A high-resolution spectral imaging device for monitoring atmospheric greenhouse gases

Abstract

The present application relates to a kind of high-resolution spectral imaging devices for monitoring atmospheric greenhouse gases, suitable for visible to infrared spectral imaging, by wide field of view small pre-system, spectral imaging instrument is composed of.Incident light is passed through after pre-system entrance slit, filter, first lens, is illuminated to off-axis concave mirror, is reflected to plane grating, and dispersed light is illuminated back off-axis concave mirror after grating, so that dispersed spectrum converges to fold mirror, after second lens, so that spectrum is further focused to detector.The present application solves the problem of small system detection width, low time resolution in prior art for monitoring atmospheric greenhouse gases.The present application has large field of view, high spatial resolution (2km), high spectral resolution (0.05nm @ 760nm), high time resolution (1 day time), compact structure, small volume, and can be applied to aerospace remote sensing field.

Description

Technical Field

[0001] This invention belongs to the field of spectral imaging, specifically relating to a high-resolution spectral imaging device for monitoring atmospheric greenhouse gases, used to detect the distribution and concentration changes of atmospheric greenhouse gas components such as CO2 and CH4. Background Technology

[0002] Since the industrial era, the levels of greenhouse gases and pollutants in the atmosphere have been rising continuously. In particular, greenhouse gases have led to global climate change, characterized by global warming, which has become a global environmental problem and poses a severe challenge to the sustainable development of the global economy. The international community has gradually reached a consensus that "greenhouse gas emission reduction is the most effective way to curb global warming."

[0003] The fundamental substance for spectral remote sensing monitoring of atmospheric greenhouse gas concentrations is gas molecules. During solar radiation absorption into the atmosphere, atmospheric molecules such as CO2 and CH4 absorb certain spectral bands, forming characteristic absorption peaks. These absorption peaks, combined with corresponding inversion algorithms, allow for the acquisition of greenhouse gas concentrations and their distribution. Spectral remote sensing technology offers advantages such as objectivity, continuity, stability, large-scale coverage, and repeatability, making it an internationally recognized method for global carbon inventory. In recent years, Europe, the United States, Japan, Canada, and China have all launched satellites capable of observing atmospheric greenhouse gas concentrations. The SCIAMACHY payload on the European environmental satellite ENVISAT, launched in 2002, is an 8-channel grating spectrometer with an orbital altitude of 800 km. Its operating wavelength range is 0.24 μm to 2.38 μm, with a spectral resolution of 0.22 nm to 1.48 nm and a spatial resolution of 30 km × 60 km. In nadir mode, its swath width is approximately 960 km, and it revisits at least once every 3 days. However, it has the following drawbacks: due to the low spectral and spatial resolution of the greenhouse gas monitoring spectral band, the accuracy of obtaining greenhouse gas concentrations is relatively low. At the same time, the temporal resolution is not high (revisiting at least once every 3 days), and it cannot fully meet the requirement of timely acquisition of global carbon flux and change information. In 2016, my country successfully launched the ACGS payload on the Carbon Dioxide Observation Satellite (TANSAT). Its optical path structure is similar to that of the US OCO-2, which is a 3-channel grating spectrometer. It has an orbit of about 700km in high orbit, an operating wavelength range of 0.758um~2.08um, a spectral resolution of 0.044nm~0.1nm, a spatial resolution of 2km×2km, a scan swath of 20km@nadir, and a revisit time of at least 16 days. However, it has the following disadvantages: small scan swath (20km) and low temporal resolution (revisit time of at least 16 days). The TANSO-FTS satellite, launched by Japan on the GOSAT-02 satellite in 2018, is a 4-channel Fourier transform interferometric spectrometer. It orbits at an altitude of 613 km, operates in the wavelength range of 0.75 μm to 14.3 μm, has a spectral resolution of 0.04 nm to 5.52 nm, a spatial resolution of 10.5 km, and a scan swath of 903 km at the nadir. It revisits at least once every 3 days. However, it has the following drawbacks: low temporal resolution (at least once every 3 days), and ground sampling points are isolated areas, making it difficult to obtain continuous spatial greenhouse gas concentration information. Interferometric spectrometers obtain greenhouse gas spectral information by reconstructing spectra from interferograms; they cannot image the detection area, meaning they cannot obtain specific spatial information, only spatial spectral information. All of these optical payloads for monitoring greenhouse gases suffer from the following drawbacks: low temporal resolution, scan swaths less than 1000 km, inability to meet global observation needs in a timely manner, and lack of the ability to acquire global carbon flux and distribution change information within a single day.Therefore, an optical system is needed that can achieve high temporal resolution and wide-area global greenhouse gas monitoring, while also ensuring high spatial and spectral resolution, and is compact and small in size.

