High-resolution spectral imaging device for monitoring atmospheric greenhouse gas

Abstract

The invention relates to a high-resolution spectral imaging device for monitoring atmospheric greenhouse gas, which is suitable for visible to infrared spectral imaging and consists of a wide-view-field small front-end system and a spectral imager. Incident light passes through the entrance slit, the optical filter and the first lens after passing through the front-end system, irradiates the off-axis concave reflector and is reflected to the plane grating, and the light dispersed after passing through the grating is close to a Littrow state and irradiates back to the off-axis concave reflector, so that a dispersed spectrum is converged to irradiate the mirror and passes through the second lens, and the spectrum is further focused to the detector. According to the invention, the problems of small detection breadth and low time resolution of an atmospheric greenhouse gas monitoring system in the prior art are solved. The invention has the advantages of large field of view, high spatial resolution (2km), high spectral resolution (0.05 nm-760nm), high time resolution (one day), compact structure and small volume, and can be applied to the field of aerospace remote sensing.

Description

Technical Field

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

[0002] Since the industrial age, the content of greenhouse gases and pollutants in the atmosphere has continued to increase. In particular, global climate change characterized by global warming caused by greenhouse gases has become a global environmental problem, posing severe challenges 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 basic substance of spectral remote sensing monitoring of atmospheric greenhouse gas content is gas molecules. When sunlight radiates into the atmosphere, atmospheric molecules such as CO2 and CH4 absorb certain spectral bands. This absorption forms different characteristic absorption peak spectral lines, which are then used with corresponding inversion algorithms to obtain the concentration of greenhouse gases and their distribution changes. Spectral remote sensing technology has the advantages of being objective, continuous, stable, large-scale, and repeated, and has become an internationally recognized global carbon inventory method. In recent years, Europe, the United States, Japan, Canada, and China have all launched satellites capable of observing atmospheric greenhouse concentrations. The SCIAMACHY payload on the European environmental satellite ENVISAT launched in 2002 is an 8-channel grating spectrometer with an orbit altitude of 800km, an operating wavelength range of 0.24um~2.38um, a spectral resolution of 0.22nm~1.48nm, a spatial resolution of 30km×60km, a swath of about 960km in nadir mode, and a revisit period of at least 3 days. However, it has the following disadvantages: limited by the low spectral resolution and spatial resolution of the greenhouse gas monitoring spectral band, the accuracy of obtaining greenhouse gas concentrations is low, and the temporal resolution is not high (revisit period of at least 3 days), which cannot fully meet the needs of timely obtaining 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. It is a 3-channel grating spectrometer with an orbit of about 700km. The operating wavelength range is 0.758um~2.08um, the spectral resolution is 0.044nm~0.1nm, the spatial resolution is 2km×2km, the scanning width is 20km@nadir, and it revisits at least once every 16 days. However, it has the following disadvantages: small scanning width (20km) and low temporal resolution (revisit at least once every 16 days). TANSO-FTS, launched by Japan in 2018 on GOSAT-02, is a 4-channel Fourier transform interferometer spectrometer with an orbital altitude of 613km, an operating wavelength range of 0.75um~14.3um, a spectral resolution of 0.04nm~5.52nm, a spatial resolution of 10.5km, a scanning width of 903km@nadir, and a revisit at least once every 3 days. However, it has the following disadvantages: low temporal resolution (revisit at least once every 3 days), isolated ground sampling points, and difficulty in obtaining spatially continuous greenhouse gas concentration information. Interferometers can only obtain spectral information of greenhouse gases by restoring interference patterns to spectrograms. It cannot image the detection area, that is, it cannot obtain specific spatial information, and can only obtain spatial spectral information. All of the above optical payloads for monitoring greenhouse gases have the following disadvantages: low temporal resolution, scan width less than 1000km, inability to meet global observation needs in a timely manner, and lack the ability to obtain global carbon flux and distribution change information in 1 day.To this end, an optical system is needed that can achieve high temporal resolution and wide-band global greenhouse gas monitoring, while ensuring high spatial resolution and spectral resolution, and has the characteristics of compact structure and small size.

