A wide coverage and high resolution greenhouse gas imaging spectrometer and its application

Abstract

The present invention discloses a wide coverage, high-resolution greenhouse gas imaging spectrometer and its application. The optical system of the spectrometer includes a reflective front telephoto objective and a collimating lens, as well as a multi-channel independent spectroscopic imaging device. Multiple spectral channels share the front telephoto objective and the collimating lens, and there is no need to consider the spatial alignment problem. The structure is a three-reflector structure; the spectroscopic device adopts a near-Littrow mount, prism + prism grating + prism structure, with a reflective immersion grating for spectrometry, and a wedge prism to assist in dispersion and distortion correction; the imaging device adopts a transmission Pittswan structure. The spectrometer provided by the present invention has the advantages of wide coverage, low distortion, large relative aperture, high transmittance, and high resolution, and can be used for high-precision quantitative detection of four different types of greenhouse gas concentrations at the same time.

Description

Technical Field

[0001] The present invention relates to an imaging spectrometer, and in particular to an imaging spectrometer suitable for high-precision remote sensing detection of atmospheric greenhouse gas concentrations and its application, which has the characteristics of wide coverage, low distortion, large relative aperture, high resolution and high spectral resolution. Background Art

[0002] In recent years, atmospheric environmental problems have become increasingly prominent, and the impact of climate change has gradually intensified, which has become a hot topic of global concern. CO2 and CH4 in the atmosphere contribute the most to radiative forcing and are the main greenhouse gases causing global warming. Therefore, reducing the emission of these gases is called one of the most significant environmental challenges of the 21st century. Through intensive temporal and spatial sampling, using satellites to measure the distribution of global atmospheric greenhouse gas concentrations can deepen the understanding of natural and anthropogenic surface carbon fluxes. At present, the United States, Europe, Japan, China and other countries with great influence and research capabilities in the world are actively developing and manufacturing equipment for monitoring and analyzing changes in global greenhouse gas distribution.

[0003] The OCO / OCO-2 satellites developed by the United States and the TANSAT satellite developed by China have verified the feasibility of using plane gratings to detect atmospheric carbon dioxide concentrations and have realized their applications in space. However, due to the large distortion of the gratings, low diffraction efficiency, and the ability to detect only TM polarization state information, these two greenhouse gas spectrometers have low overall energy utilization and small ground coverage. The greenhouse gas detector TANSO-FTS on the Japanese GOSAT satellite uses a Fourier transform interferometer spectrometer, which also achieves high-precision detection of atmospheric greenhouse gases. However, its ground sampling points are isolated areas, making it difficult to obtain spatially continuous CO2 concentration information. Therefore, there is a strong demand and prospect for the development of greenhouse gas imaging spectrometers with wide coverage, high imaging performance, high transmittance, high resolution, and high precision. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a greenhouse gas imaging spectrometer for remote sensing detection, which has high imaging performance, low distortion, wide coverage, high transmittance and high resolution characteristics, and its application.

[0005] To achieve the above-mentioned purpose of the invention, the technical solution adopted by the present invention is to provide a wide coverage high-resolution greenhouse gas imaging spectrometer, whose optical system includes a front telescope objective, a collimating lens and four spectroscopic imaging devices, and the F number of the system ranges from 1.2 to 1.8; according to the incident direction of the light, the light enters the front telescope objective through the aperture diaphragm, is imaged at the slit, is collimated into a parallel light beam by the collimating lens, is divided into four different detection bands by the dichroic color separation plate, enters four spectroscopic imaging devices respectively for spectroscopic dispersion, and is imaged on the detector through the imaging lens group;

[0006] The front telescope objective lens is a coaxial biased field three-reflection structure with an intermediate real image, which is a primary mirror, a secondary mirror and a third mirror in sequence, the aperture stop is located in front of the primary mirror, and the intermediate real image is located between the primary mirror and the secondary mirror, close to the secondary mirror; one or two of the reflectors are aspherical;

[0007] The collimating lens is a coaxial partial field three-reflection structure with an intermediate real image, which includes a collimating lens primary mirror, a collimating lens secondary mirror and a collimating lens third mirror in sequence, and the intermediate real image is located between the collimating lens secondary mirror and the collimating lens third mirror, close to the collimating lens secondary mirror; one or two of the reflectors are aspherical;

[0008] The spectroscopic imaging device is a near-Littrow mount, which comprises a first wedge-shaped prism, a reflective immersion grating and a second wedge-shaped prism in sequence.