[0004] like Figure 1 The system shown is a beam splitting system based on lens collimation and convergence (derived from the American OCO-2 spectrometer): light passes through the first slit 11 and illuminates the first collimating lens group 12. After collimation, it illuminates the planar grating 13. After dispersion by the grating, the spectral lines illuminate the first converging lens group 14. After convergence, the spectrum is finally focused onto the first detector 15. The relative aperture of the incident end of this system is 1 / 1.8, while the front telescope system adopts the Cassegrain system, and its relative aperture is also 1 / 1.8. Despite its high spectral and spatial resolution, NASA's OCO-2 satellite has a small swath (20km @ orbital altitude = 705km, meaning a small field of view) and low temporal resolution (revisiting at least once every 16 days). Furthermore, the system's size is relatively large (optical path volume is length (1037mm) × width (410mm) × height (145mm)) due to its high spectral resolution and high light throughput design. Moreover, the collimating and converging lenses require multiple aspherical single-lens plates. Since transmissive structures generally have high stray light, anti-reflection coatings (anti-reflective coatings) are needed on each lens surface to prevent specular reflection and increased stray light. Therefore, it is difficult to meet the requirements of small size, high temporal resolution, and relatively low cost for a beam splitting system based on lens collimation and converging.

[0005] like Figure 2The diagram shows a spectroscopic system structure based on an immersion grating (derived from the short-wave infrared spectrometer of the European Space Agency's Tropomi payload): Light passes through the second slit 31 and the long-pass filter 32 to illuminate the plane mirror 33, and after reflection, it illuminates the second collimating lens group 34. After collimation, it illuminates the immersion grating 35, and after dispersion, its spectrum is focused onto the second detector 37 by the second converging lens group 36. This beam splitting system is generally used in the visible and infrared bands. Although the design of a beam splitting system based on this structure is relatively small, to achieve good image quality, the relative aperture of the front telescope system needs to be matched, also using the same small relative aperture. Furthermore, the collimating lens group and converging lens group contain multiple lenses, resulting in low overall system light energy utilization. Simultaneously, the immersion grating requires a high line count and high diffraction order, similar to the characteristics of a mid-level echelle grating. Moreover, the substrate material of this immersion grating is the optical material silicon, and the grating grooves are V-shaped. Groove formation generally requires reactive ion beam etching. Silicon is relatively slow to etch using pure physical ion bombardment, often requiring chemical reactants to accelerate the etching process. Before etching, a holographic exposure is needed to create a grating mask. If the grating area is large, uneven etching can occur, resulting in high manufacturing costs and long production cycles, necessitating repeated parameter adjustments. Furthermore, this short-wave infrared spectrometer has a low spectral resolution of approximately 0.25 nm, and the overall spatial resolution, combined with the front-view telescope system, is only 7 km × 7 km. High-precision monitoring of methane greenhouse gases requires a spectral resolution better than 0.2 nm and a spatial resolution better than 7 km. In Europe and America, greenhouse gas spectrometers primarily use immersion grating designs, while my country, limited by its weak grating design and fabrication technology, has not yet achieved commercial application of such products.

[0006] Therefore, there is an urgent need for an optical imaging system that simultaneously meets the requirements of high spectral resolution (0.05nm@760nm), spatial resolution (2km×2km@nadir), temporal resolution (monitoring the entire globe in one day), large field of view (FOV≥100°), and small size (less than length (470mm)×width (420mm)×height (260mm)). Furthermore, it is required that the system is not limited by the fabrication of diffraction gratings, and that the diffraction gratings in this optical system also have the characteristics of high diffraction efficiency (over 50%). Summary of the Invention

[0007] To overcome the shortcomings of existing technologies, this invention provides a high-resolution spectral imaging device for monitoring atmospheric greenhouse gases. It features a small size, high resolution (combined with existing detector products, spectral resolution (VIS-NIR) of 0.05nm~0.15nm; spatial resolution of 2km×2km@orbital altitude=705km; temporal resolution of 1 day for global monitoring), and meets the requirement of a large field of view (FOV≥100°). Furthermore, the grating has high diffraction efficiency (absolute diffraction efficiency ≥50% across the entire wavelength band), making it suitable for aerospace and space remote sensing applications.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A high-resolution spectral imaging device for monitoring atmospheric greenhouse gases includes a small, wide-field-of-view reflective off-axis front-view telescope system and a spectral imager. The wide-field-of-view small reflective off-axis front-view telescope system includes an entrance pupil diaphragm, a first concave mirror, a first anti-stray diaphragm, a folding mirror, a second anti-stray diaphragm, a polarizer, a convex mirror, a second concave mirror, and a dichroic separator, through which incident light passes in sequence. The dichroic separator, according to the order of light incidence, has a first surface that is a standard plane and a second surface that is a high-order aspherical surface, and is used to divide the spectral imaging optical path into two spectral segment channels; each spectral segment channel corresponds to a spectral imager. The spectral imager includes an entrance slit, a filter, a first lens, an off-axis concave mirror, a plane grating, a folded plane mirror, a second lens, and a detector. Light from the two spectral band channels passes sequentially through their respective entrance slits, filters, first lenses, off-axis concave mirrors, plane gratings, folded plane mirrors, and second lenses, and is focused onto their respective detectors.