[0004] like Figure 1 A spectroscopic system based on lens collimation and convergence is shown (originating from the American OCO-2 spectrometer): light passes through the first slit 11 and is irradiated onto the first collimating lens group 12. After being collimated, it is irradiated onto the plane grating 13. After being dispersed by the grating, the spectrum is irradiated onto the first converging lens group 14. After being converged, the spectrum is finally focused onto the first detector 15. The relative aperture of the incident end of the system is 1 / 1.8, and the front telescope system structure adopts the Cassegrain system, and its relative aperture is also 1 / 1.8. Although NASA's OCO-2 satellite has high spectral and spatial resolutions, its scanning width is small (20km@orbit altitude = 705km, which means a small field of view) and its temporal resolution is low (revisiting at least once every 16 days). In addition, the spectroscopic system is relatively large in size under the design of high spectral resolution and high light flux indicators (the optical path volume is length (1037mm) × width (410mm) × height (145mm)), and the collimating lens and converging lens must use multiple aspherical single lens pieces. In addition, the transmission structure generally has large stray light. Therefore, in order to avoid specular reflection of light on the lens surface, which increases the stray light of the system, it is necessary to coat each surface of each lens with an anti-reflection film (anti-reflection film). Therefore, it is difficult to meet the other party's requirements of small size, high temporal resolution, and relatively low cost in the design of the spectroscopic system based on lens collimation and convergence.

[0005] like Figure 2The structure of a spectroscopic system based on an immersion grating is shown (derived from the short-wave infrared spectrometer of the Tropomi payload of the European Space Agency): light passes through a second slit 31 and a long-pass filter 32 and is irradiated onto a plane reflector 33. After reflection, the light is irradiated onto a second collimating lens group 34. After collimation, the light is irradiated onto an immersion grating 35. After dispersion, the light spectrum is focused onto a second detector 37 through a second converging lens group 36. This spectroscopic system is generally used in the visible light and infrared bands. Although the volume of the spectroscopic system designed based on this structure is relatively small, in order to achieve good image quality of the system, the relative aperture of the front telescope system needs to match it and also use the same small relative aperture. In addition, there are multiple lenses in the collimating lens group and the converging lens group, resulting in low light energy utilization of the whole system. At the same time, the immersion grating needs to use a high number of lines and a high diffraction order, similar to the characteristics of the mid-step grating. In addition, the substrate material of the immersion grating is optical silicon, and the grating groove is a V-shaped groove. The groove formation generally requires reactive ion beam etching, which is Because the etching rate of silicon in pure physical ion impact is relatively slow, chemical reaction substances are often needed to assist in accelerating etching. Before etching, holographic exposure is required to make a grating mask. If the grating area is large, it often leads to uneven etching of the grating surface. Therefore, the production cost of this type of grating is high, and the production cycle is long, and the processing parameters need to be repeatedly adjusted. In addition, the spectral resolution of the short-wave infrared spectrometer is relatively low, about 0.25nm. Combined with the front telescope system, the spatial resolution of the entire system is only 7km×7km. The spectral resolution of high-precision monitoring of methane greenhouse gases is better than 0.2nm, and the spatial resolution is better than 7km. Most of the greenhouse gas monitoring spectrometers in Europe and the United States use immersion grating design, but my country is limited by the weak design and processing technology of this type of grating and has not achieved commercial product application.

[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@subsatellite point), temporal resolution (global monitoring in 1 day), large field of view (FOV≥100°), small size (less than length (470mm)×width (420mm)×height (260mm)), and is not restricted by the production of diffraction gratings. At the same time, the diffraction grating in this optical system also has the characteristics of high diffraction efficiency (more than 50%). Summary of the invention

[0007] In order to overcome the shortcomings of the prior art, the present invention provides a high-resolution spectral imaging device for monitoring atmospheric greenhouse gases, which has a small size, can achieve high resolution (combined with existing detector products, the spectral resolution (VIS-NIR) is 0.05nm~0.15nm; the spatial resolution is 2km×2km@orbit altitude=705km; the time resolution is 1 day to monitor the whole world) and meet the requirements of large field of view (FOV≥100°), and the grating has high diffraction efficiency (full-band absolute diffraction efficiency ≥50%), which is suitable for aviation and aerospace remote sensing applications.

