Passive athermalized high resolution infrared camera for low earth orbit

Abstract

The synchronous orbit middle wave infrared catadioptric passive athermalization high-resolution remote sensing camera disclosed by the application belongs to the field of infrared earth remote sensing observation. The application is a synchronous orbit middle wave infrared catadioptric passive athermalization high-resolution space remote sensing camera, which comprises a Cassegrain double-reflection system, a rear six-piece spherical lens group, a field stop piece, a light path folding mirror, a cold stop and a detector. The application can obtain a large single scene wide ground pixel resolution space remote sensing camera image, and simultaneously realizes compensation for system thermal defocusing, passive athermalization imaging and correction of chromatic aberration in the infrared optical system by distributing the positive and negative focal lengths of the lenses in the infrared optical system. The passive athermalization imaging makes the system structure simple, and the thermal aberration correction in a wide temperature range can be realized without complex moving parts. The application has the advantages of high spatial resolution, wide coverage, all-day work, wide temperature working range and small chromatic aberration.

Description

Technical Field

[0001] The present invention relates to a medium-wave infrared catadioptric high-resolution space remote sensing camera running on a geosynchronous orbit and having a passive athermalization working mode, belonging to the field of infrared earth remote sensing observation. Background Art

[0002] Space-based Earth observation is a cutting-edge technology that utilizes advanced space optical remote sensing cameras to identify and acquire information about relevant targets. It also provides technical support for emergency response needs in disaster reduction, meteorology, earthquake management, forestry, environmental protection, and other industries. Visible light Earth observation is currently the most widely used and mature space remote sensing technology. Visible light optical systems receive energy from visible light reflected from the target object or emitted by the object itself. This means visible light observation can only be performed during daylight hours and is significantly affected by meteorological conditions in the target area. Infrared optical systems receive infrared radiation energy from the target object itself, overcoming the visible light system's dependence on time and enabling 24 / 7 operation. Furthermore, due to the excellent long-wavelength penetration capability, infrared systems can also conduct observations in adverse weather conditions such as fog and clouds.

[0003] In space-based infrared remote sensing camera applications, drastic temperature fluctuations pose a severe challenge to the system. Temperature fluctuations can alter the properties of various optical system components, such as the lens surface curvature radius, lens thickness, lens refractive index, and lens barrel length. These thermally induced changes can cause severe thermal defocus, degrading image quality, blurring images, and reducing contrast, ultimately impacting overall system performance. Therefore, athermalization technology is necessary to eliminate the effects of temperature.

[0004] Therefore, how to provide a space infrared remote sensing camera that has high spatial resolution, wide coverage area, all-day working mode, wide temperature working range and achromatic observation performance has become a key technical problem that needs to be solved urgently in this field. Summary of the Invention

[0005] The main purpose of the present invention is to provide a geosynchronous orbit medium-wave infrared catadioptric passive athermal high-resolution space remote sensing camera to obtain ground pixel resolution space remote sensing camera images under a large single-view width. At the same time, by allocating the positive and negative optical focal lengths of each lens in the infrared optical system, compensation for system thermal defocus is achieved, achieving passive athermal imaging, and taking into account the correction of chromatic aberration in the infrared optical system. The present invention has the advantages of high spatial resolution, wide coverage area, all-day operation, wide temperature operating range, and small chromatic aberration. The ground pixel resolution space remote sensing camera image under the large single-view width can achieve a ground pixel resolution of 200 meters.

[0006] The purpose of the present invention is achieved through the following technical solutions.

[0007] The present invention discloses a geosynchronous orbit medium-wave infrared catadioptric passive athermal high-resolution remote sensing camera. The camera comprises a Cassegrain double-reflector system, a rear six-element spherical lens assembly, a field stop, an optical folding mirror, a cold stop, and a detector. The Cassegrain double-reflector system utilizes a parabolic first primary reflector and a rotating hyperbolic second secondary reflector. The incident medium-wave infrared beam is reflected twice by the first primary reflector and the second secondary reflector to correct for spherical aberration. The Cassegrain double-reflector system provides the space remote sensing camera with a large optical aperture. The rear six-element spherical lens group primarily consists of the third, fourth, seventh, eighth, ninth, and tenth lenses. This group corrects chromatic aberration of the mid-wave infrared beam emitted by the Cassegrain double-reflector system through the distribution of optical power. The third, seventh, and ninth lenses are made of optical silicon, the fourth and eighth lenses are made of optical gallium arsenide, and the tenth lens is made of optical germanium. Passive athermal imaging is achieved by matching the refractive indices and expansion coefficients of these lenses. The field stop is the fifth element with a central aperture. The optical path is deflected by an optical folding mirror to reduce the size of the high-resolution space remote sensing camera. The cold stop is the detector's cold stop, corresponding to the eleventh lens. Made of optical germanium and made of flat glass, it is located at the exit pupil of the high-resolution space remote sensing camera. Matching the exit pupil with the detector's cold stop creates a cold stop effect that suppresses stray thermal radiation from the camera itself. The twelfth focusing imaging surface is the focusing imaging plane, where the detector is located.

