.
As a preferred embodiment of the present invention, the half field angle of each visible light camera is 50 °. According to the half field angle, detection distance and 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 the sensitivity of more than 5 sampsons is achieved. When the turntable is used for controlling the visible light camera to avoid direct sunlight, the maximum solar avoidance angle view field is 34 degrees.
As a preferable scheme of the invention, when judging whether an object needing to be alarmed exists, star points and image noise points in the optical image are removed according to whether the detected object moves.
As a preferable scheme of the invention, when judging whether a target needing warning exists, the detection probability and the acting distance of the visible light camera are improved by using a method for increasing the exposure time.
As a preferable mode of the invention, the field of view of the solar blind ultraviolet camera optical system is 18 degrees×18 degrees, and the whole earth direction is covered.
As a preferable scheme of the invention, the angle adjusting function of the turntable is utilized to ensure that the included angle between the upper edge or the lower edge of the view field and the sun is always kept unchanged (namely, the sun evasion angle), and meanwhile, the satellite body is ensured not to shade 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 direction of solar rays and the surface of the satellite body.
As a preferred embodiment of the invention, the optical axis is directed to have two alternative upper and lower edge ranges, since the visible camera is located on the line of the prism, adjacent to both sides of the satellite. When the angle between the edge of the view field of the camera and one of the satellite surfaces is slowly adjusted to be smaller than 1 degree, the optical axis direction needs to be adjusted in a large range, the view field is switched to the other upper and lower edges, 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 with the other upper and lower edges and the other surface of the satellite.
As a preferable mode of the present invention, the one-dimensional turntable is adjusted in a direction parallel to the GEO track surface.
As a preferable scheme of the invention, the included angle between the edges of the view field of 2 cameras and the sun rays is always the sun evasion angle, and the other 2 cameras with adjustable directives also dynamically adjust the optical axis directionality angle, so that the fixed angle among the cameras is ensured, and the whole airspace is uniformly covered.
As a preferable scheme of the invention, when judging whether the object needing to be alarmed exists, judging whether the object is close to the satellite according to whether the gray level of the detected object is in a significant increasing trend.
As a preferable scheme of the invention, the moving object is confirmed by the tailing phenomenon of the moving object after long-time exposure, and star point objects are directly removed by star map recognition.
As a preferable scheme of the invention, when the season changes, the GEO track surface and the yellow track surface have an included angle, the maximum avoidance angle which can be realized can be increased by 0.5 DEG, the avoidance condition is more relaxed, 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, and has a longer action distance. Based on the 32-degree evasion angle, the coverage rate of the whole alarm space is more than 90 percent.
As a preferable scheme of the invention, the shading cover can adopt a special-shaped structure, so that sunlight is prevented from directly entering the inner side of the shading cover, but a rolling turntable is needed to be matched, and when the optical axis of the camera is adjusted in a large range, the direction of the shading cover with the special-shaped structure is adjusted to rotate 180 degrees so as to shade the sun.
A photoelectric detection method for the omnidirectional alarm of a GEO satellite comprises the following steps:
s1, equivalent a GEO satellite to be a cuboid, and respectively installing four visible light cameras on four edges of the GEO satellite, which are perpendicular to a GEO track surface; mounting two visible light cameras on two surfaces parallel to the GEO-track surface; the visual fields of the six visible light cameras maximally cover 360-degree stereoscopic space around the GEO satellite;
s2, controlling four visible light cameras on the edge to avoid direct solar radiation 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 field of view of the solar blind ultraviolet camera to always cover the earth;
s4, judging whether a target needing warning exists or not according to the optical images acquired by the six visible light cameras and the ultraviolet images acquired by the at least one solar blind ultraviolet camera.
Examples:
a photoelectric detection system and a photoelectric detection method for the omnidirectional alarm of a GEO satellite, wherein the solid angle of an alarm view field covers more than 80% of the 4 pi solid angle, the alarm distance is not less than 50km for a 10cm multiplied by 10cm size target, the solar interference can be avoided, and the volume and the weight are easy to realize engineering.
