Radar system star calibration device and calibration method based on low-light-level television imaging

Abstract

The present invention relates to a radar system star calibration device and calibration method based on low-light-level television imaging. The device comprises a continuous zoom lens assembly 1, a low-light-level CCD group 2, a shell 3, a cover plate 4, a comprehensive processing board 5, a window assembly 6, etc., wherein the shell 3 is an assembly body, and the remaining functional components are directly or indirectly fixed inside or on the surface of the shell 3. The present invention uses a wide-band, large-magnification continuous zoom lens assembly 1 and a high-sensitivity, wide-dynamic-range low-light-level CCD group 2 to perform imaging tracking measurement on weak star targets, and uses built-in automatic ephemeris, radar longitude and latitude, time system time, etc. to calculate the errors between the theoretical values ​​and measured values ​​of the star observation azimuth and elevation angle, and then establishes a mathematical model to obtain various calibration parameters such as the zero value of the radar system angle, the non-horizontal of the large plate, and the non-orthogonal elevation azimuth, thereby assisting the radar to achieve rapid calibration. The device has the advantages of simple structure, high degree of automation, high calibration efficiency, etc., and has broad application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of optoelectronic equipment, and in particular to a star calibration device and a calibration method for a radar system based on low-light-level television imaging. Background Art

[0002] When the radar system is working, its own position error must be calibrated first. The commonly used calibration scheme is to manually aim the radar to point to multiple standard points with known real coordinates, and then manually calculate the deviation between the standard point and the radar encoder value when the radar points to the standard point, thereby obtaining various errors such as angle zero value, non-horizontal disk, non-orthogonal pitch and azimuth, and finally realizing the calibration of the radar system. Analysis shows that this scheme has many problems, such as low calibration accuracy, low degree of automation, and long time consumption. More importantly, the standard points are usually fixed in the test field, which makes the radar system inconvenient to use in the field.

[0003] Star calibration refers to determining the attitude and position of spacecraft, radar antennas and other equipment by observing the position and movement of celestial bodies. This technology has high application value in aerospace, optical measurement and other fields, and has good positioning accuracy and orientation capabilities. At present, research on star calibration technology has made certain progress at home and abroad. For example, NASA and ESA have widely used star calibration technology in space missions and are constantly upgrading and improving the technology.

[0004] Based on the above situation, we try to calibrate the radar system using stellar calibration technology to solve many problems such as the low efficiency and limited accuracy caused by the traditional calibration method relying on manual observation and data analysis. Summary of the invention

[0005] One of the purposes of the present invention is to provide a star calibration device for a radar system based on low-light-level television imaging, which includes a coaxially arranged continuous zoom lens assembly 1 and a low-light-level CCD group 2. The continuous zoom lens assembly 1 includes a coaxially and sequentially dispersed front fixed group 1-1, a zoom group 1-2, a compensation group 1-3, a rear fixed group 1-5, and a rear focusing group 1-4 inserted in the rear fixed group 1-5.

[0006] Furthermore, the front fixed group 1-1 includes a meniscus lens a1, a biconvex lens a2, a meniscus lens a3, a meniscus lens a4, and a meniscus lens a5 which are coaxially arranged in sequence, wherein the concave surface of the meniscus lens a1 is bonded to one of the convex surfaces of the biconvex lens a2, the other convex surface of the biconvex lens a2 is closely attached to the convex surface of the meniscus lens a3, the concave surface of the meniscus lens a3 is bonded to the convex surface of the meniscus lens a4, and the convex surface of the meniscus lens a5 is closely attached to the concave surface of the meniscus lens a4.

[0007] Furthermore, the zoom group 1-2 includes a biconcave lens b1, a biconvex lens b2, and a biconcave lens b3 arranged coaxially in sequence, wherein one of the concave surfaces of the biconcave lens b1 is closely attached to one of the convex surfaces of the biconvex lens b2, and the other convex surface of the biconvex lens b2 is bonded to one of the concave surfaces of the biconcave lens b3.

[0008] Furthermore, the compensation group 1-3 includes a biconvex lens c1, a biconcave lens c2, and a biconcave lens c3 arranged coaxially in sequence, wherein one of the convex surfaces of the biconvex lens c1 is bonded to one of the concave surfaces of the biconcave lens c2, and the other concave surface of the biconcave lens c2 faces the biconcave lens c3.

