Infrared hyperspectral imaging system for tropospheric three-dimensional wind field detection

Abstract

The application discloses an infrared hyperspectral imaging system for troposphere three-dimensional wind field detection, and belongs to the field of space optical remote sensing, and comprises a scanning mirror, a telescope group, a slit, a collimating mirror group, a light splitting module, an imaging mirror group and a mid-wave infrared image plane. Target radiation is imaged on the slit by the telescope group after the scanning mirror, is collimated by the collimating mirror group, is spectrally separated by the light splitting module, and is imaged on the focal plane by the imaging module. The system has the advantages of compact structure, high sensitivity, high spectral resolution, small background radiation and the like. The system can provide a more economical and effective detection means for global troposphere wind field inversion.

Description

Technical Field

[0001] This invention belongs to the field of space optical remote sensing, and particularly relates to an infrared hyperspectral imaging system for detecting three-dimensional wind fields in the troposphere. Background Technology

[0002] As the core carrier of atmospheric motion, wind fields play a dominant and regulatory role in atmospheric mass transport, momentum exchange, energy transfer, and component migration. Due to their good coverage, global-scale wind field detection mainly relies on satellite payloads: active detection payloads such as lidar can achieve fine vertical wind field detection, but due to the limitations of active detection, their swath width is extremely limited, making high-frequency global coverage updates difficult; microwave scatterometers can invert ocean surface wind fields by measuring ocean surface scattering, but they are difficult to detect mid-to-upper-level atmospheric wind fields; passive payloads such as multispectral imagers rely on cloud movement to invert atmospheric wind vectors, but are limited by cloud height and instrument spectral bandwidth, resulting in a limited number of wind field inversion layers and large altitude positioning errors; infrared hyperspectral wind field detection technology, relying on the time-scale changes of observed tracers and its fine detection spectral bands, can achieve vertical multi-layer wind field inversion with high vertical positioning accuracy, possessing all-weather, clear-sky observation capabilities. Based on the interferometric atmospheric vertical sounder carried by my country's Fengyun-4 satellite, numerous scholars have fully demonstrated the application prospects of hyperspectral payloads in the field of atmospheric vertical wind field inversion. Geostationary orbit hyperspectral wind field detection technology features high temporal resolution, enabling minute-level data updates. However, geostationary orbit suffers from low spatial resolution, limited global coverage, and high cost. Furthermore, infrared hyperspectral technology, due to its narrow bandwidth, results in weak energy reception, making high sensitivity difficult to achieve, especially for geostationary orbit payloads, where it is challenging to balance high spatial resolution and high sensitivity.

[0003] Based on satellite formation technology, temporal changes in tracers can be monitored in polar orbits. Therefore, developing polar-orbiting tropospheric three-dimensional wind field detection can achieve global wind field detection with higher spatial resolution, complementing the advantages of geostationary satellites. Currently, however, existing polar-orbiting hyperspectral payloads have a spatial resolution on the order of 10 km, which is insufficient for small- to medium-scale wind field detection. Furthermore, due to their wide spectral range design, their current size and power consumption remain relatively large. On the other hand, there are currently no infrared hyperspectral payloads flying in formation, meaning that current hyperspectral-based wind field inversion data are mostly concentrated in high-latitude regions, leaving significant gaps in mid- and low-latitude data.

[0004] At present, there is no infrared hyperspectral imaging system suitable for satellite formation flight that meets the requirements for global wind field detection, with high spectral resolution, high spatial resolution, wide swath, high sensitivity, and compact size. Summary of the Invention

[0005] To address the aforementioned problems, this invention proposes an infrared hyperspectral imaging system for three-dimensional tropospheric wind field detection, maintaining high sensitivity while achieving high spatial resolution. It features a compact structure, a large number of spectral channels, and high detection sensitivity. The specific technical solution is as follows:

[0006] An infrared hyperspectral imaging system for detecting three-dimensional wind fields in the troposphere includes a scanning mirror, a telescope group, a slit, a collimating mirror group, a beam splitting module, an imaging mirror group, and a focal plane. Target radiation is reflected by the scanning mirror and enters the telescope group, which images it onto the slit. After passing through the slit, the radiation is collimated by the collimating mirror group, then split by the beam splitting module and reflected before entering the imaging mirror group, finally converging onto a detector at the focal plane.