[0009] Furthermore, the planar grating is located on one side of the entrance slit, the first lens, and the off-axis concave mirror.

[0010] Furthermore, the first concave reflector is a concave spherical surface reflector; the folded reflector is a reflective Schmidt correction plate; the depolarizer is a spatial pseudo depolarizer; the convex reflector is a convex secondary aspherical surface; and the second concave reflector is a concave secondary aspherical surface. Furthermore, the entrance slit is a curved slit used to correct spatial distortion of the final imaging plane of the system; the filter is a single-pass filter used to eliminate interference light outside the operating wavelength and reduce stray light in the optical system; the first lens is an off-axis lens; the off-axis concave mirror is an off-axis aspherical mirror; the planar grating is a holographic planar grating; the second lens is an off-axis lens; and the detector is an area array detector.

[0011] Furthermore, the relative aperture of the wide-field-of-view small reflective off-axis front-view telescope system is 1 / 3 to 1 / 4, and the field of view (FOV) ranges from 100° to 120°.

[0012] Furthermore, the entrance slit, the filter, the first lens, the off-axis concave mirror, the folded plane mirror, the second lens, and the detector are located on the same side of the diffraction grating.

[0013] Furthermore, the groove shape of the diffraction grating is sinusoidal, the working diffraction order is 1, and the absolute diffraction efficiency in the working band is above 50% in the near-Littrow state.

[0014] Furthermore, the relative aperture of the spectral imager is 1 / 3 to 1 / 4.

[0015] Furthermore, the spectral imager is suitable for the following spectral bands: 0.75~0.774um, 1.6~1.622um, 2.045~2.085um, and 2.3~2.345um.

[0016] Furthermore, the incident light passes through the entrance slit and the filter to illuminate the first lens. After passing through the first lens, it illuminates the off-axis concave mirror, guiding the incident light onto the reflective plane grating. The dispersed light, after being dispersed by the plane grating, approaches the Littrow state and illuminates the off-axis concave mirror, causing the dispersed spectrum to converge and illuminate the folding mirror. After reflection, it illuminates the second lens, and after passing through, the spectrum is further focused onto the detector.

[0017] In this invention, the same central plane refers to the YOZ plane of the optical system; A small, wide-field-of-view, reflective off-axis front-view telescope system is used to receive incident light from a light source, and transmit the incident light sequentially through the entrance pupil stop, the first concave mirror, the first anti-stray light stop, the folded mirror, the second anti-stray light stop, the depolarizer, the convex mirror, the second concave mirror, the dichroic filter, and finally to the entrance slit of the spectral imager. Incident light passing through the entrance slit is filtered and then illuminates the first lens. The filter is used to eliminate interfering light outside the wavelength used and reduce stray light in the optical system. The first lens is used to deflect the light path, adjust the distance between the light rays passing through it and the planar grating, avoid interference between the two, and correct system aberrations. The incident light passes through the first lens and is transmitted to the off-axis concave mirror. The off-axis concave mirror is used to collimate the incident light and correct system aberrations, and guide the incident light onto the planar grating; The planar grating separates different wavelengths in the incident light to form a spectrum through the dispersive properties of the diffraction grating. The spectrum is transmitted back to the off-axis concave mirror in a near-Littrow state, converges the spectral lines and corrects system aberrations, and the spectrum is transmitted to the folded mirror. The folding mirror is used to fold back the optical path and reduce the volume of the optical path. The spectrum is transmitted to the second lens through the folding mirror. The second lens is used to further converge the spectral lines and correct system aberrations, and finally the spectrum is focused onto the detector; Preferably, the filter is a single-pass filter or a long-pass filter.

[0018] Preferably, the planar grating is a holographic diffraction grating according to the manufacturing process, and the groove shape of the planar grating is sinusoidal, with an absolute diffraction efficiency of more than 50% in the working band when it is close to the Littrow state.

[0019] Preferably, the detector is operatively positioned closer to the off-axis concave mirror than to the planar grating. In various embodiments, the entrance slit and the detector are on the same side of the planar grating.