1. General technical scheme
Aiming at the characteristics that GEO orbits are high and satellites are in a solar illumination area for most of the time, the scheme that visible light passive detection is adopted mainly and solar blind ultraviolet absorption wave bands are adopted as assistance is adopted for space debris, and 360-degree omnidirectional coverage (except for the direct solar radiation direction) is realized through 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 turntable, so that direct solar radiation is avoided, and the direction is dynamically adjusted. The solar blind ultraviolet band detection mainly solves the problem of too bright earth background. The view field stitching is adopted instead of the turntable omnidirectional scanning, because the turntable bearing of the scanning system has a service life problem. The general scheme is shown in fig. 1.
2. Field of view design
Important technical indexes of threat warning are azimuth coverage and detection distance, and indexes corresponding to an optical system are field of view and sensitivity. For simplicity, the satellite is considered as a hexahedron, with one visible light camera arranged on each side, so that the entire 360 ° space is covered with 6 cameras. The angle of view required for a single camera, arranged as described above, is calculated below. Known half field of view θ 0 The camera corresponding to the (2 pi) (1-cos theta) 0 ) The 6 cameras are required to realize 360-degree space full coverage and have 2 pi (1-cos theta) 0 ) =4pi/6, the half field angle θ can be obtained 0 About 50 deg., with a full field of view of 100 deg..
3. Optical probe chip selection
The following is designed with a 100 field of view, taking into account the detection distance. Since the detection distance is related to the characteristics of the target, the stronger the target, the farther the same detector detects the distance. To simply compare the sensitivity of the detection system independent of the effect of the target characteristics, the detection capability of the system is characterized by a detectable star or the like.
For a visible light system, since the target is far, usually in the order of tens of kilometers to hundreds of kilometers, the target is radiated to the detector and can be approximately parallel light, and the light is converged to one pixel after passing through the optical system, so that factors affecting the sensitivity are mainly the sensitivity of the detector and the light aperture of the optical system. The aperture of the light transmission is related to the field of view, generally in a negative correlation, and the larger the field of view is, the smaller the focal length corresponding to the same detector is, and the smaller the aperture can be realized. Therefore, the view field and caliber are a pair of contradictory relations, and the solution of the invention is to select a large-scale large-size detector, such as GSENSE 6060 series CMOS detector with long light core, the pixel scale is 6144×6144, the pixel size is 10 μm, the detector size is 61.44mm×61.44mm, the 100-degree view field corresponds to a focal length of 21.5mm, the entrance pupil caliber is 18mm, and the detection capability of 5 sampsoles can be realized through longer exposure time (10 ms). The optical system designed for the indexes of the focal length, the entrance pupil and the field of view is shown in fig. 2, and the system is a pure refraction system and a wide-angle field of view.
4. Design of solar evasion angle under backlight detection condition under direct solar irradiation
With the rotation of the satellite, the direct sun angle changes continuously along with time, and if the sun directly enters the field of view, the camera is saturated and cannot finish detection, so that the whole camera is disabled.
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 track surface, the optical axis direction of the optical detection system changes along with the direction of the sun, the condition of direct sunlight of the sun is avoided, the influence of the sun on the work of the camera is reduced to the greatest extent, the range of a solar blind area is limited to an avoidance angle of the camera, and the solar avoidance angle is designed to be 20-34 degrees outside a field of view. As shown in FIG. 1, the solar blind area is a cone angle with a half angle of 20 degrees, the corresponding solid angle is 3% of the full space domain proportion, and the cone angle with a half angle of 34 degrees is 8.5% of the full space domain proportion, so that the coverage rate of the whole alarm space is more than 90%.
The larger the evading angle is, the higher the proportion of the solar blind area is, and the smaller the difficulty of design realization of the shade is. The solar evasion angle is realized by using a light blocking ring and a light shielding cover, the design realization cost is considered in the realization of the minimum value, and the minimum value is 20 degrees in the embodiment.