[0007] The present invention has the following beneficial effects:

[0008] 1. This invention achieves a ground swath coverage of over 1000 km and a spatial resolution of 3 km at an orbital altitude of 500 km. Through overall optical design and the use of planar gratings, it can acquire over 560 hyperspectral image data points within the mid-infrared range of 4.08-5.72 μm, achieving a hyperspectral resolution better than 3 nm. This meets the requirements for multi-vertical stratification, small-scale detection, and rapid updating of tropospheric wind fields.

[0009] 2. This invention has a compact size and lightweight structure. It adopts a prism combined with a planar grating for beam splitting, which is simple to manufacture. While meeting the beam splitting requirements, it also reduces the size by folding the optical path. It has high applicability to satellite platforms and meets the requirements for small satellites.

[0010] 3. The system of this invention adopts a small F-number design with an F-number of 2, and simultaneously employs a low-temperature integrated cooling scheme and a cold aperture matching design, which has good anti-stray light capability and high-sensitivity weak signal detection capability, meeting the detection requirements of low-temperature weak targets for wind field inversion. Attached Figure Description

[0011] Figure 1 This is an optical path diagram of the infrared hyperspectral imaging system for tropospheric three-dimensional wind field detection according to the present invention;

[0012] Figure 2 This is a schematic diagram of the scanning field of view;

[0013] Figure 3 The MTF curve is shown at a wavelength of 4.08 μm.

[0014] Figure 4 The MTF curve is shown at a wavelength of 5 μm.

[0015] Figure 5 The MTF curve is shown at a wavelength of 5.72 μm. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this invention clearer, the 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 merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other. To achieve the above objectives, this invention adopts the following technical solution.

[0017] Reference Figure 1 This is an optical path diagram of an infrared hyperspectral imaging system for detecting three-dimensional wind fields in the troposphere. It consists of a scanning mirror 1, a telescope group P1, a slit 4, a collimating mirror group P2, a beam splitting module P3, an imaging mirror group P4, and a focal plane 15. Target radiation is reflected by the scanning mirror 1 and enters the telescope group P1, which images it onto the slit 4. After passing through the slit 4, it is collimated by the collimating mirror group P2, then split by the beam splitting module P3 and reflected before entering the imaging mirror group P4, finally converging onto the detector at the focal plane.

[0018] Scanning mirror 1 uses a single-sided plane mirror for scanning. With each scan, in addition to observations of the Earth region, it can also observe blackbodies and cold space on the satellite to achieve on-board calibration and ensure data accuracy. Telescope group P1 and collimating mirror group P2 both use Ge and Si aspherical lenses. Prism 7 reduces spectral line bending and spectral distortion caused by the plane grating and also bends the entire optical path, keeping the angle between telescope group P1, collimating mirror group P2 and imaging mirror group P3 within a small range, thus keeping the system structure compact. Imaging mirror group P3 adopts a secondary imaging design to ensure that the exit pupil matches the cold aperture, which can greatly reduce the thermal background stray light of the system and improve the detection sensitivity.

[0019] Telescope group P1 has a focal length of 50mm~60mm and includes lens 1 (2) and lens 2 (3). Lens 1 (2) and lens 2 (3) are both meniscus lenses and are both positive lenses. The convex surfaces of lens 1 (2) and lens 2 (3) are both aspherical. Lens 1 (2) and lens 2 (3) are both meniscus lenses. The concave surfaces of both lenses face the slit. The aspherical surfaces are all located on the convex surfaces. The front and rear surfaces are coated with anti-reflection coatings. The transmittance is greater than 0.95 in the wavelength range of 4μm~6μm.

[0020] The collimating lens group P2 has a focal length of 50mm~60mm and includes a third lens 5 and a fourth lens 6. Both the third lens 5 and the fourth lens 6 are meniscus lenses and are positive lenses. The convex surfaces of the third lens 5 and the fourth lens 6 are aspherical. Both the third lens 5 and the fourth lens 6 are meniscus lenses, with the concave surfaces facing the slit. The aspherical surfaces are all located on the convex surfaces. The front and rear surfaces are coated with anti-reflection coatings, and the transmittance is greater than 0.95 in the wavelength range of 4μm~6μm.