[0008] To improve the passive athermal imaging effect, it is preferred to match the refractive index and expansion coefficient of the above-mentioned lenses to achieve passive athermal imaging. The implementation method is as follows:

[0009] In order to ensure the spherical aberration correction effect of the medium-wave infrared beam, the surface curvature radius of the first main reflector is -1434.25mm~-1431.45mm, the quadratic coefficient is -1.01~-0.99, the outer diameter of the main reflector is not less than 600mm, the central opening radius of the main reflector is 74~76mm, the distance from the second secondary reflector is 551.50mm~551.60mm, and the material is SiC; preferably, the surface curvature radius of the first main reflector is -1432.85mm, the quadratic coefficient is -1, the reflector aperture is 600mm in diameter, the central opening radius is 75mm, the distance from the second secondary reflector is 551.55mm, and the material is SiC.

[0010] In order to ensure the spherical aberration correction effect of the medium-wave infrared beam, the surface curvature radius of the second secondary reflector is -448.02mm~-447.22mm, the quadratic coefficient is -2.91~-2.89, the secondary reflector diameter is 144mm~146mm, the distance from the front surface of the third lens is 550.28mm~551.28mm, and the material is SiC; preferably, the surface curvature radius of the second main reflector is -447.62mm, the quadratic coefficient is -2.90, the secondary reflector diameter is 145mm, the distance from the front surface of the third lens is 550.78mm, and the material is SiC.

[0011] In order to ensure the correction effect of thermal aberration and chromatic aberration of the medium-wave infrared light beam, the thickness of the third lens is 18.33mm~18.37mm, the front surface curvature radius is 249.75mm~250.25mm, the rear surface curvature radius is 126mm~126.26mm, the distance from the front surface of the fourth lens is 41.10mm~41.18mm, and the material is optical silicon; preferably, the thickness of the third lens is 18.35mm, the front surface curvature radius is 250.00mm, the rear surface curvature radius is 126.13mm, the distance from the front surface of the fourth lens is 41.14mm, and the material is optical silicon.

[0012] In order to ensure the correction effect of thermal aberration and chromatic aberration of the medium-wave infrared light beam, the thickness of the fourth lens is 9.98mm~10.02mm, the front surface curvature radius is 121.99mm~122.23mm, the rear surface curvature radius is 203.27mm~203.67mm, the distance from the fifth field aperture is 52.96mm~53.04mm, and the material is gallium arsenide; preferably, the thickness of the fourth lens is 10.00mm, the front surface curvature radius is 122.11mm, the rear surface curvature radius is 203.47mm, the distance from the fifth field aperture is 53mm, and the material is gallium arsenide.

[0013] To suppress stray light outside the field of view, the fifth field stop is a circular mechanical element that also serves as a stray light suppressor. Its front and rear surfaces are both flat. The stop can be 0.8mm to 1.2mm thick, with an inner radius of 11.2mm to 11.4mm, an outer radius of 15mm to 16mm, and a distance from the sixth optical path folding mirror of 80.00mm to 80.50mm. It is made of aluminum alloy. Preferably, the stop is 1.00mm thick, with an inner radius of 11.3mm, an outer radius of 15.5mm, and a distance from the sixth optical path folding mirror of 80.25mm. It is made of aluminum alloy.

[0014] In order to significantly compress the volume of the optical system, the sixth plane reflector is a light path folding mirror. The thickness of the plane reflector can be 2.8mm~3.2mm, the diameter can be 56mm~60mm, the distance from the front surface of the seventh lens can be 119.95mm~120.05mm, and the material is microcrystalline glass; preferably, the thickness of the plane reflector can be 3mm, the diameter can be 58mm, the distance from the front surface of the seventh lens can be 120mm, and the material is microcrystalline glass.

[0015] In order to ensure the correction effect of thermal aberration and chromatic aberration of the medium-wave infrared light beam, the thickness of the seventh lens is 5.98mm~6.02mm, the front surface curvature radius is 424.22mm~425mm, the rear surface curvature radius is 285.61mm~286.21mm, the distance from the front surface of the eighth lens is 24.96mm~25.04mm, and the material is optical silicon; preferably, the thickness of the seventh lens is 6.00mm, the front surface curvature radius is 424.62mm, the rear surface curvature radius is 285.91mm, the distance from the front surface of the eighth lens is 25mm, and the material is optical silicon.

[0016] In order to ensure the correction effect of thermal aberration and chromatic aberration of the medium-wave infrared light beam, the eighth lens has a thickness of 11.98mm to 12.02mm, a front surface curvature radius of -3130.92mm to -3124.66mm, a rear surface curvature radius of 582.57mm to 583.73mm, a distance from the front surface of the ninth lens is 3.44mm to 3.48mm, and the material is gallium arsenide; preferably, the eighth lens has a thickness of 12.00mm, a front surface curvature radius of -3127.79mm, a rear surface curvature radius of 583.15mm, a distance from the front surface of the ninth lens is 3.46mm, and the material is gallium arsenide.