[0009] Further, the rear fixed group 1-5 includes a biconvex lens e1, a concave-convex lens e2, a biconvex lens e3, a concave-convex lens e4, a biconcave lens e5, a biconvex lens e6, a concave-convex lens e7, a biconvex lens e8, and a concave-convex lens e9 arranged coaxially in sequence, wherein one of the convex surfaces of the biconvex lens e1 is bonded to the concave surface of the concave-convex lens e2, the convex surfaces of the biconvex lens e3 and the concave-convex lens e4 are closely attached together and the other surfaces of each are closely attached to the biconvex lens e2 and the biconcave lens e5, one of the concave surfaces of the biconcave lens e5 is bonded to one of the convex surfaces of the biconvex lens e6, the convex surface of the concave-convex lens e7 faces the biconvex lens e6 and the two are spaced apart, the concave surface of the concave-convex lens e7 faces the biconvex lens e8, and the convex surface of the concave-convex lens e9 is closely attached to the biconvex lens e8.

[0010] Furthermore, the rear focusing group 1-4 includes a biconcave lens d1, and the biconcave lens d1 is inserted between the biconvex lens e6 and the meniscus lens e7 of the rear fixed group 1-5.

[0011] Furthermore, the working band of the continuous zoom lens assembly 1 is 0.4 μm to 1.0 μm, the focal length is 95 mm to 1230 mm, F#11.2, and the optical aperture is 110 mm.

[0012] Furthermore, the device type of the low-light CCD group 2 is: 1 / 2″ CCD sensor, pixel size: 8.6μm×8.3μm, effective pixel: 752×582, TV standard: PAL, minimum illumination: 0.0003lx (F1.4), image resolution: 720×576, signal-to-noise ratio: ≥46dB.

[0013] Furthermore, the device also includes a housing 3 , the continuous zoom lens assembly 1 and the low-light CCD group 2 are both fixed inside the housing 3 , and the continuous zoom lens assembly 1 passes through the housing 3 .

[0014] Furthermore, the device also includes a window assembly 6 fixed on the shell 3, and the window assembly 6 includes a motor, a rotating shaft, and a sun visor. The sun visor is connected to the motor through the rotating shaft and is driven by the motor to open or block the continuous zoom lens assembly 1.

[0015] Furthermore, the device also includes an integrated processing board 5, and the continuous zoom lens assembly 1 and the low-light CCD group 2 are both connected to the integrated processing board 5 and controlled by it.

[0016] The second object of the present invention is to provide a method for calibrating a radar system using the above-mentioned device, comprising the following steps: aiming the device at the sky and selecting a star as an observation target, using the built-in automatic ephemeris, radar longitude and latitude, and time system time of the device to calculate the observation azimuth A0 and elevation E0 of the star, thereby guiding the radar to point to a designated position to capture and track the star, measuring and recording the device's code disk azimuth A1, elevation E1 and star miss amount X, Y, thereby calculating the measured azimuth A0' and elevation E0' of the star, comparing the errors of the calculated theoretical values ​​of the star observation azimuth and elevation with the measured values, combining mathematical models to solve errors such as angle zero value, non-horizontal large disk, and non-orthogonal elevation and azimuth, and finally outputting the star calibration result.

[0017] Compared with the prior art, the advances of the present invention are mainly reflected in the following aspects: (1) The present invention utilizes the principle of low-light-level television imaging to achieve the purposes of automatic tracking, measurement, and calibration of stars during the day and night, thereby assisting the radar system in rapid and accurate automatic calibration under field conditions; (2) The device has the ability to detect third-magnitude stars under a clear night sky, with a star calibration accuracy of less than 10", and a star calibration time of less than 15 minutes. It can be used not only for the calibration of radar systems, but also for other optical measurement equipment, and has broad application prospects; (3) The device has the advantages of simple structure, high degree of automation, and high calibration efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a stereoscopic image of the star calibration device of the radar system based on low-light-level television imaging.

[0019] Figure 2 for Figure 1 A top view and a partial cross-sectional view of the left end of the device.