[0008] In order to achieve the above object, the present invention adopts the following technical scheme: A high-resolution spectral imaging device for monitoring atmospheric greenhouse gases, comprising a small reflective off-axis front telescope system with a wide field of view and a spectral imager; The small reflective off-axis front telescope system with a wide field of view comprises an entrance pupil diaphragm, a first concave reflector, a first stray light elimination diaphragm, a folding reflector, a second stray light elimination diaphragm, a depolarizer, a convex reflector, a second concave reflector, and a color separation plate through which incident light sequentially passes; the color separation plate has a first surface that is a standard plane and a second surface that is a high-order aspheric surface according to the incident order of light, 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 comprises an incident slit, a filter, a first lens, an off-axis concave reflector, a plane grating, a folded plane mirror, a second lens, and a detector; light from two spectral band channels passes through their respective incident slits, filters, first lenses, off-axis concave reflectors, plane gratings, folded plane mirrors, and second lenses in sequence, and is focused onto their respective detectors.

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

[0010] Further, the first concave reflector is a concave spherical surface reflector; the folding reflector is a reflective Schmidt correction plate; the depolarizer is a spatial pseudo depolarizer; the convex reflector is a convex secondary aspheric surface; the second concave reflector is a concave secondary aspheric surface; Furthermore, the incident slit is a curved slit, which is used to correct the spatial distortion of the final imaging surface of the system; the filter is a single-pass filter, which is used to eliminate interfering light other than the used wavelength and reduce the stray light of the optical system; the first lens is an off-axis lens; the off-axis concave reflector is an off-axis aspheric reflector; the plane grating is a holographic plane grating; the second lens is an off-axis lens; and the detector is a planar array detector.

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

[0012] Furthermore, the incident slit, the filter, the first lens, the off-axis concave reflector, the folding 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 1st order, and the absolute diffraction efficiency in the working band is above 50% in a state close to Littrow.

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

[0015] Furthermore, the spectral imager is applicable to the following spectral bands: 0.75-0.774um, 1.6-1.622um, 2.045-2.085um, 2.3-2.345um.

[0016] Furthermore, the incident light passes through the incident slit and the filter and illuminates the first lens. After passing through the first lens, it illuminates the off-axis concave reflector, and the incident light is guided to the reflective plane grating. The dispersed light is dispersed by the plane grating and is close to the Littrow state and illuminates back to the off-axis concave reflector, so that the dispersed spectrum converges and illuminates the return mirror, and then illuminates the second lens after reflection. After passing through, the spectrum is further focused onto the detector.

[0017] In the present invention, the same center plane refers to the YOZ plane of the optical system; The small reflective off-axis front telescope system with a wide field of view is used to receive incident light from a light source, and transmit the incident light sequentially through the entrance pupil diaphragm, the first concave reflector, the first stray light elimination diaphragm, the folding reflector, the second stray light elimination diaphragm, the depolarizer, the convex reflector, the second concave reflector, the color separation plate, and finally to the entrance slit of the spectral imager; The incident light passing through the incident slit is irradiated to the first lens through the filter, and the filter is used to remove interference light other than the used wavelength and reduce the stray light of the optical system; The first lens is used to offset the optical path to adjust the distance between the light passing through it and the plane grating to avoid interference between the two, and to correct system aberrations. The incident light passes through the first lens and is transmitted to the off-axis concave reflector; The off-axis concave reflector is used to collimate the incident light and correct the system aberration, and guide the incident light onto the plane grating; The plane grating separates different wavelengths in the incident light into a spectrum through the dispersion characteristics of the diffraction grating, and the spectrum is transmitted back to the off-axis concave reflector in a state close to Littrow, so as to converge the spectral lines and correct the system aberration, and the spectrum is transmitted to the folding reflector; The folding reflector is used to fold back the optical path and reduce the volume of the optical path, and the spectrum is transmitted to the second lens through the folding reflector; The second lens is used to further converge the spectral line and correct the system aberration, 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 plane grating is a holographic diffraction grating according to the manufacturing process, the groove shape of the plane grating is sinusoidal, and the absolute diffraction efficiency is above 50% in the working band under a state close to Littrow.

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

[0020] Preferably, the emission direction of the 0th order light (ie, reflected light) of the plane grating deviates from the detector and the concave reflector.

[0021] Preferably, the incident light is transmitted to the plane grating in a nearly collimated manner after passing through the off-axis concave reflector.

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

[0023] The beneficial effects of the present invention compared with the prior art are: (1) The present invention has a compact structure and can be made small in size. It can also 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 plane diffraction grating in the present invention is a holographic grating with low stray light, high dispersion, high diffraction efficiency, and easy production.