[0020] Preferably, the zero-order light (i.e. reflected light) of the planar grating is emitted in a direction that deviates from the detector and the concave reflector.

[0021] Preferably, the incident light is nearly collimated and transmitted to the planar grating after passing through the off-axis concave mirror.

[0022] Preferably, the filter is optically located between the entrance slit and the first lens.

[0023] The advantages of this invention compared to the prior art are as follows: (1) The present invention has a compact structure and can be made small in size. At the same time, it can achieve high spectral resolution, high spatial resolution and high temporal resolution, and can be effectively used in aviation and aerospace remote sensing applications.

[0024] (2) The planar diffraction grating in this invention is a holographic grating with low stray light, high dispersion, high diffraction efficiency and easy fabrication.

[0025] (3) The relative aperture of the optical system of the present invention can be from 1 / 3 to 1 / 4, which is beneficial for achieving a high signal-to-noise ratio in spectrometers.

[0026] (4) In this invention, the zero-order light (i.e. reflected light) of the planar diffraction grating deviates from the detector and the off-axis concave mirror. The zero-order light is easily blocked, which effectively reduces stray light in the optical system.

[0027] (5) The optical system design format of the present invention has good versatility and can be used in different spectral ranges of ultraviolet, visible and infrared.

[0028] Compared to most previous designs, this invention makes it easier to achieve high temporal resolution and wide-swath global greenhouse gas monitoring, while ensuring high spatial and spectral resolution. It also features a compact structure, small size, high grating diffraction efficiency, low stray light optical design, and wide detection swath. This invention has the characteristics of a large field of view, high spatial resolution (2km), high spectral resolution (0.05nm@760nm), and high temporal resolution (1 day), and can be effectively used in the fields of air and space remote sensing. Attached Figure Description

[0029] Figure 1 It is a typical design diagram of a beam splitting system based on an immersion grating, according to existing technology; Figure 2 It is a typical beam splitting system design based on lens collimation and convergence according to existing technology; Figure 3 This is a schematic diagram of the high-resolution spectral imaging system for monitoring atmospheric greenhouse gases according to the present invention; Figure 4 This is a schematic diagram of the dual-channel spectral imaging device of the present invention, which has a full field of view of 120° and a dichroic filter (the system relative aperture 1 / F# = 1 / 3). Figure 5 This is a schematic diagram of a dual-channel spectral imaging device for blocking a light trap in the form of a 0th-order photophysical barrier of a diffraction grating, according to an embodiment of the present invention. Figure 6 This is a schematic diagram of a dual-channel spectral imaging device according to an embodiment of the present invention, which has a working wavelength range of 0.75–0.774 μm and 1.6–1.622 μm and a relative aperture of 1 / F# = 1 / 4. Figure 7 This is a schematic diagram of a dual-channel spectral imaging device according to an embodiment of the present invention, which has a working wavelength range of 2.045–2.085 μm and 2.3–2.345 μm and a relative aperture of 1 / F# = 1 / 3.2. Figure 8 yes Figure 6 The embodiment provides a diffraction efficiency curve for a diffraction grating with a working wavelength of 0.75–0.774 μm; Figure 9 yes Figure 6 The embodiment provides a diffraction efficiency curve for a diffraction grating with a working wavelength of 1.6–1.622 μm; Figure 10 yes Figure 7The embodiment provides a diffraction efficiency curve for a diffraction grating with a working wavelength of 2.045–2.085 μm; Figure 11 yes Figure 7 The embodiment provides a diffraction efficiency curve for a diffraction grating with a working wavelength of 2.3–2.345 μm; The attached figures are labeled as follows: First slit 11, first collimating lens group 12, planar grating 13, first converging lens group 14, first detector 15, serrated light trap 16; Second slit 31, long-pass filter 32, plane mirror 33, second collimating lens group 34, immersion grating 35, second converging lens group 36, second detector 37; 1. Entrance pupil aperture, 2. First concave mirror, 3. First anti-stray aperture, 4. Folding mirror, 5. Second anti-stray aperture, 6. Depolarizer, 7. Convex mirror, 8. Aperture stop, 9. Second concave mirror, 10. Dichroic filter. 41. Channel 1 entrance slit; 42. Channel 1 filter; 43. Channel 1 first lens; 44. Channel 1 off-axis concave mirror; 45. Channel 1 holographic plane grating; 46. Channel 1 folding plane mirror; 47. Channel 1 second lens; 48. Channel 1 detector. Channel 2 entrance slit 21, Channel 2 filter 22, Channel 2 first lens 23, Channel 2 off-axis concave mirror 24, Channel 2 holographic plane grating 25, Channel 2 folded plane mirror 26, Channel 2 second lens 27, Channel 2 detector 28, light trap 29. Detailed Implementation