The avoidance angle is designed to be 34 ° at maximum for the following reasons. As shown in fig. 3, considering that the included angle between two sides of the 6-plane body is 270 °, the incident solar light divides the space included angle into two areas, namely an upper area and a lower area of sunlight, wherein the upper boundary of the first area is the plane 4, and the lower boundary of the first area is the upper boundary of the solar avoidance cone angle. The upper boundary of the second region is the lower boundary of the solar avoidance cone angle, and the lower boundary is the surface 3. The optical axis is typically placed in a larger angular range. When the incident direction of the sun is equal to 270 degrees, the first area and the second area are the same, and the camera view field can only be in 135 degrees between the incident direction of the sun and the surface 4 or the surface 3 for the most difficult view moment, and considering that the view field size of the camera is 100 degrees, at least 1 degree space is required to be reserved between the camera view field and the satellite surface, so that the satellite is prevented from carrying out the camera view field and shielding the camera, and the maximum solar view angle is 34 degrees.
5. Optical axis pointing adjustment scheme for cameras on four rotary tables
When the satellite moves along with the orbit, the incident angle of the sun is unchanged, but the direction of the optical axis of the camera is changed along with the orbit, the 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 shade the view field of the camera. When moving to the 45 ° position of fig. 1, the upper edge of the camera 4 makes an angle of 34 ° with the direction of solar 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 condition that the surface 3 shields the view field of the camera 4 occurs, so that the direction of the optical axis is adjusted in a large range, and the included angle between the lower edge of the view field of the camera and the direction of solar rays is 34 degrees after adjustment, as shown in fig. 4.
As shown in fig. 1, when the satellite is positioned 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 ° of the solar evasion angle, the full field of view of the camera 1 is 100 °, and then the included angle between the right edge of the field of view of the camera and the plane 1 of the satellite is 60 ° -56 °. The included angle between the optical axis direction of the camera 2 and the optical axis direction of the camera 1 is designed to be 73.4-76 degrees, the included angle between the camera 2 and the camera 3, the included angle between the camera 3 and the camera 4 is consistent with the camera 2 and the camera 1, the total view fields of the four cameras are 400 degrees, the full-avoidance angle range of 40-68 degrees is removed, and the overlapped view field area is 80-108 degrees. The included angle between the upper edge of the field of view of the camera 4 and the incident direction of the sun is consistent with that of the camera 1, and the included angle is the sun avoidance angle.
The angle of the cameras on the two parallel track surfaces in the hexahedral satellite is always unchanged because the angle of incidence of the cameras on the two parallel track surfaces with the sun is larger, and the problem of direct solar interference is solved.
6. Detection of earth background
Looking at the earth from the GEO orbit, the earth approximately occupies a 17 x 17 field of view within which a visible camera for looking at a 5-star would saturate. Furthermore, since the threat object is point object imaging and the earth is surface object imaging, the threat object is much less energetic than the earth's background and object detection is difficult. Thus, a solar blind ultraviolet camera is used for detection. Solar blind ultraviolet radiation with the wavelength of 200-300nm is absorbed by ozone in the atmospheric stratosphere, almost without scattering, and the background radiation is smooth.
7. Image processing
The core tasks of image processing are to reduce the false alarm probability (no target, but the algorithm judges that there is a target) and to increase the detection probability (there is a target, the algorithm can detect).
The detection probability is mainly related to the signal-to-noise ratio of the target, and can be reliably detected, and the signal-to-noise ratio is generally required to reach 8-10. The core of the false alarm rate reduction of the visible light detection system is that an algorithm can distinguish between the noise point, the star point and the real target of the detector. Because the sensitivity reaches 5 equal stars, the number of star points in the 100-degree view field is nearly hundred, and interference is formed on target detection. The essential difference between a real target and star points and between the real target and noise points is that the target moves, and the target can be detected according to whether the target moves or not in image processing. And simultaneously, star points in the field of view are subjected to star map identification matching one by utilizing a star table, and the unsuccessfully matched object is suspicious. In addition, in order to determine whether the target approaches the satellite, it is necessary to monitor the gray level of the target to determine whether the gray level of the target is in a continuously increasing situation.