[0009] The invention provides a wide coverage high-resolution greenhouse gas imaging spectrometer, which has a spectral resolution of 18000 to 25000, a spatial resolution of 1km to 5km, and a width of 100km to 300km.

[0010] The reflective immersion grating of the present invention has an immersion medium comprising fused quartz, high refractive index glass or silicon; the grating is a rectangular groove grating, and the diffraction efficiency is above 80% in the working band; the imaging lens group is a transmission Petzwan structure, and the F number ranges from 1.2 to 1.8; the F number ranges from 1.8 to 4 for the front telescope objective lens and the collimating lens.

[0011] The technical solution of the present invention also includes the application of the above-mentioned wide coverage high-resolution greenhouse gas imaging spectrometer, and different working bands are set according to the detection target: oxygen-A (O2-A) absorption band 0.7525~0.7675μm, weak carbon dioxide (CO2) absorption band 1.595~1.625μm, strong carbon dioxide (CO2) absorption band 2.04~2.08μm, methane (CH4) absorption band 2.275~2.325μm, through four independently set spectroscopic imaging devices, it is used to simultaneously detect four different types of greenhouse gases.

[0012] Compared with the prior art, the present invention has the following beneficial effects:

[0013] 1. The wide coverage and high resolution greenhouse gas imaging spectrometer of the present invention can simultaneously monitor the concentrations of atmospheric carbon dioxide and methane, etc., and has a wide ground coverage range, a large relative aperture, high detection accuracy, and high spatial resolution and spectral resolution.

[0014] 2. Imaging spectrometers share the front telescope objective and collimating lens, so there is no need to consider spatial alignment issues. They all adopt a three-mirror structure, have no chromatic aberration, and are suitable for wide bands.

[0015] 3. The spectroscopic imaging device adopts a reflective immersion grating, supplemented by a wedge-angle prism to correct distortion, which can achieve low distortion, low polarization, and small volume design to meet different application scenarios.

[0016] 4. Each working band uses an independent spectroscopic imaging device with a narrow band range, small material dispersion, and is designed using the same type of glass. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a schematic structural diagram of an optical system of a wide-coverage, high-resolution greenhouse gas imaging spectrometer provided in Example 1 of the present invention;

[0018] Figure 2 is a schematic diagram of a reflective rectangular groove immersion grating provided in Example 1 of the present invention;

[0019] Figure 3 is the diffraction efficiency curve of the O2-A band reflective rectangular groove immersion grating provided in Example 1 of the present invention;

[0020] Figure 4 is a spectral bending curve diagram of the O2-A band optical system provided by Example 1 of the present invention;

[0021] Figure 5 is a color distortion curve diagram of the O2-A band optical system provided in Example 1 of the present invention;

[0022] In the figure: 1. aperture stop; 2. front telescope objective primary mirror; 3. front telescope objective secondary mirror; 4. front telescope objective tertiary mirror; 5. slit; 6. collimator lens primary mirror; 7. collimator lens secondary mirror; 8. collimator lens tertiary mirror; 9. dichroic color separation plate; 10. spectroscopic imaging device system; 11. grating incident light; 12. grating diffracted light; 13. prism front surface (grating entrance / exit surface); 14. prism back surface (grating surface); 15. wedge prism / group (1); 16. wedge prism / group (2); 17. reflective immersion grating; 18. imaging mirror group; 19. detector. DETAILED DESCRIPTION

[0023] The embodiments of the invention will be further described in detail below with reference to the accompanying drawings and examples.