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

[0026] (4) In the present invention, the 0th order light (i.e., reflected light) of the plane diffraction grating deviates from the detector and the off-axis concave reflector, and the 0th order light is easily blocked, thereby effectively reducing the stray light of 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 with most previous designs, the present invention is easier to achieve high temporal resolution and wide-band global greenhouse gas monitoring of the system, while ensuring high spatial resolution and spectral resolution, and has a compact structure, small size, high diffraction efficiency of the grating, low stray light optical design, and a large detection width. The present invention has the characteristics of 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 aviation and aerospace remote sensing. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a typical design diagram of a spectroscopic system based on an immersion grating according to the prior art; Figure 2 It is a typical design diagram of a light splitting system based on lens collimation and convergence according to the prior art; Figure 3 It is a structural schematic diagram of a high-resolution spectral imaging system for monitoring atmospheric greenhouse gases of the present invention; Figure 4 It is a schematic diagram of a dual-channel spectral imaging device with a full field of view of 120° and a color separation filter (its system relative aperture 1 / F#=1 / 3) of the present invention; Figure 5 is a schematic diagram of a dual-channel spectral imaging device showing a light trap in the form of a physical barrier for shielding a diffraction grating 0-order light according to an embodiment of the present invention; Figure 6 It is a schematic diagram of a dual-channel spectral imaging device for working wavelengths in the range of 0.75 to 0.774 um and 1.6 to 1.622 um and having a relative aperture of 1 / F#=1 / 4 according to an embodiment of the present invention; Figure 7 It is a schematic diagram of a dual-channel spectral imaging device for working wavelength ranges of 2.045-2.085um and 2.3-2.345um and having a relative aperture of 1 / F#=1 / 3.2 according to an embodiment of the present invention; Figure 8 yes Figure 6 The embodiment provides a diffraction efficiency curve of a diffraction grating with an operating wavelength of 0.75 to 0.774 μm; Fig. 9 yes Figure 6 The embodiment provides a diffraction efficiency curve of a diffraction grating with an operating wavelength of 1.6 to 1.622 um; Fig.10 yes Figure 7The embodiment provides a diffraction efficiency curve of a diffraction grating with an operating wavelength of 2.045 to 2.085 um; Fig.11 yes Figure 7 The embodiment provides a diffraction efficiency curve of a diffraction grating with an operating wavelength of 2.3 to 2.345 μm; Wherein, the accompanying drawings are marked as follows: A first slit 11, a first collimating lens group 12, a plane grating 13, a first converging lens group 14, a first detector 15, and a sawtooth light trap 16; A second slit 31, a long pass filter 32, a plane reflector 33, a second collimating lens group 34, an immersion grating 35, a second converging lens group 36, and a second detector 37; Entrance pupil diaphragm 1, first concave reflector 2, first stray light elimination diaphragm 3, folding reflector 4, second stray light elimination diaphragm 5, depolarizer 6, convex reflector 7, aperture diaphragm 8, second concave reflector 9, color separation film 10; Channel 1 incident slit 41, channel 1 filter 42, channel 1 first lens 43, channel 1 off-axis concave reflector 44, channel 1 holographic plane grating 45, channel 1 folding plane mirror 46, channel 1 second lens 47, channel 1 detector 48; Channel two incident slit 21, channel two filter 22, channel two first lens 23, channel two off-axis concave reflector 24, channel two holographic plane grating 25, channel two folding plane mirror 26, channel two second lens 27, channel two detector 28, light trap 29. DETAILED DESCRIPTION