[0021] The beam-splitting module P3 includes a prism 7 and a planar grating 8. The surface of prism 7 closest to the collimating lens is perpendicular to the collimating lens's optical axis, while the other surface forms a 73° angle with the optical axis. Prism 7 is made of ZnSe material, and all its surfaces are planar. The rear surface of the prism deflects the light downwards by approximately 50° to reduce the angle between the collimating lens group and the imaging lens group, compressing the longitudinal space. The light then enters the planar grating 8, further separating the wavelengths. The planar grating 8 is a reflective blazed grating with a line density of 120 lp / mm and a diffraction order of +1. Furthermore, utilizing the difference in dispersion characteristics between the prism and the planar grating, the combination of prism 7 and planar grating 8 reduces spectral line bending and color distortion within a single pixel.

[0022] The imaging lens group P4 has a focal length of 80mm~90mm and includes lens 9 (5th), lens 10 (6th), lens 11 (7th), lens 12 (8th), and lens 13 (9th). All lenses are meniscus lenses, with lenses 9 (5th), 12 (8th), and 13 (9th) being positive lenses, and lenses 10 (6th) and 11 (7th) being negative lenses. The convex surfaces of lenses 9 (5th) and 13 (9th) are aspherical. The imaging lens group also features an exit pupil 14, achieving 100% matching of the cold aperture, which significantly reduces the impact of background radiation on the system's detection sensitivity. All lenses are meniscus lenses, with the convex surfaces of lenses 5 and 9th being aspherical. All lenses have anti-reflection coatings on both the front and back surfaces, achieving a transmittance greater than 0.95 in the wavelength range of 4μm~6μm.

[0023] To further ensure the system's detection sensitivity, the telescope assembly P1, collimating lens assembly P2, beam splitter module P3, and imaging lens assembly P4 all operate at a low temperature of 220K. The operating temperature from the exit pupil 14 to the focal plane 15 is 70K.

[0024] The target radiation signal enters the telescope group via scanning mirror 1 and is imaged at slit 4 by lenses 1 (2) and 2 (3). After being collimated by lenses 3 (5) and 4 (6) in the collimating mirror group, the light is deflected by prism 7, dispersed and reflected by plane grating 8, and then enters the imaging mirror group, where it is imaged at focal plane 15 by lenses 5 (9), 6 (10), 7 (11), 8 (12), and 9 (13). By combining prism 7 with plane grating 8, the curvature of the system's spectral lines can be reduced, and the volume can be compressed by deflecting the light.

[0025] The system has an imaging spectral range of 4.08μm to 5.72μm, an F number of 2, a spectral resolution of 3nm, and is compatible with detectors with a 640×512 pixel size of 30μm.

[0026] The slit 4 is 11 mm long and 30 μm wide.

[0027] The lenses of the telescope group P1 and the collimating lens group P2 are both made of a combination of Ge and Si materials, while the lens of the imaging lens group P3 is made of a combination of Si and ZnS materials.

[0028] The system employs a combination of pixel merging and multi-element scanning to increase the entrance pupil size and extend the integration time, thereby ensuring detection sensitivity.

[0029] The system's field of view along the orbital dimension is 11°, and the scanning mirror rotates via a motor across the orbital dimension, achieving 360° scanning. As scanning mirror 1 rotates, it sequentially scans the right edge field of view A2, the nadir point A1, the left edge field of view A3, the cold space A4, and the supersonic blackbody A5, as shown below. Figure 2 As shown.

[0030] The modulation transfer functions of the overall optical system at 4.08μm, 5μm, and 5.72μm are as follows: Figures 3-5 As shown, the diffraction is close to the limit at all wavelengths and fields of view.

[0031] Table 1 Optical parameters of each module

[0032]

[0033] like Figures 3-5 The figures show the modulation transfer function curves of all fields of view of the system at wavelengths of 4.08μm, 5μm, and 5.72μm on the image plane. It can be seen that the modulation transfer function of each wavelength in all fields of view is greater than 0.6 at the cutoff frequency of 17lp / mm, which is close to the diffraction limit, indicating that the system has good imaging quality.