[0030] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0031] exist Figures 3 to 7The illustrated embodiment demonstrates a high-resolution spectral imaging system for monitoring atmospheric greenhouse gases. The system is used for spectral imaging analysis of atmospheric greenhouse gases. The incident light sequentially passes through the entrance pupil stop 1, first concave mirror 2, first stray light removal stop 3, folded mirror 4, second stray light removal stop 5, depolarizer 6, convex mirror 7, aperture stop 8, and second concave mirror 9 in the wide-field-of-view small reflective off-axis front telescope system. After passing through the dichroic filter 10, it is split into reflected and transmitted light. The reflected light passes through the entrance slit 41, filter 42, and first lens 43, and then illuminates the off-axis concave mirror 44, guiding the incident light onto the holographic planar grating 45. After dispersion by the diffraction grating, the dispersed light approximates a Littrow shape. The light is reflected back to the off-axis concave mirror 44 of channel one, causing the dispersed spectrum to converge and illuminate the folded plane mirror 46 of channel one. After reflection, it illuminates the second lens 47 of channel one, and after passing through, the spectrum is further focused onto the detector 48 of channel one. Meanwhile, the transmitted light passes through the entrance slit 21 of channel two, the filter 22 of channel two, and the first lens 23 of channel two, and then illuminates the off-axis concave mirror 24 of channel two. The incident light is guided to the holographic plane grating 25 of channel two. After being dispersed by the diffraction grating, the dispersed light approaches the Littrow state and is reflected back to the off-axis concave mirror 24 of channel two, causing the dispersed spectrum to converge and illuminate the folded plane mirror 26 of channel two. After reflection, it illuminates the second lens 27 of channel two, and after passing through, the spectrum is further focused onto the detector 28 of channel two.

[0032] In this system, the detector 48 of channel one and the entrance slit 41 of channel one are located on the same side of the holographic plane grating 45 of channel one, and the detector 28 of channel two and the entrance slit 21 of channel two are located on the same side of the holographic plane grating 25 of channel two. This beam-splitting structure significantly reduces the volume of the system's optical path structure, while easily achieving high spectral resolution, high light flux, and low stray light. Furthermore, the holographic diffraction grating with sinusoidal grooves in this beam-splitting system also exhibits high diffraction efficiency (≥50%), and these designs are superior to those of other systems. Figure 1 The design of the beam splitting system based on lens collimation and convergence has significant advantages.

[0033] like Figure 2As shown, the beam splitting system based on an immersion grating includes a second collimating lens group 34 and a second converging lens group 36. Although the beam splitting system designed based on this structure has a relatively small volume, to achieve good image quality, the incident end of the beam splitting system can only use a small relative aperture (1 / 8 to 1 / 10). Furthermore, the second collimating lens group 34 and the second converging lens group 36 use multiple lenses, resulting in low overall system light energy utilization. Additionally, the immersion grating 35 requires a high scribe line count, and the substrate material of the immersion grating 35 is optical material silicon, with V-shaped grooves, making the grating fabrication process relatively complex. This invention… Figure 3 The illustrated embodiment provides a schematic diagram of the structure of a spectral imaging device for atmospheric greenhouse gas spectral analysis, including an entrance pupil aperture 1, a first concave mirror 2, a first stray light removal aperture 3, a folded mirror 4, a second stray light removal aperture 5, a polarizer 6, a convex mirror 7, an aperture diaphragm 8, a second concave mirror 9, a dichroic filter 10, a channel-1 entrance slit 41, a channel-1 filter 42, a channel-1 first lens 43, a channel-1 off-axis concave mirror 44, a channel-1 holographic plane grating 45, a channel-1 folded plane mirror 46, a channel-1 second lens 47, and a channel-1 detector 48; a channel-2 entrance slit 21, a channel-2 filter 22, a channel-2 first lens 23, a channel-2 off-axis concave mirror 24, a channel-2 holographic plane grating 25, a channel-2 folded plane mirror 26, a channel-2 second lens 27, and a channel-2 detector 28, with the YOZ plane being the central plane of the optical system. In this system, the detector 48 of channel one and the entrance slit 41 of channel one are located on the same side of the holographic plane grating 45 of channel one, and the detector 28 of channel two and the entrance slit 21 of channel two are located on the same side of the holographic plane grating 25 of channel two. The dispersed light of the holographic plane grating 45 of channel one in the channel one reflective spectral imager is transmitted back to the off-axis concave mirror 44 of channel one in the YOZ plane in a near-Littrow state and finally converges to the detector 48 of channel one. The diffracted light of the holographic plane grating 25 of channel two in the channel two reflective spectral imager is transmitted back to the off-axis concave mirror 24 of channel one in the YOZ plane in a near-Littrow state and finally converges to the detector 28 of channel two.