[0017] In order to ensure the correction effect of thermal aberration and chromatic aberration of the medium-wave infrared light beam, the thickness of the ninth lens is 13.14mm~13.18mm, the front surface curvature radius is -48.47mm~-48.37mm, the rear surface curvature radius is -74.80mm~-74.66mm, the distance from the front surface of the ninth lens is 2.98mm~3.02mm, and the material is optical silicon; preferably, the thickness of the ninth lens is 13.16mm, the front surface curvature radius is -48.42mm, the rear surface curvature radius is -74.73mm, the distance from the front surface of the tenth lens is 3.00mm, and the material is optical silicon.

[0018] In order to ensure the correction effect of thermal aberration and chromatic aberration of the medium-wave infrared light beam, the thickness of the tenth lens is 5.58mm~5.54mm, the front surface curvature radius is -75.13mm~-75mm, the rear surface curvature radius is -39.31mm~-39.23mm, the distance from the front surface of the eleventh lens is 37.98mm~38.02mm, and the material is optical germanium; preferably, the thickness of the tenth lens is 5.56mm, the front surface curvature radius is -75.06mm, the rear surface curvature radius is -39.27mm, the distance from the front surface of the eleventh lens is 38.00mm, and the material is optical germanium.

[0019] In order to achieve a 100% cold aperture effect, the eleventh lens is made of flat glass and serves as a cold screen. Its position coincides with the exit pupil of the camera system, its thickness is 4.98mm to 5.02mm, and its distance from the imaging surface is 54.98mm to 55.02mm. The material is optical germanium. Preferably, the eleventh lens has a thickness of 5mm, a distance from the imaging surface is 55mm, and is made of optical germanium.

[0020] The twelfth surface is a focusing imaging surface, and the optional specification is a medium-wave infrared cooling detector with a pixel size of 15 μm and a 1024×1024 pixel size.

[0021] The geosynchronous orbit medium-wave infrared catadioptric passive athermal high-resolution space remote sensing camera of the present invention has an operating orbit altitude of 36,000 km; an observation band of 3 μm to 5 μm; an observation field of view of 0.4°×0.4°; a system focal length of 2150 mm; a relative aperture of 1:3.58; a single-view width of 251 km×251 km; a ground pixel resolution of 251 m; a camera system lens group mass of only 0.52 kg; a total system length of less than 800 mm; and a detector pixel size of 15 μm.

[0022] The geosynchronous orbit medium-wave infrared catadioptric high-resolution space remote sensing camera of the present invention has a passive athermal working mode and can operate in a wide temperature range of -30°C to +50°C. The optical passive athermal technology adopted by the present invention has obvious advantages over mechanical passive athermal technology and electronic active athermal technology, such as simple structure, small physical size, no need for power supply, and good reliability.

[0023] The working method of the geosynchronous orbit medium-wave infrared catadioptric passive athermal high-resolution space remote sensing camera disclosed in the present invention is as follows:

[0024] The geosynchronous orbit medium-wave infrared (MWIR) catadioptric passive athermalized high-resolution space remote sensing camera detects MWIR light from the target. The incident MWIR beam is reflected twice by the first primary reflector and the second secondary reflector to correct for spherical aberration. The Cassegrain double-reflector system enables the camera to have a large optical aperture, improving sensitivity. In the rear six-element spherical lens assembly, by matching the glass refractive index, optical power, and expansion coefficient of the third, fourth, seventh, eighth, ninth, and tenth lenses, the MWIR beam emitted from the Cassegrain double-reflector system is corrected for thermal and chromatic aberration, enhancing image quality and performance close to the diffraction limit. The fifth field stop restricts the camera's field of view and acts as a stray light diaphragm to suppress stray light outside the field of view, improving the camera's signal-to-noise ratio. The sixth optical folding mirror deflects the imaging beam, significantly reducing the size of the remote sensing camera and conserving satellite platform space resources. Because the eleventh lens is made of flat glass and acts as a cold screen, its position coincides with the camera's exit pupil, achieving a 100% cold stop effect. This suppresses stray thermal radiation from the high-resolution space remote sensing camera itself, enabling passive athermalization of high-resolution space remote sensing imaging in geosynchronous orbit using medium-wave infrared catadioptric imaging.

[0025] Beneficial effects:

[0026] The medium-wave infrared catadioptric passive athermal high-resolution space remote sensing camera system of the present invention operates in a geosynchronous orbit at an altitude of 36,000 km. The beneficial effects that can be achieved in actual earth observation are as follows:

[0027] 1. This invention discloses a geosynchronous orbit medium-wave infrared (MWIR) catadioptric passive athermalized high-resolution space remote sensing camera. Due to its use of a front-mounted Cassegrain double-reflector system, the MWIR camera system has a lighter structure and more compact size compared to fully transmissive or off-axis fully reflective MWIR cameras. By using different optical glass to distribute and optimize optical power, thereby correcting for optical chromatic and thermal aberrations, the camera achieves a modulation transfer function greater than 0.27 across the entire field of view at a Nyquist spatial frequency of 33.33 lp / mm, achieving near-diffraction-limited imaging performance.

[0028] 2. This invention discloses a geosynchronous orbit medium-wave infrared (MWIR) passive athermalized, high-resolution space remote sensing camera. The MWIR camera system utilizes a catadioptric optical layout, enabling a focal length of 2150 mm. This is difficult to achieve with traditional fully transmissive MWIR remote sensing cameras. Furthermore, the excellent aberration correction capabilities of the rear lens assembly enable the camera to achieve a ground pixel resolution of 200 meters. This provides technical support and a source of raw data for emergency response needs in disaster reduction, meteorology, earthquake, forestry, environmental protection, and other industries.