Claims

1. An infrared hyperspectral imaging system for tropospheric three-dimensional wind field sounding, characterized in that, It includes a scanning mirror, a telescope group, a slit, a collimating mirror group, a beam splitter module, an imaging mirror group, and a focal plane. The target radiation is reflected by the scanning mirror and enters the telescope group. The telescope group images it onto the slit. After passing through the slit, it is collimated by the collimating mirror group, then split by the beam splitter module and reflected before entering the imaging mirror group. Finally, it converges onto the detector at the focal plane. The scanning mirror uses a single-sided plane mirror for scanning. Each scan circle, in addition to observations of the Earth region, also observes the blackbody and cold space on the satellite to achieve on-board calibration.

2. The infrared hyperspectral imaging system for tropospheric three-dimensional wind field sounding according to claim 1, characterized in that, Both the telescope and collimating lens groups use Ge and Si aspherical lenses; the imaging lens group uses a combination of Si and ZnS lenses.

3. The infrared hyperspectral imaging system for detecting three-dimensional tropospheric wind fields according to claim 1, characterized in that, The telescope assembly includes a first lens and a second lens. Both the first and second lenses are meniscus lenses with concave surfaces facing the slit and aspherical surfaces positioned on the convex surfaces. Anti-reflective coatings are applied to both the front and rear surfaces, resulting in a transmittance greater than 0.95 in the wavelength range of 4μm to 6μm.

4. An infrared hyperspectral imaging system for detecting three-dimensional wind fields in the troposphere according to claim 3, characterized in that, The collimating lens group includes a third lens and a fourth lens. Both the third and fourth lenses are meniscus lenses with their concave surfaces facing the slit and their aspherical surfaces positioned on the convex surfaces. The front and rear surfaces are coated with anti-reflective coatings, and the transmittance is greater than 0.95 in the wavelength range of 4μm to 6μm.

5. An infrared hyperspectral imaging system for detecting three-dimensional tropospheric wind fields according to claim 4, characterized in that, The beam splitter module includes a prism and a planar grating. The surface of the prism near the collimator is perpendicular to the optical axis of the collimator, and the other surface has an angle of 73° with the optical axis. The front and back surfaces are coated with anti-reflection films, and the transmittance is greater than 0.95 in the wavelength range of 4μm to 6μm. The planar grating is a reflective blazed grating, and the diffraction efficiency is better than 0.7 in the working band.

6. An infrared hyperspectral imaging system for detecting three-dimensional wind fields in the troposphere according to claim 5, characterized in that, The imaging lens group includes lens 5, lens 6, lens 7, lens 8, and lens 9. All lenses are meniscus lenses. The convex surfaces of lens 5 and lens 9 are aspherical. All lenses are coated with anti-reflective coatings on the front and back surfaces, and the transmittance is greater than 0.95 in the wavelength range of 4μm to 6μm.

7. An infrared hyperspectral imaging system for detecting three-dimensional tropospheric wind fields according to claim 6, characterized in that, The target radiation signal enters the telescope group through the scanning mirror and is imaged at the slit by the first and second lenses. After being collimated by the third and fourth lenses in the collimating lens group, the light is deflected by the prism and then dispersed and reflected by the plane grating before entering the imaging lens group, where it is imaged at the focal plane by the fifth, sixth, seventh, eighth, and ninth lenses.

8. An infrared hyperspectral imaging system for detecting three-dimensional tropospheric wind fields according to claim 1, characterized in that, The imaging spectral range is 4.08μm~5.72μm, the F number is 2, the spectral resolution is 3nm, and it is compatible with detectors with a pixel size of 30μm and a scale of 640×512.

9. An infrared hyperspectral imaging system for detecting three-dimensional wind fields in the troposphere according to claim 6, characterized in that, The convex surfaces of the 1st, 2nd, 3rd, 4th, 5th, and 9th lenses are all even-order aspherical surfaces.

10. An infrared hyperspectral imaging system for detecting three-dimensional tropospheric wind fields according to claim 1, characterized in that, The slit is 11 mm long and 30 μm wide.

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