[0034] In the beam splitting system, the off-axis concave mirror 44 of channel one and the off-axis concave mirror 24 of channel two are preferably non-spherical surfaces, which facilitates the achievement of high-quality images. The grating stripe pattern of the holographic planar grating 45 of channel one and the holographic planar grating 25 of channel two is preferably a sinusoidal, equally spaced linear groove holographic grating, which is easy to fabricate; a blazed type is also an option. The detectors 48 of channel one and 28 of channel two are area arrays, which can be selected from Teledyne e2v's HAWAII H2RG, CCD42-40, CCD55-30, or Princeton Infrared Technologies' 1280SCICAM.

[0035] In a beam splitting system, to maximize the beam energy using the first-order dispersed light and reduce the influence of stray light, this is achieved by approaching the Littrow state. The stray light depends not only on the surface quality of each optical element and the quality of the electronic components, but also on the structure of the optical system. For example, when the beam splitting system uses the first-order diffraction order of a grating, the grating incident angle α, the wavelength λ, and the number of grating lines f satisfy formula (1): |1-λf|<sin(a)<2λf-1 (1) At this point, only the first-order diffraction order and the zero-order light exist; other diffraction orders are absent, which helps reduce stray light from the optical system. Simultaneously, selecting an appropriate groove depth allows the first-order dispersion spectrum to have high diffraction efficiency, especially when 0.7 < λf < 1.2, where the average diffraction efficiency for both polarizations can reach over 50%, thus improving the signal-to-noise ratio of the spectrometer.

[0036] like Figure 4The illustration shows an embodiment of the present invention, which is a dual-channel spectral imaging device with a field of view (FOV) of 120° and a dichroic filter, which can be used for monitoring atmospheric greenhouse gas analysis. The dichroic filter 10 divides the system's operating wavelength into two visible light bands: 540nm to 570nm and 750nm to 774nm. The system's relative aperture 1 / F# = 1 / 3, where F# represents the ratio of the system's equivalent focal length to the entrance pupil diameter (f / D), and its reciprocal is also called the relative aperture. The smaller the F-number, the stronger the optical system's light-gathering ability. Both the first-channel entrance slit 41 and the second-channel entrance slit 21 are curved slits with a height of 26mm and a width of 50µm. Both the first-channel detector 48 and the second-channel detector 28 are Teledyne e2v CCD55-30s (pixel size 22.5µm × 22.5µm). In this system, the entrance slit 41 of channel one, the filter 42 of channel one, the folded plane mirror 46 of channel one, the second lens 47 of channel one, and the detector 48 of channel one are all located on the same side below the holographic plane grating 45 of channel one; the entrance slit 21 of channel two, the long-pass filter 22 of channel two, the folded plane mirror 26 of channel two, the second lens 27 of channel two, and the detector 28 of channel two are all located on the same side below the holographic plane grating 25 of channel two, making the optical system structure more compact. Its optical path volume (length × width × height) is 465 × 418 × 264 mm. The spectral length of this beam splitting system is 25.0 mm, and the spectral resolution is 0.05 nm @ 760 nm.

[0037] like Figure 5 As shown, stray light can be eliminated by setting up light traps 29. For example, in the system, incident light is collimated by the off-axis concave mirror 44 of channel one and then illuminates the holographic plane grating 45 of channel one, and after being collimated by the off-axis concave mirror 24 of channel two, it illuminates the holographic plane grating 25 of channel one. After diffraction by the gratings, zeroth-order light and first-order dispersive spectra exist, as is known to those skilled in the art. The zeroth-order light is unwanted by the system; if it is not blocked, it will become stray light. The serrated light trap minimizes light scattering. Figure 5 Multiple serrated light traps 16 (shown by thick black lines) can be set around the light propagation path to eliminate zero-order light and other stray light.

[0038] like Figure 6As shown in the figure, an embodiment of a high-resolution spectral imaging device with a field of view (FOV) of 100° and a relative aperture of 1 / F# = 1 / 4 is used for monitoring atmospheric greenhouse gas analysis. The system operates in the visible light band of 750nm to 774nm and the near-infrared band of 1600nm to 1622nm. Both the first entrance slit 41 and the second entrance slit 21 are curved slits with a height of 21mm and a width of 35um. The detector 48 of the first channel is a CCD42-40 from Teledyne e2v (pixel size 13.5um × 13.5um), and the detector 28 of the second channel is a 1280SCICAM from Princeton Infrared Technologies (pixel size 12um × 12um). In this system, Channel 1 (slit 04), Channel 1 long-pass filter 42, Channel 1 folded plane mirror 46, Channel 1 second lens 47, and Channel 1 detector 48 are all located on the same side below Channel 1 holographic plane grating 45; Channel 2 (incident slit 21), Channel 2 long-pass filter 22, Channel 2 folded plane mirror 26, Channel 2 second lens 27, and Channel 2 detector 28 are all located on the same side below Channel 2 holographic plane grating 25, making the optical system structure more compact. Its optical path volume (length × width × height) is 468 × 382 × 226 mm. The relevant parameters of this optical system are shown in Tables 1 and 2.

