Daytime celestial body detecting device

[0033] like figure 1 , 2 , 3, the present invention consists of a hood 1, a protective glass 2, a flat glass 3, a reflector 4, a two-piece compensation mirror group 5, a main mirror 6, a filter turntable and its adjustment mechanism 7, a polarizer and its The adjusting mechanism 8 , the CCD camera 9 , the heat dissipation channel 10 , and the chassis 11 are composed. Among them, the protective glass 2 , the flat glass 3 , the reflecting mirror 4 , the two-piece compensation mirror group 5 , and the main mirror 6 form a symmetrical fold-back optical system. The hood 1 and the symmetrical fold-back optical system are installed in the same lens barrel, and the lens barrel is installed on the chassis 11. The chassis 11 is equipped with a filter and its adjustment mechanism 7, a polarizer and its adjustment mechanism 8, and a CCD camera 9. , heat dissipation channel 10 .

[0034] The hood 1 is installed at the front of the system. When measuring stars in the daytime, since the background is the sky, the stray light is very strong, which will reduce the modulation transfer function of the system, reduce the level of the entire picture, and deteriorate the clarity. stray light spots. Therefore, it is particularly important to use the light shield 1 to suppress stray light.

[0035]Behind the hood 1 is a symmetrical fold-back optical system, which is mainly composed of a protective glass 2 , a flat glass 3 , a reflector 4 , a two-piece compensation mirror group 5 , and a main mirror 6 . The first surface of the main mirror 6 is a transmission surface, and the second surface is a reflection surface. The reflector 4 is attached to the flat glass 3, so that the fixed effect can be achieved through the flat glass 3, and the application of mechanical structures such as flanges that block light can be avoided. The compensation lens group 5 composed of two lenses can be adjusted during installation to ensure the installation effect.

[0036] The optical system has a sufficiently long back focal length, so that a filter and an adjustment mechanism 7 and a polarizer and an adjustment mechanism 8 can be installed between the optical system and the CCD camera 9 . The filter adjustment mechanism and the polarizer adjustment mechanism can be rotated under the driving of the motor.

[0037] The system can adjust the focus by moving the CCD camera 9, and adopts stepper motor open-loop control. Considering that the CCD camera 9 requires refrigeration during operation, and the CCD camera 9 selected in the present invention has a fan itself, a heat dissipation channel 10 is designed to guide the heat generated by the camera to the outside of the chassis to avoid heat accumulation in the chassis. cause interference.

[0038] Figure 4 This is the structure diagram of the optical system of the present invention. During the design and processing process, the unbiased characteristics of the lens and the entire optical system must be guaranteed. To this end, a symmetrical fold-back optical system is used. The incident light enters the symmetrical fold-back optical system, passes through the protective glass 2 and the flat glass 3 in sequence, is transmitted on the first surface of the main mirror 6, and is reflected on the second surface. The mirror group 5 is emitted from the symmetrical reentrant optical system, and the emitted light passes through the filter and adjustment mechanism 7 and the polarizer and adjustment mechanism 8 to adjust the energy of the target and background light, and finally reaches the image plane of the CCD camera 9 for imaging. The wavelength band of the optical system is 450-1000nm, and the response band of the CCD camera is 400-1080nm. These are selected based on the spectral properties of the target. The central wavelength of the optical system is 700 nm, which is close to the spectral peak of stars in the background of the daytime sky. The entrance pupil diameter of the optical system is 200mm, the focal length is 800mm, and the F number is 4. The glass materials are all made of N-BK7, which has good chemical and mechanical properties and is cheap. As shown in Table 1:

[0039] Table 1. Lens parameters and detector parameters

[0040]

[0041] Figure 5 , Image 6 For the image quality analysis of the optical system. It is the modulation transfer function diagram and the dot diagram of the optical system, respectively. from Figure 5 It can be seen that at 60 line pairs/mm, the modulation transfer function MTF of the system is greater than 0.55, which is very close to the diffraction limit, which can ensure a good imaging quality; from Image 6 It can be seen that the root mean square radius RMS is less than 3.236mm in all fields of view, and the spot diagram is very circular, indicating that both coma and astigmatism are very small. from Figure 5 , Image 6 It can be seen that the optical system can fully meet the detection requirements.