Because the stability of the satellite platform of GEO orbit is very good, the residual angular velocity is less than 0.01 °/s, the angle of single pixel coverage is 100 °/6144=0.016°, corresponding to 0.283mrad. Assuming that the target is 200km from the satellite and the flight speed is 4km/s, the maximum angular velocity of the target motion is 20mrad/s. The maximum exposure time for the object to have no motion smear on the image may be up to 5ms. In the actual detection, the exposure time can be further increased for deep space background, and the exposure time of more than 10ms is adopted, so that on one hand, the accumulation of target signals is increased, and on the other hand, if the target has a motion speed in the vertical direction relative to the target-satellite connection line, the tailing phenomenon can be detected, and the tailing phenomenon is used as a basis for distinguishing stationary targets, thereby facilitating the detection of moving targets and improving the detection probability.
8. Detection distance assessment
Assuming that the target is a sphere with a radius of 0.282m, the reflection section always remains unchanged at 0.25m 2 The hemispherical reflectivity to the sun was 0.85 and was a lambert diffuser. It is apparent that the equivalent brightness of the target is related to the solar phase angle θ, which is defined in fig. 5, which shows the angle between the optical axis direction vector and the target-to-solar direction vector.
The target star and solar phase angle relationship is calculated below assuming the target is outside 400km, as shown in fig. 6.
The above-mentioned calculation result of the spherical target is more complex than this, and has relation with the structure, surface material, posture and the like of the target.
Another set of calculations is performed below, assuming the target is a cube, 0.5m in length, and irradiance of the target at a distance can be calculated by:
ρ is the target reflectivity, E sun Is solar irradiance, R is irradiation distance, cos theta 1 cosθ 2 For the angular coefficient, S is the target radiating area. Calculating spectral range of target illuminance400-900 nm. The angular coefficient and the target reflectivity are taken together to account for 0.3, ρcos θ 1 cosθ 2 The average value was 0.3. The 0.25m is given below 2 The visual star values of the targets at different distances are shown in table 1.
TABLE 1
| Target distance (km) | 25 | 50 | 75 | 100 | 150 | 200 |
| Star equal value (Mv) | 0.1 | 1.6 | 2.5 | 3.2 | 4.1 | 4.7 |
To sum up, if the sensitivity of the visible light detection system can reach 5 equivalents, for 0.25m 2 Is detected at a distance greater than 200km. For 0.0625m 2 The target characteristic is weaker by 4 times, the detection distance is halved, and the detection distance is 100km.
8. Analysis of influence of seasonal variation on avoidance angle
As shown in fig. 7, when the GEO track is located on the side of the yellow road, the incident direction of the sun is perpendicular to the ridge line on which the camera is placed, the incident direction is on, the optical axis direction of the camera is oc, the lower edge 1 of the camera field is op, the angle cop is 50 ° of half the field size, the angle pos is the sun avoidance angle, and 34 °. When the season changes, for example, the incident direction 2om of the sun is 23.4 degrees relative to the incident direction 1on until winter, then according to the geometric relationship, cos (++com) =cos (++con) ×cos (++com), the carried-in data have ++com of 84.5 degrees.
The angle of the camera lower edge 2 to the optical axis is calculated below. Assuming that co length is 1, cp length is tan50, cn length is tan84, mn length is tan 23.4X1/cos (84), qp length is tan 23.4X1/cos (84). Times.tan 50/tan84; the op length is 1/cos50, then the +.qop is 18.43. According to the geometric relationship of cos < coq=cos < cop×cos < qop, the angle coq=52.42 degrees can be obtained. At the moment, the angle between the incident direction of the sun and the edge of the view field of the camera is qom =84.5-52.4=32 degrees, and the maximum evasion 34 degrees change is not great when the camera is in the spring, so that the one-dimensional turntable is used for one-way adjustment, the one-way adjustment is completely feasible, the influence of seasons is avoided, and the evasion angle is 32 degrees at the maximum.
What is not described in detail in the present specification is a well known technology to those skilled in the art.