[0029] 3. The present invention discloses a geosynchronous orbit medium-wave infrared catadioptric passive athermal high-resolution space remote sensing camera, which utilizes the optical focal length distribution between lenses to achieve passive thermal defocus compensation. The passive athermal design simplifies the system structure. Compared with the active athermal design, it does not require complex moving parts to achieve thermal aberration correction in a wide temperature range.

[0030] 4. The synchronous orbit medium-wave infrared catadioptric passive athermal high-resolution remote sensing camera disclosed in the present invention is capable of obtaining 200-meter-class ground pixel resolution space remote sensing camera images with a large single-view width. At the same time, by allocating the positive and negative optical focal lengths of each lens in the infrared optical system, it compensates for the thermal defocus of the system to correct thermal aberrations, achieves passive athermal imaging, and also takes into account the correction of chromatic aberration in the infrared optical system. On the basis of achieving the above-mentioned beneficial effects 1, 2, and 3, the present invention, through theoretical analysis and a large number of creative experiments, provides parameter ranges for improving spatial resolution, broadening coverage area, all-day operation, widening temperature operating range, and reducing chromatic aberration, as well as optimal optical structure parameters, so that the present invention has the advantages of high spatial resolution, wide coverage area, all-day operation, wide temperature operating range, and small chromatic aberration. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Optical structure diagram of the geosynchronous orbit medium-wave infrared catadioptric passive athermal high-resolution space remote sensing camera;

[0032] Figure 2 Spot diagram of a geosynchronous medium-wave infrared catadioptric passive athermalized high-resolution space remote sensing camera;

[0033] Figure 3 A graph showing the variation of the root mean square radius of the image plane diffuse spot with wavelength for a geosynchronous medium-wave infrared catadioptric passive athermal high-resolution space remote sensing camera.

[0034] Figure 4 A graph showing the variation of the root mean square radius of the image plane diffuse spot with the field of view of a geosynchronous orbit medium-wave infrared catadioptric passive athermal high-resolution space remote sensing camera.

[0035] Figure 5 Modulation transfer function curve of the geosynchronous orbit medium-wave infrared catadioptric passive athermal high-resolution space remote sensing camera in a 20°C environment;

[0036] Figure 6 A graph showing the energy fraction of the image plane surrounding circle of a geosynchronous orbit medium-wave infrared catadioptric passive athermal high-resolution space remote sensing camera as a function of radius.

[0037] Figure 7 Image wave aberration of a geosynchronous orbit medium-wave infrared catadioptric passive athermalized high-resolution space remote sensing camera at the edge of the field of view;

[0038] Figure 8 Field curvature and distortion aberration curves of a geosynchronous medium-wave infrared catadioptric passive athermalized high-resolution space remote sensing camera;

[0039] Figure 9 A graph showing how the root mean square radius of the image plane diffuse spot of a geosynchronous medium-wave infrared catadioptric passive athermal high-resolution space remote sensing camera changes with the system defocus.

[0040] Figure 10 Axial chromatic aberration curve of the geosynchronous orbit medium-wave infrared catadioptric passive athermalized high-resolution space remote sensing camera;

[0041] Figure 11 Magnification chromatic aberration curve of the geosynchronous orbit medium-wave infrared catadioptric passive athermalized high-resolution space remote sensing camera;

[0042] Figure 12 Modulation transfer function curve of the geosynchronous orbit medium-wave infrared catadioptric passive athermal high-resolution space remote sensing camera in a -30°C environment;

[0043] Figure 13 Modulation transfer function curve of the geosynchronous orbit medium-wave infrared catadioptric passive athermal high-resolution space remote sensing camera in a 50°C environment;

[0044] Among them, 1 is the first main reflector, 2 is the second secondary reflector, 3 is the third lens, 4 is the fourth lens, 5 is the fifth field stop, 6 is the sixth light path folding mirror, 7 is the seventh lens, 8 is the eighth lens, 9 is the ninth lens, 10 is the tenth lens, 11 is the eleventh lens, and 12 is the twelfth focusing imaging surface. DETAILED DESCRIPTION

[0045] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0046] like Figure 1 As shown, the geosynchronous orbit medium-wave infrared catadioptric passive athermal high-resolution space remote sensing camera system according to an embodiment of the present invention comprises a first primary reflector 1, a second primary reflector 2, a third lens 3, a fourth lens 4, a fifth field stop 5, a sixth optical path folding mirror 6, a seventh lens 7, an eighth lens 8, a ninth lens 9, a tenth lens 10, an eleventh lens 11, and a twelfth focusing imaging surface 12. The first primary reflector 1 and the second secondary reflector 2 together form a classic Cassegrain double-reflector system; the third lens 3, the fourth lens 4, the seventh lens 7, the eighth lens 8, the ninth lens 9, and the tenth lens 10 form a rear-mounted six-element spherical lens group; the fifth lens 5 is a field stop with a central aperture; the eleventh lens 11 is a flat glass cold stop for the detector, located at the system's exit pupil; and the twelfth focusing imaging surface 12 is where the detector is located.