[0020] Figure 3 This is an optical system diagram of a continuous zoom lens assembly.

[0021] Figure 4 A cross-sectional view of a continuous zoom lens assembly.

[0022] Figure 5 This is the radar system calibration flow chart.

[0023] Figure numerals: 1 continuous zoom lens assembly, 1-1 front fixed group, 1-2 zoom group, 1-3 compensation group, 1-4 rear focusing group, 1-5 rear fixed group; 2 low light CCD group; 3 housing; 4 cover plate; 5 integrated processing board; 6 window assembly. DETAILED DESCRIPTION

[0024] In order to enable those skilled in the art to fully understand the technical solutions and beneficial effects of the present invention, the following is further described in detail in conjunction with specific embodiments and drawings. It should be emphasized that the embodiments listed below are only preferred implementations of the present invention and do not constitute any limitation to the present invention. Simple improvements or replacements made without departing from the main purpose of the present invention will still fall within the scope of protection of the present invention.

[0025] The appearance of the radar system star calibration device based on low-light-level television imaging provided by the present invention is as follows: Figure 1-2 As shown, it is composed of a continuous zoom lens assembly 1, a low-light CCD group 2, a housing 3, a cover plate 4, a comprehensive processing board 5 and a window assembly 6. The low-light CCD group 2 and the continuous zoom lens assembly 1 are coaxially fixed inside the housing 3 from left to right, the cover plate 4 is located on the upper part of the housing 3, and the window assembly 6 is fixed on the cover plate 4 and close to the right end of the housing 3. The window assembly 6 includes a sunshade, and the lens is switched between open and closed states by rotating the sunshade to protect the optical elements inside the housing. The comprehensive processing board 5 is fixed on the bottom plate of the continuous zoom lens assembly 1, which mainly realizes the functions of power supply communication, video tracking, control of the continuous zoom lens assembly and interstellar calibration.

[0026] like Figure 3-4 As shown, the continuous zoom lens assembly 1 is composed of a front fixed group 1-1, a zoom group 1-2, a compensation group 1-3, a rear focusing group 1-4, and a rear fixed group 1-5 arranged coaxially. The front fixed group 1-1 includes a concave-convex lens a1, a biconvex lens a2, a concave-convex lens a3, a concave-convex lens a4, and a concave-convex lens a5 arranged from left to right, wherein the concave-convex lens a1 and the biconvex lens a2, and the concave-convex lens a3 and the concave-convex lens a4 are bonded together. The zoom group 1-2 includes a biconcave lens b1, a biconvex lens b2, and a biconcave lens b3, wherein the biconvex lens b2 and the biconcave lens b3 are bonded together. The compensation group 1-3 includes a biconvex lens c1, a biconcave lens c2, and a biconcave lens c3, wherein the biconvex lens c1 and the biconcave lens c2 are bonded together. The rear fixed group 1-5 includes a biconvex lens e1, a concave-convex lens e2, a biconvex lens e3, a concave-convex lens e4, a biconcave lens e5, a biconvex lens e6, a concave-convex lens e7, a biconvex lens e8, and a concave-convex lens e9, wherein the biconvex lens e1 is bonded to the concave-convex lens e2, and the biconcave lens e5 is bonded to the biconvex lens e6. The rear focusing group 1-4 includes a biconcave lens d1, which is located between the biconvex lens e6 and the concave-convex lens e7.

[0027] The positional relationship of each lens in the continuous zoom lens assembly 1 is as follows: Figure 3-4 Its optical parameters are shown in Table 1 below:

[0028] Table 1 Parameter characteristics of each lens of the continuous zoom lens assembly