Although the present invention has been described in terms of the preferred embodiments, it is not intended to be limited to the embodiments, and any person skilled in the art can make any possible variations and modifications to the technical solution of the present invention by using the methods and technical matters disclosed above without departing from the spirit and scope of the present invention, so any simple modifications, equivalent variations and modifications to the embodiments described above according to the technical matters of the present invention are within the scope of the technical matters of the present invention.
Claims (11)
1. The photoelectric detection system for the GEO satellite omnidirectional 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 of the GEO satellite, which are perpendicular to the GEO track surface, 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 track surface; the visual fields of the six visible light cameras maximally cover 360-degree stereoscopic space around the GEO satellite;
the four turntables control the four visible light cameras to avoid direct solar radiation 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 always cover the earth;
the image processing module judges whether a target needing warning exists or not according to an optical image acquired by a visible light camera and an ultraviolet image acquired by a solar blind ultraviolet camera;
the angle adjusting function of the turntable is utilized, so that the angle between the upper edge pointing direction of the visual field of the visible light camera and the sun or the angle between the lower edge pointing direction 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 visual field edge of the camera, namely, the upper edge and the lower edge 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;
for any visible light camera positioned on the edge, along with the position and angle change of the satellite and the sun, when the included angle between one camera view field edge pointed by the optical axis of the visible light camera and the adjacent satellite surface is smaller than 1 degree, the optical axis pointing of the visible light camera is adjusted, so that the included angle between the camera view field edge and the incident direction of the sun is the sun avoidance angle.
2. The system of claim 1, wherein each visible camera has a half field angle of 50 °.
3. The photoelectric detection system for the omnidirectional alarm of the GEO satellite according to claim 2, wherein an optical detector is selected according to a half field angle, a detection distance and a target characteristic of each visible light camera, and the sensitivity of the optical detector reaches 5 sampsonies and more.
4. The photoelectric detection system for the omnidirectional alarm of the GEO satellite according to claim 1, wherein when judging whether an object to be alerted exists, the star point and the image noise point in the optical image are removed according to whether the detected object moves.
5. The photoelectric detection system for omni-directional warning of GEO satellite according to claim 1, wherein the detection probability and the working distance of the visible light camera are improved by increasing the exposure time when judging whether the target requiring warning exists.
6. The system of any one of claims 1-5, wherein the maximum solar avoidance angle field of view is 34 ° when the turntable is used to control the visible camera to avoid direct solar radiation.
7. The photoelectric detection system for the GEO satellite omni-directional alert according to one of claims 1 to 5, wherein the field of view of the solar blind ultraviolet camera optical system is 18 ° x 18 °.
8. The photoelectric detection system for omni-directional alarming of a GEO satellite according to 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.
9. The photoelectric detection system for GEO satellite omni-directional alerting according to claim 1, wherein when judging whether an object requiring alerting exists or not, when the gray scale of the detected object is 4 times or more the gray scale of the found time, the approaching satellite of the detected object is judged.
10. The photoelectric detection system for the GEO satellite omni-directional alert according to claim 1, wherein the moving object is confirmed by using a tailing phenomenon occurring in the moving object exposed for a long time, and the star point object is directly removed by star map recognition.
11. A photoelectric detection method based on the photoelectric detection system for GEO satellite omni-directional alerts according to any of claims 1 to 5, characterized by comprising the following steps:
s1, equivalent a GEO satellite to be a cuboid, and respectively installing four visible light cameras on four edges of the GEO satellite, which are perpendicular to a GEO track surface; mounting two visible light cameras on two surfaces parallel to the GEO-track surface; the visual fields of the six visible light cameras maximally cover 360-degree stereoscopic space around the GEO satellite;
s2, controlling four visible light cameras on the edge to avoid direct solar radiation 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 field of view of the solar blind ultraviolet camera to always cover the earth;
s4, judging whether a target needing warning exists or not according to the optical images acquired by the six visible light cameras and the ultraviolet images acquired by the at least one solar blind ultraviolet camera.
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