[0047] The surface curvature radius of the first primary reflector is -1432.85 mm, the quadratic coefficient is -1, the reflector aperture is 600 mm in diameter, the center opening radius is 75 mm, the distance from the second secondary reflector 2 is 551.55 mm, and the material is SiC.

[0048] The surface curvature radius of the second secondary reflector 2 is -448.02mm~-447.22mm, the quadratic coefficient is -2.91~-2.89, the secondary reflector diameter is 144~146mm, the distance from the front surface of the third lens 3 is 550.28mm~551.28mm, and the material is SiC; preferably, the surface curvature radius of the second secondary reflector 2 is -447.62mm, the quadratic coefficient is -2.90, the secondary reflector diameter is 145mm, the distance from the front surface of the third lens 3 is 550.78mm, and the material is SiC.

[0049] The thickness of the third lens 3 is 18.33mm~18.37mm, the front surface curvature radius is 249.75mm~250.25mm, the rear surface curvature radius is 126mm~126.26mm, the distance from the front surface of the fourth lens 4 is 41.10mm~41.18mm, and the material is optical silicon; preferably, the thickness of the third lens 3 is 18.35mm, the front surface curvature radius is 250.00mm, the rear surface curvature radius is 126.13mm, the distance from the front surface of the fourth lens 4 is 41.14mm, and the material is optical silicon.

[0050] The thickness of the fourth lens 4 is 9.98mm~10.02mm, the front surface curvature radius is 121.99mm~122.23mm, the back surface curvature radius is 203.27mm~203.67mm, the distance from the fifth field stop 5 is 52.96mm~53.04mm, and the material is gallium arsenide; preferably, the thickness of the fourth lens 4 is 10.00mm, the front surface curvature radius is 122.11mm, the back surface curvature radius is 203.47mm, the distance from the fifth field stop 5 is 53mm, and the material is gallium arsenide.

[0051] The fifth field stop 5 is a circular ring mechanical element, the front and back surfaces are both flat, the stop thickness can be 0.8mm~1.2mm, the inner radius size of the circular ring is 11.2mm~11.4mm, the outer radius size of the circular ring is 15mm~16mm, the distance from the sixth light path folding mirror 6 is 80.00mm~80.50mm, and the material is aluminum alloy; preferably, the stop thickness is 1.00mm, the inner radius size of the circular ring is 11.3mm, the outer radius size of the circular ring is 15.5mm, the distance from the sixth light path folding mirror 6 is 80.25mm, and the material is aluminum alloy.

[0052] The sixth light path folding mirror 6 is a circular flat mirror, the flat mirror thickness can be 2.8mm~3.2mm, the diameter size is 56mm~60mm, the distance from the front surface of the seventh lens 7 is 119.95mm~120.05mm, and the material is microcrystalline glass; preferably, the flat mirror thickness can be 3mm, the diameter size is 58mm, the distance from the front surface of the seventh lens 7 is 120mm, and the material is microcrystalline glass.

[0053] The thickness of the seventh lens 7 is 5.98mm~6.02mm, the front surface curvature radius is 424.22mm~425mm, the back surface curvature radius is 285.61mm~286.21mm, the distance from the front surface of the eighth lens 8 is 24.96mm~25.04mm, and the material is optical silicon; preferably, the thickness of the seventh lens 7 is 6.00mm, the front surface curvature radius is 424.62mm, the back surface curvature radius is 285.91mm, the distance from the front surface of the eighth lens 8 is 25mm, and the material is optical silicon.

[0054] The eighth lens 8 has a thickness of 11.98 mm to 12.02 mm, a front surface curvature radius of -3130.92 mm to -3124.66 mm, a rear surface curvature radius of 582.57 mm to 583.73 mm, and a distance from the front surface of the ninth lens 9 of 3.44 mm to 3.48 mm. The material is gallium arsenide. Preferably, the eighth lens 8 has a thickness of 12.00 mm, a front surface curvature radius of -3127.79 mm, a rear surface curvature radius of 583.15 mm, a distance from the front surface of the ninth lens 9 of 3.46 mm, and a material is gallium arsenide.

[0055] The thickness of the ninth lens is 13.14mm~13.18mm, the front surface curvature radius is -48.47mm~-48.37mm, the rear surface curvature radius is -74.80mm~-74.66mm, the distance from the front surface of the ninth lens 9 is 2.98mm~3.02mm, and the material is optical silicon; preferably, the thickness of the ninth lens 9 is 13.16mm, the front surface curvature radius is -48.42mm, the rear surface curvature radius is -74.73mm, the distance from the front surface of the tenth lens 10 is 3.00mm, and the material is optical silicon.

[0056] The thickness of the tenth lens 10 is 5.58 mm to 5.54 mm, the front surface curvature radius is -75.13 mm to -75 mm, the rear surface curvature radius is -39.31 mm to -39.23 mm, the distance from the front surface of the eleventh lens 11 is 37.98 mm to 38.02 mm, and the material is optical germanium. Preferably, the thickness of the tenth lens 10 is 5.56 mm, the front surface curvature radius is -75.06 mm, the rear surface curvature radius is -39.27 mm, the distance from the front surface of the eleventh lens 11 is 38.00 mm, and the material is optical germanium.