[0039] like Figure 7 As shown in the figure, an embodiment of a high-resolution spectral imaging device with a field of view (FOV) of 110° and a relative aperture of 1 / F# = 1 / 3.2 is used for monitoring atmospheric greenhouse gas analysis. The system operates in the short infrared bands of 2045nm to 2085nm and 2300nm to 2345nm. Both the first slit 11 and the second slit 21 are curved slits with a height of 25mm and a width of 35um. The detectors 48 of the first slit and 28 of the second slit are both HAWALL 2RG from Teledynee2v (with a pixel size of 18um × 18um). In this system, the entrance slit 41 of channel one, the filter 42 of channel one, the folded plane mirror 46 of channel one, the second lens 47 of channel one, and the detector 48 of channel one are all located on the same side below the holographic plane grating 45 of channel one; the slit 21 of channel two, the long-pass filter 22 of channel two, the folded plane mirror 26 of channel two, the second lens 27 of channel two, and the detector 28 of channel two are all located on the same side below the holographic plane grating 25 of channel two, making the optical system structure more compact. Its optical path volume (length × width × height) is 468 × 415 × 258 mm. The spectral length of this beam splitting system is 14.0 mm, and the spectral resolution is 0.1 nm @ 2062 nm.

[0040] like Figure 8 As shown, it demonstrates Figure 6 The absolute diffraction efficiency diagram of the channel-holographic planar grating in the beam-splitting system of the embodiment is shown. The holographic planar grating has 2224 lines / mm, a sinusoidal groove shape, an incident angle of 53.29°, and uses a diffraction order of -1. From... Figure 8 It can be seen that within the operating wavelength range of 750nm to 774nm, the absolute diffraction efficiency of the grating is above 51%, which is beneficial to improving the signal-to-noise ratio of high-resolution spectral imaging systems used for monitoring atmospheric greenhouse gases.

[0041] like Figure 9 As shown, it demonstrates Figure 6 The absolute diffraction efficiency diagram of the channel two holographic planar grating in the beam splitting system of the embodiment is shown. The holographic planar grating has 1058 lines / mm, a sinusoidal groove shape, an incident angle of -54.37°, and uses a diffraction order of -1. From... Figure 9 It can be seen that within the operating wavelength range of 1600nm to 1622nm, the absolute diffraction efficiency of the grating is above 52%, which is beneficial to improving the signal-to-noise ratio of high-resolution spectral imaging systems used for monitoring atmospheric greenhouse gases.

[0042] like Figure 10 As shown, it demonstrates Figure 7 The absolute diffraction efficiency diagram of the channel-holographic planar grating in the beam-splitting system of the embodiment is shown. The holographic planar grating has 816 lines / mm, a sinusoidal groove shape, an incident angle of 53.65°, and uses a diffraction order of -1. From... Figure 10 It can be seen that within the operating wavelength range of 2045nm to 2085nm, the absolute diffraction efficiency of the grating is above 52%, which is beneficial to improving the signal-to-noise ratio of high-resolution spectral imaging systems used for monitoring atmospheric greenhouse gases.

[0043] like Figure 11 As shown, it demonstrates Figure 7 The absolute diffraction efficiency diagram of the channel two holographic planar grating in the beam splitting system of the embodiment is shown. The holographic planar grating has 746 lines / mm, a sinusoidal groove shape, an incident angle of -54.60°, and uses a diffraction order of -1. From... Figure 11 It can be seen that within the operating wavelength range of 2300nm to 2345nm, the absolute diffraction efficiency of the grating is above 50%, which is beneficial to improving the signal-to-noise ratio of high-resolution spectral imaging systems used for monitoring atmospheric greenhouse gases.

[0044] Examples of analytical systems for monitoring atmospheric greenhouse gases are provided in Table 1 and Table 2 below (e.g.) Figure 6 The optical specifications and other optical parameters are provided, and descriptions of typical systems known to those skilled in the art are given.

[0045] Table 1. Example Optical Specifications (Channel 1)

[0046] Table 2 Other optical parameters used in the embodiment of the atmospheric greenhouse gas analysis system

[0047] In each embodiment, the improved optical design features an entrance slit, long-pass filter, first lens, second lens, off-axis concave mirror, and detector all located on the same side below the holographic plane grating. This design results in a more compact optical path structure with significantly less space occupied, which is beneficial for the spatial arrangement and weight reduction of the spectral imaging instrument. Furthermore, the sinusoidal slot holographic plane grating in each embodiment achieves an absolute diffraction efficiency of over 50%, which is beneficial for the signal-to-noise ratio of the spectral imaging instrument.