[0042] Figure 7 It is the change curve of the relative irradiance value of the background and the target with the wavelength at a certain time during the day. The dotted line f(λ) represents the change curve of the relative irradiance value of the background with the wavelength λ in the range of 0.1μm to 1.1μm; the solid line g(λ) represents the relative irradiance value of the target with the wavelength λ. Curve. from Figure 7 It can be seen that for the cloudless sky during the day at this time, the background light is mainly short-wave, its peak appears at a wavelength λ of about 0.5 μm, and its continuous spectral curve decreases faster from the peak to the longer wavelength band. Fast, beyond the wavelength of 0.9 μm, the spectral energy is already very low. However, the relative energy of the target is different, its wavelength is longer, and its peak appears near the wavelength of 0.8μm. In this way, in the detection of stars in the daytime, if a filter is used to cut off the light at the wavelength of 0.6 μm or 0.7 μm, the signal-to-noise ratio can be significantly improved and the purpose of detection can be achieved.

[0043] Figure 8 It is a filter and adjustment mechanism 7, 12 is a filter, 13 is a gear, and 14 is a stepping motor. The filters are dimmed, and the stepper motor 14 is used to drive the gear 13, thereby driving the switching between different filters. There are zero-position signal and in-position signal on the optical filter, both of which are provided by the photoelectric pair tube.

[0044] The filter dimming is divided into 8 grades, and the filter transmittance and band are shown in Table 2 below:

[0045] Table 2 Bands and transmittances of filters

[0046]

[0047] As shown in Table 2, two types of filters are applied to the detection system, a colorless filter and a color filter. These two filters have four transmittances for selection, which are 98.5%, 50%, 25%, and 5% respectively. When detecting, the selection of filter transmission is based on the following two principles: ( 1) There should be enough light intensity; (2) To prevent CCD saturation.

[0048] The colorless filter (band 0.4-1.0μm) allows detection in the visible light range; the color filter (band 0.6-1.0μm) allows the application of spectral filtering to detect target stars in the background of the daytime sky.

[0049] Figure 9 Shown is the distribution of polarization states against a daytime sky background. Among them, D point is the sky vertex, F is the sun, A represents the opposite direction of the sun, C point is the maximum polarization value, G point, E point, B point are three neutral points, of which G point is in brewsterk Sex point, B point is babanet neutral point, B point is arago neutral point. like Figure 7 As shown, in the horizon of the sun, at the position (C) where the angle between the scattering surface and the incident light of the sun (F) is 90°, the observed polarization value is the largest, while in Babinet (E), Brewster ( G), Arago (A) neutral point is the zero polarization point, when the observation direction deviates from the sun (F) and reaches 90° (C), the observed polarization degree increases gradually in the visible and infrared spectral regions , after which the degree of polarization begins to decrease. The polarization state of the target star is theoretically zero, and its polarization degree is still very small after being scattered by the atmosphere.

[0050] Figure 10 It is a polarizer adjustment mechanism 8. 15 is a polarizer (using a linear vibrating plate), 16 is a driving wheel, 17 is a motor, and 18 is a driven wheel. The motor 17 drives the driven wheel 18 by driving the driving gear teeth 16, thereby realizing polarization. Rotation of sheet 15. The control range of the rotation angle of the polarizer is: 0°~180°, and the angle control resolution is 0.1°. Using the polarizer adjustment mechanism to rotate the polarizer 15 can not only measure the Stokes parameter S (I, Q, U, V) of the background according to the different polarization states of the target star and the background, and then know the polarization of the background light. information:

[0051] The angles of rotating polarizer 15 are respectively 0°, 45° and 90°, and the light intensity values ​​measured three times are respectively 1 1 , I 2 , I 3 ,but

[0052] I 1 = 1 2 ( I + Q ) I 2 = 1 2 ( I - Q ) I 3 = 1 2 ( I + U ) - - - ( 1 )

[0053] Because in the background of the sky during the day, the value of V is very small and can be approximated to 0, so there are

[0054] I = I 1 + I 2 Q = I 1 - I 2 U = I 1 + I 2 - 2 I 3 V = 0 - - - ( 2 )