[0029] Original drawing number Curve radius (mm) Thickness(mm) Material a1 -154，-101 4.5 H-LAK53A a2 -101，291 12.6 H-FK61B a3 -169，-59 4.5 H-LAF10LA a4 -59，-431 12.6 H-FK61B a5 -56.7，-151.7 10.8 H-FK61B b1 1048.1，-69 3.1 H-ZLAF69A b2 -44，177 6.7 H-ZF52GT b3 177，-28.2 2.1 H-ZF52GT c1 -279.3，17 2.6 H-ZF52GT c2 17，-71 1.4 H-ZF52GT c3 23.4，-70.3 3.1 H-ZF52GT d1 14，-119.9 1.5 H-LAK4L e1 -20，19.1 9.5 H-FK61B e2 19.1，103 1.6 H-LAK12 e3 -27.2，37 5.7 H-FK61B e4 21.8，55 2.6 H-LAK12 e5 29.9，-19 1.4 H-ZLAF69A e6 -19，300.6 7.3 H-FK61B e7 27.1，16.1 1.4 H-QK3 e8 -44.3，27.2 4.2 H-FK61B e9 10.1，24.4 5.8 H—FK61B

[0030] The optical system characteristic parameters of the continuous zoom lens assembly 1 are as follows: working band 0.4μm~1.0μm, focal length 95mm~1230mm, F#11.2, optical aperture 110mm.

[0031] The continuous zoom lens assembly 1 has the characteristics of wide band and large zoom ratio, and is mainly used to obtain optical images of star targets. According to the optical characteristics of stars under day and night conditions, the optical system of the continuous zoom lens assembly 1 is designed as a long focal length optical system, wherein the long focal length can reduce the instantaneous field of view of the system, and the reduced field of view reduces the background intensity entering the detector. As a point target, the star target is small, so the target intensity basically does not change, thereby improving the contrast between the star and the background, and further improving the detection efficiency and reliability of the star. If the field of view is too small, the number of stars entering the field of view will be reduced, which will reduce the search efficiency of the star and is not conducive to the search and tracking of aerial targets. In order to ensure the detection of stars under the strong light background during the day, the continuous zoom lens assembly 1 is designed for a wide spectrum, and the spectral range is 0.4μm to 1.0μm.

[0032] In order to strictly control the matching tolerance of each set of moving mirror frames and mirror barrels, the mirror barrels are ground first during processing, and the moving mirror frames are ground based on the mirror barrels during assembly to ensure the clearance. During the processing of key parts, a cyclic heat treatment process is adopted to eliminate material stress and processing stress, effectively ensuring the dimensional stability of key parts. The above measures ensure the consistency of the optical axis and ensure that the target will not be lost when tracking the star target point.

[0033] The low-light CCD group 2 includes a detector and a back-end processing circuit board. The high-sensitivity, wide dynamic range low-light CCD group 2 is mainly used for star detection and identification. The main factor affecting star identification at night is the brightness of the star. The illumination of a 3rd magnitude star reaching the earth's surface in a clear night sky is 10 -7 Lux, according to the discussion in "Optoelectronic Devices (Theory and Fundamentals)", the illumination of a star of magnitude m falling on the imaging target and the illumination formed on the surface of the earth are calculated according to the following formula:

[0034]

[0035] d=1.22λF

[0036]

[0037] In the above formula: m in the m magnitude is 3; E 地 is the illumination formed by a 3rd magnitude star on the surface of the earth; D is the lens aperture, D=0.11m; d is the radius of the Airy disk; F is the lens F number, F=11.5; λ is the wavelength, λ=0.88um.

[0038] The illumination E of the target falling on the CCD target surface A Calculated according to the following formula:

[0039]

[0040] In the above formula: E0 is the target illumination; ρ is the target reflectivity, and for the telescope ρ is taken as 0.12; τ1 is the transmittance of the optical system, and the transmittance of the optical system τ1=0.8; τ2 is the atmospheric transmittance; D / f is the relative aperture, and D / f is taken as 0.125.

[0041] τ2 is calculated according to the following formula:

[0042]

[0043] According to the formula, when detecting a 3rd magnitude star at night, the illumination falling on the CCD target surface is about 2Lux.

[0044] During the day, due to the strong sky background, the dim and small star targets are submerged in the bright sky background. In addition, due to the interference of atmospheric turbulence, the detection and identification of stars are weak targets against the bright background. Therefore, the detector should have a low-light detector with a wide dynamic range and high quantum efficiency. Taking into account the difference in radiation wavelengths between the sky background and the star targets, the detector should have a good sensitivity in the near-infrared band. The main characteristic parameters of the high-sensitivity, wide-dynamic-range low-light CCD group 2 are: device type: 1 / 2″CCD sensor; pixel size: 8.6μm×8.3μm; effective pixel: 752×582; TV format: PAL; minimum illumination: 0.0003lx (F1.4); image resolution: 720×576; signal-to-noise ratio ≥46dB; power consumption: 2W; power supply: 12V±10%.