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

[0031] exist Figures 3 to 7In the embodiment shown, a high-resolution spectral imaging system for monitoring atmospheric greenhouse gases is demonstrated, which is used for monitoring spectral imaging analysis of atmospheric greenhouse gases. The incident light sequentially passes through the entrance pupil diaphragm 1, the first concave reflector 2, the first stray light elimination diaphragm 3, the folding reflector 4, the second stray light elimination diaphragm 5, the depolarizer 6, the convex reflector 7, the aperture diaphragm 8, and the second concave reflector 9 in the wide-field small reflective off-axis front telescope system, and is divided into reflected light and transmitted light after passing through the color separation plate 10. The reflected light passes through the channel-one incident slit 41, the channel-one filter 42, and the channel-one first lens 43, and then irradiates the channel-one off-axis concave reflector 44, which guides the incident light to the channel-one holographic plane grating 45, and is dispersed by the diffraction grating. The dispersed light is close to the Littrow-shaped The light is in the state of Littrow state, and is irradiated back to the off-axis concave reflector 44 of channel one, so that the dispersed spectrum is converged and irradiated to the folding plane mirror 46 of channel one, and is reflected and irradiated to the second lens 47 of channel one. After passing through, the spectrum is further focused on the detector 48 of channel one, while the transmitted light passes through the incident slit 21 of channel two, the filter 22 of channel two, and the first lens 23 of channel two, and is then irradiated to the off-axis concave reflector 24 of channel two, which guides the incident light to the holographic plane grating 25 of channel two, and is dispersed by the diffraction grating. The dispersed light is close to the Littrow state, and is irradiated back to the off-axis concave reflector 24 of channel two, so that the dispersed spectrum is converged and irradiated to the folding plane mirror 26 of channel two, and is reflected and irradiated to the second lens 27 of channel two. After passing through, the spectrum is further focused on the detector 28 of channel two.

[0032] The detector 48 of channel one and the incident 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 incident slit 21 of channel two are located on the same side of the holographic plane grating 25 of channel two. This spectroscopic structure can greatly reduce the volume of the optical path structure of the system, and at the same time, it is easy to achieve high spectral resolution, high light flux, and low stray light of the system; in addition, the holographic diffraction grating with a sinusoidal groove shape in the spectroscopic system also has a high diffraction efficiency (≥50%), and these designs are relative to the following: Figure 1 The design of the spectroscopic system based on lens collimation and convergence has significant advantages.

[0033] like Figure 2As shown, the spectroscopic system based on the immersion grating includes a second collimating lens group 34 and a second converging lens group 36. Although the volume of the spectroscopic system based on this structural design is relatively small, in order to achieve good image quality of the system, the incident end of the spectroscopic system can only use a small relative aperture (1 / 8~1 / 10), and multiple lenses are used in the second collimating lens group 34 and the second converging lens group 36, resulting in low light energy utilization of the whole system. At the same time, the immersion grating 35 needs to use a high number of lines, and the substrate material of the immersion grating 35 is optical material silicon, and the grating groove is a V-shaped groove, which makes the grating processing and manufacturing process relatively complicated. Figure 3 The embodiment shown is a schematic structural diagram of a spectral imaging device for displaying spectral analysis of atmospheric greenhouse gases, comprising an entrance pupil diaphragm 1, a first concave reflector 2, a first stray light elimination diaphragm 3, a folding reflector 4, a second stray light elimination diaphragm 5, a depolarizer 6, a convex reflector 7, an aperture diaphragm 8, a second concave reflector 9, a color separation plate 10, an incident slit 41 for channel one, a filter 42 for channel one, a first lens 43 for channel one, an off-axis concave reflector 44 for channel one, a holographic plane grating 45 for channel one, a folding plane mirror 46 for channel one, a second lens 47 for channel one, and a detector 48 for channel one; an incident slit 21 for channel two, a filter 22 for channel two, a first lens 23 for channel two, an off-axis concave reflector 24 for channel two, a holographic plane grating 25 for channel two, a folding plane mirror 26 for channel two, a second lens 27 for channel two, and a detector 28 for channel two, and the YOZ plane is the central plane of the optical system. Among them, the channel one detector 48 and the channel one incident slit 41 are located on the same side of the channel one holographic plane grating 45, the channel two detector 28 and the channel two incident slit 21 are located on the same side of the channel two holographic plane grating 25, the dispersed light of the channel one holographic plane grating 45 in the channel one reflective spectroscopic imager is transmitted back to the channel one off-axis concave reflector 44 in a state close to Littrow in the YOZ plane, and finally converges on the channel one detector 48, and the diffracted light of the channel two holographic plane grating 25 in the channel two reflective spectroscopic imager is transmitted back to the channel one off-axis concave reflector 24 in a state close to Littrow in the YOZ plane, and finally converges on the channel two detector 28.