[0048] The above embodiments are provided merely for the purpose of describing the present invention and are not intended to limit the scope of the invention. The scope of the invention is defined by the appended claims. Various equivalent substitutions and modifications made without departing from the spirit and principles of the invention should be covered within the scope of the invention.

Claims

1. A high-resolution spectral imaging device for monitoring atmospheric greenhouse gases, characterized in that, Including a small, wide-field-of-view reflective off-axis front-view telescope system and a spectral imager; The wide-field-of-view small reflective off-axis front-view telescope system includes an entrance pupil diaphragm, a first concave mirror, a first anti-stray diaphragm, a folding mirror, a second anti-stray diaphragm, a polarizer, a convex mirror, a second concave mirror, and a dichroic separator, through which incident light passes in sequence. The dichroic separator, according to the order of light incidence, has a first surface that is a standard plane and a second surface that is a high-order aspherical surface, and is used to divide the spectral imaging optical path into two spectral segment channels; each spectral segment channel corresponds to a spectral imager. The spectral imager includes an entrance slit, a filter, a first lens, an off-axis concave mirror, a plane grating, a folded plane mirror, a second lens, and a detector. Light from the two spectral band channels passes sequentially through their respective entrance slits, filters, first lenses, off-axis concave mirrors, plane gratings, folded plane mirrors, and second lenses, and is focused onto their respective detectors. The incident light passes through the entrance slit and the filter to illuminate the first lens. After passing through the first lens, it illuminates the off-axis concave mirror, which guides the incident light to the reflective plane grating. The dispersed light is dispersed by the plane grating, and its dispersed light approaches the Littrow state and illuminates the off-axis concave mirror, causing the dispersed spectrum to converge and illuminate the folding mirror. After reflection, it illuminates the second lens, and after passing through, the spectrum is further focused onto the detector. The spectral resolution is 0.05nm~0.15nm; the spatial resolution is 2kmx2km@orbital altitude=705km; the temporal resolution is 1 day for global monitoring, and the field of view (FOV) is ≥100°.

2. The high-resolution spectral imaging device for monitoring atmospheric greenhouse gases according to claim 1, characterized in that, The first concave reflector is a concave spherical surface reflector; the folded reflector is a reflective Schmidt correction plate; the depolarizer is a spatial pseudo depolarizer; the convex reflector is a convex secondary aspherical surface; and the second concave reflector is a concave secondary aspherical surface.

3. The high-resolution spectral imaging device for monitoring atmospheric greenhouse gases according to claim 1, characterized in that, The entrance slit is a curved slit used to correct spatial distortion of the final imaging plane of the system; the filter is a single-pass filter used to eliminate interference light outside the operating wavelength and reduce stray light in the optical system; the first lens is an off-axis lens; the off-axis concave mirror is an off-axis aspherical mirror; the planar grating is a holographic planar grating; the second lens is an off-axis lens; and the detector is an area array detector.

4. A high-resolution spectral imaging device for monitoring atmospheric greenhouse gases according to claim 1, characterized in that: The relative aperture of the wide-field-of-view small reflective off-axis front-view telescope system is 1 / 3 to 1 / 4, and the field of view (FOV) ranges from 100° to 120°.

5. A high-resolution spectral imaging device for monitoring atmospheric greenhouse gases according to claim 1, characterized in that: The entrance slit, the filter, the first lens, the off-axis concave mirror, the folded plane mirror, the second lens, and the detector are located on the same side of the planar grating.

6. A high-resolution spectral imaging device for monitoring atmospheric greenhouse gases according to claim 5, characterized in that: The planar grating has sinusoidal grooves and operates at the first diffraction order. In near-Littrow mode, its absolute diffraction efficiency in the operating band is above 50%.

7. A high-resolution spectral imaging device for monitoring atmospheric greenhouse gases according to claim 1, characterized in that: The relative aperture of the spectral imager is 1 / 3 to 1 / 4.

8. A high-resolution spectral imaging device for monitoring atmospheric greenhouse gases according to claim 1, characterized in that: The spectral imager is suitable for the following spectral bands: 0.75~0.774um, 1.6~1.622um, 2.045~2.085um, and 2.3~2.345um.

9. A high-resolution spectral imaging device for monitoring atmospheric greenhouse gases according to claim 1, characterized in that: The planar grating is located on the side of the entrance slit, the first lens, and the off-axis concave mirror.

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