[0024] Example 1

[0025] The technical solution provided in this embodiment is a wide coverage high-resolution greenhouse gas imaging spectrometer, whose working band is oxygen-A (O2-A) absorption band 0.7525~0.7675μm, weak carbon dioxide (CO2) absorption band 1.595~1.625μm, strong carbon dioxide (CO2) absorption band 2.04~2.08μm, methane (CH4) absorption band 2.275~2.325μm. The ground swath width is 102km, the field of view angle is 7°, the ground space sampling range is 3km×3km, the spectral resolution is 19000~23000, the front telescope objective lens and collimating lens F number is 3, and the imaging device lens group F number is 1.8. Since the structures of the four working bands of spectroscopic imaging devices are similar, this embodiment takes the O2-A absorption band 0.7525~0.7675μm optical system as an example for explanation.

[0026] See attached Figure 1 , which is a schematic diagram of the optical system structure of the wide coverage high resolution greenhouse gas imaging spectrometer provided in this embodiment, including an aperture stop 1, a primary mirror 2 of a front telescope objective lens, a secondary mirror 3, a third mirror 4, a slit 5, a primary mirror 6 of a collimating lens, a secondary mirror 7, a third mirror 8, a dichroic color separation plate 9, and a spectroscopic imaging device system 10, wherein the spectroscopic imaging device is independently set according to different working bands of the detection target, and the spectroscopic imaging device of each band has a similar structure, and is respectively composed of a wedge prism / group (1) 15, a wedge prism / group (2) 16, a reflective immersion grating 17, an imaging lens group 18 and a detector 19. The spectroscopic imaging device adopts a reflective immersion grating 17 for dispersion, and the immersion medium is fused silica. The wedge prisms / groups 16 and 18 are used to correct distortion and assist dispersion. The imaging lens group adopts a four-piece Petzwan type structure with an F number of 1.8. The focal length of the imaging lens group used in the O2-A absorption band is 145mm, and the glass material is fused quartz.

[0027] The front telescope objective lens of the wide coverage high-resolution greenhouse gas imaging spectrometer provided in this embodiment includes an aperture stop 1, a front telescope objective lens primary lens 2, a front telescope objective lens secondary lens 3, a front telescope objective lens third lens 4 and a slit 5. The structure adopts a coaxial biased field three-reflection structure with an intermediate real image, and the intermediate real image is located between the primary and secondary mirrors, close to the secondary mirror; the primary three mirrors are two aspherical reflectors, and the secondary mirror is a spherical reflector; the front telescope objective lens has an F number of 3, a focal length of 100mm, and the vertex curvature radii of the three reflectors are 218mm, 103mm and 180mm respectively. The primary three mirrors are ellipsoidal surfaces, and the secondary aspheric coefficients are -0.58 and -0.02 respectively. The slit 5 is an air slit, which is made of ion beam etched silicon wafer, is 13mm long, 45μm±1μm wide, and is perpendicular to the paper surface.

[0028] The optical path of the collimating lens of the wide coverage high-resolution greenhouse gas imaging spectrometer provided in this embodiment is composed of a slit 5, a collimating lens primary mirror 6, a collimating lens secondary mirror 7 and a collimating lens third mirror 8. The structure adopts a coaxial biased field three-reflection structure with an intermediate real image, and the intermediate real image is located between the secondary three mirrors and close to the secondary mirror; the primary three mirrors are two aspherical reflectors, and the secondary mirror is a spherical reflector; the F number of the collimating lens is 3, the focal length is 250 mm, the vertex curvature radii of the three reflectors are 262 mm, 184.5 mm and 502 mm respectively, the primary three mirrors are all ellipsoidal surfaces, and the secondary aspheric coefficients are -0.03 and -0.70 respectively.

[0029] See attached Figure 2 , which is a schematic diagram of a reflective rectangular groove quartz immersion grating of a wide coverage high-resolution greenhouse gas imaging spectrometer provided in this embodiment, the grating incident light 11 and the grating diffracted light 12 share the prism front surface (grating entrance / exit surface) 13, and are diffracted and reflected on the prism rear surface (grating surface) 14. The grating groove is a rectangular groove, the immersion medium is fused quartz, and the surface is coated with a silver film.