[0034] In the spectroscopic system, the off-axis concave reflector 44 of channel 1 and the off-axis concave reflector 24 of channel 2 are preferably non-spherical surfaces, which can easily achieve high-quality image quality of the system. The grating stripe groove type of the holographic plane grating 45 of channel 1 and the holographic plane grating 25 of channel 2 is preferably a sinusoidal equidistant linear groove holographic grating, which is easy to process and manufacture, and can also be a blazed type. The detector 48 of channel 1 and the detector 28 of channel 2 are of a planar array type, and the planar array type can be selected from HAWAII H2RG, CCD42-40, CCD55-30 of Teledyne e2v or 1280SCICAM of Princeton Infrared Technologies.

[0035] In the spectroscopic system, in order to maximize the energy of the beam using the first-order dispersed light and reduce the influence of the system stray light, it is completed by approaching the Littrow state. For the system stray light, it 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 spectroscopic system uses the first-order diffraction order of the grating, when the grating incident angle a, the wavelength λ, and the number of grating lines f satisfy formula (1): |1-λf|<sin(a)<2λf-1 (1) At this time, there are only the first-order diffraction and zero-order light, and no other diffraction orders exist, which is beneficial to reduce stray light in the optical system. At the same time, the appropriate groove depth is selected to make the spectrum of the first-order dispersion have a higher diffraction efficiency, especially when 0.7﹤λf﹤1.2, the average diffraction efficiency of the two polarizations can reach more than 50%, which is beneficial to improve the signal-to-noise ratio of the spectral instrument.

[0036] like Figure 4An embodiment of the present invention is shown, which is a dual-channel spectral imaging device with a field of view of FOV=120° and a color separation film that can be used for monitoring atmospheric greenhouse gas analysis. The color separation film 10 allows the system's operating wavelength to be divided into a visible light band of 540nm to 570nm and a visible light band of 750nm to 774nm. The relative aperture of the system is 1 / F#=1 / 3, and 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 ability to collect light. The channel 1 incident slit 41 and the channel 2 incident slit 21 are both curved slits with a height of 26mm and a width of 50um. The channel 1 detector 48 and the channel 2 detector 28 both use CCD55-30 (pixel size is 22.5um×22.5um) from Teledyne e2v. Among them, the channel 1 incident slit 41, channel 1 filter 42, channel 1 folding plane mirror 46, channel 1 second lens 47, channel 1 detector 48 are all located at the same side below the channel 1 holographic plane grating 45; the channel 2 incident slit 21, channel 2 long pass filter 22, channel 2 folding plane mirror 26, channel 2 second lens 27, channel 2 detector 28 are all located at the same side below the channel 2 holographic plane grating 25, making the optical system structure more compact, and its optical path volume length × width × height is: 465 × 418 × 264 mm. The spectrum length of the spectroscopic system = 25.0 mm, and the spectrum resolution is 0.05 nm @ 760 nm.

[0037] like Figure 5 As shown, stray light can be eliminated by setting a light trap 29. For example, in the system, the incident light is collimated by the off-axis concave reflector 44 of channel one and then irradiated on the holographic plane grating 45 of channel one, and the incident light is collimated by the off-axis concave reflector 24 of channel two and then irradiated on the holographic plane grating 25 of channel one. After the grating diffraction, there are zero-order light and first-order dispersion spectrum, which is known to those skilled in the art. The zero-order light is not needed by the system. If it is not blocked, it will become stray light. The sawtooth light trap minimizes the scattering of light. Figure 5 A plurality of serrated light traps 16 (indicated by thick black lines) may be provided around the light propagation path in order to eliminate the zeroth order light and other stray light.

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

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

[0040] like Figure 8 As shown, Figure 6 The absolute diffraction efficiency diagram of the holographic plane grating of the channel 1 of the spectroscopic system of the embodiment, the holographic plane grating has 2224 lines / mm, the grating groove shape is sinusoidal, the grating incident angle is 53.29°, and the diffraction level used is -1. Figure 8 It can be seen that in the working 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 the high-resolution spectral imaging system used to monitor atmospheric greenhouse gases.

[0041] like Fig. 9 As shown, Figure 6 The absolute diffraction efficiency diagram of the holographic plane grating of channel 2 of the spectroscopic system of the embodiment, the holographic plane grating has 1058 lines / mm, the grating groove shape is sinusoidal, the grating incident angle is -54.37°, and the diffraction level used is -1. Fig. 9 It can be seen that in the working wavelength range of 1600nm to 1622nm, the absolute diffraction efficiency of the grating is above 52%, which is beneficial to improve the signal-to-noise ratio of the high-resolution spectral imaging system used to monitor atmospheric greenhouse gases.