[0057] The eleventh lens 11 is made of flat glass and serves as a cold screen. Its position coincides with the exit pupil of the camera system to achieve a 100% cold stop effect. The thickness is 4.98 mm to 5.02 mm, the distance from the imaging plane is 54.98 mm to 55.02 mm, and the material is optical germanium. Preferably, the thickness of the eleventh lens 11 is 5 mm, the distance from the imaging plane is 55 mm, and the material is optical germanium.

[0058] The twelfth surface is the focused imaging surface 12, and a medium-wave infrared detection device with a specification of 1024×1024 and a pixel size of 15 μm can be selected.

[0059] The geosynchronous orbit medium-wave infrared catadioptric passive athermal high-resolution space remote sensing camera of the embodiment of the present invention has an orbital altitude of 36,000 km, an observation band of 3 to 5 μm, an observation field of view of 0.4°×0.4°, a system focal length of 2150 mm, a relative aperture of 1:3.58, a total system length of less than 800 mm, a detector pixel size of 15 μm, a single-view swath width of 251 km×251 km, and a ground pixel resolution of 251 m. The camera is suitable for medium-wave infrared cooled detectors with a pixel size of 15 μm and a specification of 1024×1024.

[0060] The working method of a geosynchronous orbit medium-wave infrared catadioptric passive athermal high-resolution space remote sensing camera disclosed in this embodiment is as follows:

[0061] A geosynchronous orbit medium-wave infrared (MWIR) catadioptric passive athermalized high-resolution space remote sensing camera detects MWIR light from the target. The incident MWIR beam is reflected twice by a first primary reflector 1 and a second secondary reflector 2, correcting its spherical aberration. The Cassegrain double-reflector system enables the camera to have a large optical aperture, improving its sensitivity. In the rear six-element spherical lens assembly, by matching the glass refractive index, optical power, and expansion coefficient of the third, fourth, seventh, eighth, ninth, and tenth lenses 3, 4, 7, 8, 9, and 10, respectively, the thermal and chromatic aberration correction of the MWIR beam emitted from the Cassegrain double-reflector system is achieved, enhancing image quality and bringing imaging performance close to the diffraction limit. The fifth field stop 5 limits the camera's field of view and acts as a stray light filter to suppress stray light outside the field of view, improving the camera's signal-to-noise ratio. The sixth optical path folding mirror 6 deflects the imaging beam, significantly reducing the size of the remote sensing camera and conserving satellite platform space resources. Because the eleventh lens 11 is made of flat glass and acts as a cold screen, its position coincides with the camera system's exit pupil, achieving a 100% cold stop effect. This suppresses stray thermal radiation from the high-resolution space remote sensing camera itself, enabling passive athermalization of high-resolution space remote sensing imaging in geosynchronous medium-wave infrared catadioptric orbit. The twelfth focusing imaging surface 12 serves as the camera's focusing imaging plane and is where the cooled detector operates.

[0062] Figure 2 This is a distribution diagram of image plane diffuse spots in the full field of view of the geosynchronous orbit medium-wave infrared catadioptric passive athermal high-resolution space remote sensing camera system according to an embodiment of the present invention. Figure 3 This is a graph showing the variation of the root mean square radius of the diffuse spot on the image plane of a geosynchronous orbit medium-wave infrared catadioptric passive athermal high-resolution space remote sensing camera system versus the field of view. Figure 4A curve graph of a root mean square radius of an image surface diffraction spot of a geosynchronous orbit mid-wave infrared catadioptric passive athermalization high-resolution space remote sensing camera according to an embodiment of the present application varying with a field of view, Figure 5 A modulation transfer function curve of a geosynchronous orbit mid-wave infrared catadioptric passive athermalization high-resolution space remote sensing camera according to an embodiment of the present application under a 20℃ environment, Figure 6 A curve graph of an energy proportion fraction of an image surface encircled circle of a geosynchronous orbit mid-wave infrared catadioptric passive athermalization high-resolution space remote sensing camera according to an embodiment of the present application varying with a radius. Figures 2 to 6 The curve graphs of the image quality of the space remote sensing camera system according to the embodiments of the present application are close to the diffraction limit.

[0063] Figure 7 An image surface wave aberration of a geosynchronous orbit mid-wave infrared catadioptric passive athermalization high-resolution space remote sensing camera according to an embodiment of the present application under an edge field of view, Figure 8 A field curvature aberration curve and a distortion aberration curve of a geosynchronous orbit mid-wave infrared catadioptric passive athermalization high-resolution space remote sensing camera according to an embodiment of the present application, Figure 9 A curve graph of a root mean square radius of an image surface diffraction spot of a geosynchronous orbit mid-wave infrared catadioptric passive athermalization high-resolution space remote sensing camera according to an embodiment of the present application varying with a system defocus amount, Figure 10 A curve graph of an axial chromatic aberration of a geosynchronous orbit mid-wave infrared catadioptric passive athermalization high-resolution space remote sensing camera according to an embodiment of the present application, Figure 11 A curve graph of a magnification chromatic aberration of a geosynchronous orbit mid-wave infrared catadioptric passive athermalization high-resolution space remote sensing camera according to an embodiment of the present application. Figures 7 to 11 The curve graphs of the field curvature, the distortion, the defocus, the axial chromatic aberration and the magnification chromatic aberration of the space remote sensing camera system according to the embodiments of the present application are well corrected, and the wave aberration of the system is much better than the Rayleigh criterion.