[0045] The housing 3 is a rectangular parallelepiped, and the low-light CCD group 2 is fixed at the left end inside the housing 3. The left end of the continuous zoom lens assembly 1 is opposite to the low-light CCD group 2, and its right end is fixed in the circular hole on the housing 3, and a sealing ring is provided at the circular hole for sealing. The cover plate 4 is fixed on the top of the housing 3, and a window assembly 6 is fixed at the right end of the cover plate 4. The housing 3, the cover plate 4, and the window assembly 6 are all made of aviation aluminum alloy materials with high specific strength, and the surface is anodized, and the exposed surface is also sprayed with protective coating to prevent corrosion such as salt spray.

[0046] The integrated processing board 5 (such as a microprocessor or a microcomputer) is electrically connected to the continuous zoom lens assembly 1, the low-light CCD group 2, the window assembly 6, etc., for power supply communication, video tracking and control of the continuous zoom assembly. The integrated processing board 5 mainly uses the continuous zoom lens group 1 and the low-light CCD group 2 to provide a real-time image of the target. After searching and finding the target in a large range through a large and medium field of view, it switches to a small field of view with a large magnification to enlarge the target, and selects manual / automatic capture of the target through the control software. When the target is successfully captured, it enters the image tracking mode. Using algorithms such as contrast tracking or correlation tracking, the deviation of the target in the image relative to the center of the sensor field of view in the X and Y directions is calculated, and the target angular position is obtained in real time through the offset and the angular position of the radar servo turntable.

[0047] The window assembly 6 includes a DC micro-motor assembly and a sun visor movement assembly, and the DC micro-motor drives the sun visor to rotate to achieve the blocking and opening of the lens window. The window assembly 6 can effectively prevent the CCD from being damaged, and can also prevent the objective lens from being eroded by water vapor, salt spray and mold.

[0048] The method for using the radar system star calibration device based on low-light-level television imaging provided by the present invention is as follows:

[0049] Step 1: Power on and start

[0050] The system is powered on, all parts are powered on and the control software is started.

[0051] Step 2: Power-on self-test

[0052] After the system is powered on, check the status of each component to confirm that the visible light imaging component 1, low light CCD group 2, integrated processing board 5, etc. are in normal status. If the self-check passes, proceed to the next step, otherwise check and eliminate the fault.

[0053] Step 3: Star Selection

[0054] Aim the device at the sky and select several stars with similar magnitudes and evenly distributed in the four quadrants of the field of view as observation targets;

[0055] Step 4: Star position calculation

[0056] According to the device's built-in automatic ephemeris, radar longitude and latitude, and time, calculate the star observation azimuth A0 and elevation E0;

[0057] Step 5: Capture the Star

[0058] According to the calculated observation azimuth angle A0 and elevation angle E0, the radar is guided to point to the designated position, and the star is captured and tracked after it enters the field of view;

[0059] Step 6: Measuring the Stars

[0060] Record the code disk azimuth angle A1, pitch angle E1 and star miss distance X, Y;

[0061] Step 7: Get the measured value

[0062] According to the azimuth angle A1, elevation angle E1 and star miss distance X, Y measured by the device, the measured azimuth angle A0' and elevation angle E0' of the star are calculated;

[0063] Step 8: Calculate the error

[0064] Compare the calculated theoretical values ​​of the star observation azimuth and elevation angles with the measured values; after this step is completed, proceed to the next step, or repeat steps 3 to 8 to measure the next star;

[0065] Step 9: Calculate radar errors

[0066] Through the errors between the theoretical and measured values ​​of the azimuth and elevation angles of star observation and the mathematical model established using various parameters of stars, various errors such as angle zero value, non-horizontal disk, non-orthogonal elevation and azimuth are calculated, and finally the star calibration results are output and saved.