[0042] like Fig.10 As shown, Figure 7 The absolute diffraction efficiency diagram of the holographic plane grating of the channel 1 of the spectroscopic system of the embodiment, the holographic plane grating has 816 lines / mm, the grating groove shape is sinusoidal, the grating incident angle is 53.65°, and the diffraction level used is -1. Fig.10 It can be seen that in the working 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 the high-resolution spectral imaging system used to monitor atmospheric greenhouse gases.

[0043] like Fig.11 As shown, Figure 7 The absolute diffraction efficiency diagram of the holographic plane grating of channel 2 of the spectroscopic system of the embodiment, the holographic plane grating has 746 lines / mm, the grating groove shape is sinusoidal, the grating incident angle is -54.60°, and the diffraction level used is -1. Fig.11 It can be seen that in the working 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 the high-resolution spectral imaging system used to monitor atmospheric greenhouse gases.

[0044] Table 1 and Table 2 below provide examples of analysis systems for monitoring atmospheric greenhouse gases (eg Figure 6 ) and other optical parameters, and provides a description of a typical system known to those skilled in the art.

[0045] Table 1 Example optical specifications (channel 1)

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

[0047] In each embodiment, the incident slit, long-pass filter, first lens, second lens, off-axis concave reflector, and detector in the improved optical design are all located on the same side below the holographic plane grating. This design makes the optical path structure more compact, and the space occupied is significantly smaller, which is beneficial to the spatial arrangement and weight reduction of the spectral imaging instrument. The absolute diffraction efficiency of the sinusoidal groove holographic plane grating in each embodiment is above 50%, which is beneficial to the signal-to-noise ratio of the spectral imaging instrument.

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

Claims

1. A high-resolution spectral imaging device for monitoring atmospheric greenhouse gases, It is characterized in that It includes a small reflective off-axis front telescope system with a wide field of view and a spectral imager; The small reflective off-axis front telescope system with a wide field of view comprises an entrance pupil diaphragm, a first concave reflector, a first stray light elimination diaphragm, a folding reflector, a second stray light elimination diaphragm, a depolarizer, a convex reflector, a second concave reflector, and a color separation plate through which incident light sequentially passes; the color separation plate has a first surface that is a standard plane and a second surface that is a high-order aspheric surface according to the incident order of light, 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 comprises an incident slit, a filter, a first lens, an off-axis concave reflector, a plane grating, a folded plane mirror, a second lens, and a detector; light from two spectral band channels passes through their respective incident slits, filters, first lenses, off-axis concave reflectors, plane gratings, folded plane mirrors, and second lenses in sequence, and is focused onto their respective detectors.

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

3. A high-resolution spectral imaging device for monitoring atmospheric greenhouse gases according to claim 1, It is characterized in that The incident slit is a curved slit, which is used to correct the spatial distortion of the final imaging surface of the system; the filter is a single-pass filter, which is used to eliminate interfering light other than the used wavelength and reduce the stray light of the optical system; the first lens is an off-axis lens; the off-axis concave reflector is an off-axis aspheric reflector; the plane grating is a holographic plane grating; the second lens is an off-axis lens; and the detector is a planar array detector.

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

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

6. A high-resolution spectral imaging device for monitoring atmospheric greenhouse gases according to claim 5, Features: The groove shape of the diffraction grating is sinusoidal, the working diffraction order is 1st order, and the absolute diffraction efficiency in the working band is above 50% in a state close to Littrow.

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

9. A high-resolution spectral imaging device for monitoring atmospheric greenhouse gases according to claim 1, Features: The incident light passes through the incident slit and the filter and illuminates the first lens. After passing through the first lens, it illuminates the off-axis concave reflector, which guides the incident light to the reflective plane grating. After being dispersed by the plane grating, the dispersed light is close to the Littrow state and illuminates back to the off-axis concave reflector, so that the dispersed spectrum converges and illuminates the return mirror, and then illuminates the second lens after reflection. After passing through, the spectrum is further focused onto the detector.

10. A high-resolution spectral imaging device for monitoring atmospheric greenhouse gases according to claim 1, Features: The plane grating is located on one side of the incident slit, the first lens and the off-axis concave reflecting mirror.

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