[0064] Figure 12 A modulation transfer function curve of a geosynchronous orbit mid-wave infrared catadioptric passive athermalization high-resolution space remote sensing camera according to an embodiment of the present application under a -30℃ environment, Figure 13 A modulation transfer function curve of a geosynchronous orbit mid-wave infrared catadioptric passive athermalization high-resolution space remote sensing camera according to an embodiment of the present application under a 50℃ environment. Figure 12 and Figure 13 The curve graphs of the modulation transfer functions of the space remote sensing camera system according to the embodiments of the present application under the temperatures of -30℃ to 50℃ are close to the diffraction limit, and the imaging quality is good.

[0065] In summary, the geosynchronous orbit middle wave infrared catadioptric passive athermalization high-resolution space remote sensing camera of the application effectively increases the system optical aperture by adopting catadioptric structure, and reduces the volume and weight of the system. The influence of temperature change on the performance of the optical system is reduced by reasonable matching of optical materials and structural materials and reasonable distribution of lens group focal power, and the system has good imaging quality in a wide temperature range and excellent environmental adaptability. The application can be applied to the field of space remote sensing for earth observation.

[0066] The above specific description further details the purpose, technical scheme and beneficial effects of the application. It should be understood that the above description is only a specific embodiment of the application and is not used to limit the protection scope of the application. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the application should be included in the protection scope of the application.

Claims

1. A geostationary medium-wave infrared catadioptric passive athermal high-resolution remote sensing camera, characterized by: It is a geosynchronous orbit medium-wave infrared catadioptric passive athermal high-resolution space remote sensing camera, including a Cassegrain double-reflection system, a rear six-piece spherical lens group, a field aperture, an optical path folding mirror, a cold aperture, and a detector; the Cassegrain double-reflection system adopts a parabolic first main reflector and a rotating hyperbolic second secondary reflector. The incident medium-wave infrared light beam is reflected twice by the first main reflector and the second secondary reflector to achieve spherical aberration correction of the medium-wave infrared light beam. The Cassegrain double-reflection system is used to give the space remote sensing camera a large optical aperture; the rear six-piece spherical lens group is mainly composed of a third lens, a fourth lens, a seventh lens, an eighth lens, a ninth lens, and a tenth lens. The rear six-piece spherical lens group distributes the optical power of the lens to the Cassegrain double-reflection system The emitted medium-wave infrared light beam is chromatically corrected; the third lens, the seventh lens, and the ninth lens are made of optical silicon material, the fourth lens and the eighth lens are made of optical gallium arsenide material, and the tenth lens is made of optical germanium material. Passive athermal imaging is achieved by matching the refractive index and expansion coefficient of the above lenses; the field aperture is the fifth element with a central opening; the optical path is deflected by the optical path folding mirror to compress the volume of the space remote sensing camera; the cold aperture is the cold aperture of the detector, corresponding to the eleventh lens, and is a flat glass made of optical germanium material. It is located at the exit pupil position of the space remote sensing camera, and the exit pupil matches the detector cold aperture to achieve a cold aperture effect to suppress the stray heat radiation of the space remote sensing camera itself; the twelfth surface is the focused imaging surface, which is where the detector is located; The surface curvature radius of the first primary reflector is -1434.25mm to -1431.45mm; The surface curvature radius of the second secondary reflector is -448.02mm to -447.22mm; The third lens has a front surface curvature radius of 249.75mm to 250.25mm and a rear surface curvature radius of 126mm to 126.26mm. The fourth lens has a front surface curvature radius of 121.99 mm to 122.23 mm, and a rear surface curvature radius of 203.27 mm to 203.67 mm. The seventh lens has a front surface curvature radius of 424.22 mm to 425 mm, and a rear surface curvature radius of 285.61 mm to 286.21 mm. The eighth lens has a front surface curvature radius of -3130.92 mm to -3124.66 mm, and a rear surface curvature radius of 582.57 mm to 583.73 mm. The ninth lens has a front surface curvature radius of -48.47 mm to -48.37 mm, and a rear surface curvature radius of -74.80 mm to -74.66 mm. The front surface curvature radius of the tenth lens is -75.13 mm to -75 mm, and the rear surface curvature radius is -39.31 mm to -39.23 mm.