[0067] The present invention utilizes a wide-band, large-variable-ratio continuous zoom lens assembly and a high-sensitivity, wide-dynamic-range low-light-level CCD group to perform imaging tracking measurement on weak star targets, and automatically calculates the errors between the theoretical values ​​of the star observation azimuth and elevation angle and the measured values ​​according to the built-in automatic ephemeris of the equipment, the longitude and latitude of the radar, and the time of the time system, and obtains various calibration parameters such as the zero value of the radar system angle, the non-horizontal state of the large disk, and the non-orthogonality of the elevation and azimuth, thereby assisting the radar in realizing rapid calibration.

Claims

1. A radar system star calibration device based on low-light-level television imaging, characterized in that: The device comprises a coaxially arranged continuous zoom lens assembly (1) and a low-light CCD group (2), wherein the continuous zoom lens assembly (1) comprises a coaxially and sequentially arranged front fixed group (1-1), a magnification group (1-2), a compensation group (1-3), a rear fixed group (1-5), and a rear focusing group (1-4) inserted in the rear fixed group (1-5).

2. The device according to claim 1, characterized in that: The front fixed group (1-1) includes a concave-convex lens a1, a biconvex lens a2, a concave-convex lens a3, a concave-convex lens a4, and a concave-convex lens a5 which are coaxially arranged in sequence.

3. The device according to claim 1, characterized in that: The zoom group (1-2) comprises a biconcave lens b1, a biconvex lens b2, and a biconcave lens b3 which are coaxially arranged in sequence.

4. The device according to claim 1, characterized in that: The compensation group (1-3) includes a biconvex lens c1, a biconcave lens c2, and a biconcave lens c3 which are coaxially arranged in sequence.

5. The device according to claim 1, characterized in that: The rear fixed group (1-5) includes a biconvex lens e1, a concave-convex lens e2, a biconvex lens e3, a concave-convex lens e4, a biconcave lens e5, a biconvex lens e6, a concave-convex lens e7, a biconvex lens e8, and a concave-convex lens e9 which are coaxially arranged in sequence.

6. The device according to claim 5, characterized in that: The rear focusing group (1-4) comprises a biconcave lens d1, and the biconcave lens d1 is inserted between the biconvex lens e6 and the meniscus lens e7 of the rear fixing group (1-5).

7. The device according to claim 1, characterized in that: The working band of the continuous zoom lens assembly (1) is 0.4 μm to 1.0 μm, the focal length is 95 mm to 1230 mm, F#11.2, and the optical aperture is 110 mm. The device type of the low-light CCD group (2) is: 1 / 2″ CCD sensor, pixel size: 8.6 μm×8.3 μm, effective pixel: 752×582, television standard: PAL, minimum illumination: 0.0003 lx (F1.4), image resolution: 720×576, signal-to-noise ratio: ≥46 dB.

8. The device according to claim 1, characterized in that: The device also comprises a housing (3) and a window assembly (6) fixed on the housing (3); the continuous zoom lens assembly (1) and the low-light CCD group (2) are both fixed inside the housing (3); the window assembly (6) comprises a motor, a rotating shaft, and a sunshade; the sunshade is connected to the motor via the rotating shaft and is driven by the motor.

9. The device according to claim 1, characterized in that: The device also comprises a comprehensive processing board (5), and the continuous zoom lens assembly (1) and the low-light CCD group (2) are both connected to the comprehensive processing board (5) and controlled by it.

10. A method for calibrating a radar system using the device according to any one of claims 1 to 9, characterized in that The method comprises the following steps: aiming a device at the sky and selecting a star as an observation target, using the built-in automatic ephemeris, radar longitude and latitude, and time system time of the device to calculate the observation azimuth angle A0 and elevation angle E0 of the star, thereby guiding the radar to point to a designated position to capture and track the star, measuring and recording the device's code disk azimuth angle A1, elevation angle E1 and star miss distances X and Y, thereby calculating the measured azimuth angle A0' and elevation angle E0' of the star, comparing the errors of the calculated observation azimuth angle and elevation angle theoretical values ​​with the measured values ​​of the stars, solving the errors of angle zero value, large disk non-horizontal, elevation azimuth non-orthogonality, etc. in combination with a mathematical model, and finally outputting the star calibration result.

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