2. The geostationary orbit medium-wave infrared catadioptric passive athermal high-resolution remote sensing camera according to claim 1, characterized in that: The quadratic coefficient of the first primary reflector is -1.01 to -0.99, the outer diameter of the primary reflector is not less than 600 mm, the radius of the central opening of the primary reflector is 74 to 76 mm, the distance from the second secondary reflector is 551.50 mm to 551.60 mm, and the material is SiC; The quadratic coefficient of the second secondary reflector is -2.91 to -2.89, the diameter of the secondary reflector is 144 mm to 146 mm, the distance from the front surface of the third lens is 550.28 mm to 551.28 mm, and the material is SiC; The thickness of the third lens is 18.33 mm to 18.37 mm, and the distance from the front surface of the fourth lens is 41.10 mm to 41.18 mm; The fourth lens has a thickness of 9.98 mm to 10.02 mm and a distance from the field stop to the fourth lens from 52.96 mm to 53.04 mm. The field aperture member is a circular mechanical component that also serves as a stray light elimination aperture; the front and rear surfaces are both flat, the aperture member has a thickness of 0.8mm to 1.2mm, an inner radius of the ring is 11.2mm to 11.4mm, an outer radius of the ring is 15mm to 16mm, and the distance from the sixth optical path folding mirror is 80.00mm to 80.50mm. The material is aluminum alloy; The optical path folding mirror is a plane reflector, which is the sixth element. The plane reflector has a thickness of 2.8 mm to 3.2 mm, a diameter of 56 mm to 60 mm, and a distance from the front surface of the seventh lens of 119.95 mm to 120.05 mm. The material is microcrystalline glass. The seventh lens has a thickness of 5.98 mm to 6.02 mm and a distance from the front surface of the eighth lens to the seventh lens is 24.96 mm to 25.04 mm; The eighth lens has a thickness of 11.98 mm to 12.02 mm and a distance from the front surface of the ninth lens to the eighth lens of the ninth lens of the ninth lens of the ninth lens of the ninth lens of the ninth lens. The thickness of the ninth lens is 13.14 mm to 13.18 mm; The tenth lens has a thickness of 5.58 mm to 5.54 mm and a distance from the front surface of the eleventh lens to ... The eleventh lens is made of flat glass and serves as a cold screen. Its position coincides with the exit pupil of the camera system, its thickness is 4.98 mm to 5.02 mm, and its distance from the imaging plane is 54.98 mm to 55.02 mm.

3. The geostationary orbit medium-wave infrared catadioptric passive athermal high-resolution remote sensing camera according to claim 2, characterized in that: The surface curvature radius of the first primary reflector is -1432.85 mm, the quadratic coefficient is -1, the primary reflector aperture is 600 mm, the central opening radius is 75 mm, and the distance from the second secondary reflector is 551.55 mm; The curvature radius of the second secondary reflector is -447.62 mm, the quadratic coefficient is -2.90, the diameter of the secondary reflector is 145 mm, and the distance from the front surface of the third lens is 550.78 mm; The third lens has a thickness of 18.35 mm, a front surface curvature radius of 250.00 mm, a rear surface curvature radius of 126.13 mm, and is 41.14 mm away from the front surface of the fourth lens. The fourth lens has a thickness of 10.00 mm, a front surface curvature radius of 122.11 mm, a rear surface curvature radius of 203.47 mm, and a distance from the field stop of 53 mm. The thickness of the aperture element is 1.00 mm, the inner radius of the ring is 11.3 mm, the outer radius of the ring is 15.5 mm, and the distance from the optical path folding mirror is 80.25 mm; The plane reflector is 3 mm thick, 58 mm in diameter, 120 mm from the front surface of the seventh lens, and is made of glass-ceramic. The seventh lens has a thickness of 6.00 mm, a front surface curvature radius of 424.62 mm, a rear surface curvature radius of 285.91 mm, and is 25 mm from the front surface of the eighth lens. The eighth lens has a thickness of 12.00 mm, a front surface curvature radius of -3127.79 mm, a rear surface curvature radius of 583.15 mm, and is 3.46 mm from the front surface of the ninth lens. The ninth lens has a thickness of 13.16 mm, a front surface curvature radius of -48.42 mm, a rear surface curvature radius of -74.73 mm, and is 3.00 mm away from the front surface of the tenth lens. The tenth lens has a thickness of 5.56 mm, a front surface curvature radius of -75.06 mm, a rear surface curvature radius of -39.27 mm, and is 38.00 mm from the front surface of the eleventh lens. The eleventh lens is 5mm thick and 55mm away from the imaging plane; The twelfth surface is the focusing imaging surface, with a specification of 1024×1024 and a pixel size of 15 μ m medium-wave infrared cooled detector.

4. The geostationary orbit medium-wave infrared catadioptric passive athermal high-resolution remote sensing camera according to claim 1, characterized in that: A geosynchronous orbit medium-wave infrared (MWIR) catadioptric, passive athermal, high-resolution space remote sensing camera detects MWIR light from the target. In the six-element rear spherical lens assembly, the glass refractive index, optical power, and expansion coefficient of the third, fourth, seventh, eighth, ninth, and tenth lenses are matched to correct for thermal and chromatic aberrations of the MWIR beam emitted from the Cassegrain double-reflector system, improving imaging quality. A field stop restricts the camera's field of view and acts as a stray light diaphragm to suppress stray light outside the field of view, improving the camera's signal-to-noise ratio. An optical folding mirror deflects the imaging beam, significantly reducing the camera's size and conserving space resources on the satellite platform. Because the eleventh lens is made of flat glass and serves as a cold screen, its position coincides with the camera's exit pupil, achieving a 100% cold screen effect and enabling MWIR catadioptric, passive athermal, high-resolution space remote sensing imaging in geosynchronous orbit.

Images