[0030] See attached Figure 3 , which is a graph of the diffraction efficiency of the O2-A band immersion grating of the wide coverage high-resolution greenhouse gas imaging spectrometer provided in this embodiment. It can be seen from the graph that the average diffraction efficiency is higher than 85%, and the absolute polarization values ​​of the TE and TM modes are less than 10%.

[0031] See attached Figure 4 and 5 , are respectively a spectral line bending curve diagram and a color distortion curve diagram of the O2-A band optical system of the wide coverage high-resolution greenhouse gas imaging spectrometer provided in this embodiment. The abscissa is the normalized field of view coordinate, and the ordinate represents the distortion amount. It can be seen from the figure that the maximum spectral line bending of the spectrometer system is about 4.3μm, and the maximum color distortion is about 9.1μm.

[0032] The spectrometer optical system provided in this embodiment can set different working bands according to the detection target: oxygen-A (O2-A) absorption band 0.7525~0.7675μm, weak carbon dioxide (CO2) absorption band 1.595~1.625μm, strong carbon dioxide (CO2) absorption band 2.04~2.08μm, methane (CH4) absorption band 2.275~2.325μm, through four independently set spectroscopic imaging devices, it is used to simultaneously detect four different types of greenhouse gases.

Claims

1. A wide coverage and high resolution greenhouse gas imaging spectrometer, characterized in that: Its optical system includes a front telescope objective lens, a collimating lens and four spectroscopic imaging devices, and the F number of the system ranges from 1.2 to 1.

8. According to the incident direction of the light, the light enters the front telescope objective lens through the aperture diaphragm (1), is imaged at the slit (5), is collimated into a parallel light beam by the collimating lens, is divided into four different detection bands by a dichroic color separation plate (9), respectively enters four spectroscopic imaging devices for spectroscopic dispersion, and is then imaged on a detector (19) through an imaging lens group (18); The front telephoto objective lens is a coaxial biased field three-reflection structure with an intermediate real image, which is composed of a primary mirror (2), a secondary mirror (3) and a third mirror (4) in sequence; the aperture stop (1) is located in front of the primary mirror (2); the intermediate real image is located between the primary mirror (2) and the secondary mirror (3), close to the secondary mirror (3); one or two of the reflectors are aspherical; The collimating lens is a coaxial, biased-field three-reflection structure with an intermediate real image, which comprises a collimating lens primary mirror (6), a collimating lens secondary mirror (7) and a collimating lens third mirror (8) in sequence, wherein the intermediate real image is located between the collimating lens secondary mirror (7) and the collimating lens third mirror (8), close to the collimating lens secondary mirror (7); one or two of the reflectors are aspherical surfaces; The spectroscopic imaging device is a near-Littrow mount, which comprises a first wedge-shaped prism (15), a reflective immersion grating (17) and a second wedge-shaped prism (16) in sequence; Different working bands are set according to the detection target: oxygen-A (O2-A) absorption band 0.7525~0.7675μm, weak carbon dioxide (CO2) absorption band 1.595~1.625μm, strong carbon dioxide (CO2) absorption band 2.04~2.08μm, methane (CH4) absorption band 2.275~2.325μm, through four independently set spectroscopic imaging devices, used to simultaneously detect four different types of greenhouse gases; The reflective immersion grating, the immersion medium includes fused quartz, high refractive index glass or silicon; the grating is a rectangular groove grating, and the diffraction efficiency is more than 80% within the working band; The grating incident light (11) and the grating diffracted light (12) share the prism front surface (13), i.e., the grating entrance / exit surface, and are diffracted and reflected on the prism rear surface (14), i.e., the grating surface.

2. A wide coverage high resolution greenhouse gas imaging spectrometer according to claim 1, characterized in that: Its spectral resolution is 18,000 to 25,000, its spatial resolution is 1 km to 5 km, and its bandwidth is 100 km to 300 km.

3. The wide coverage and high resolution greenhouse gas imaging spectrometer according to claim 1, characterized in that: The imaging lens group is a transmissive Petzwan structure, and the F number ranges from 1.2 to 1.

8.

4. The wide coverage and high resolution greenhouse gas imaging spectrometer according to claim 1, characterized in that: The F number of the front telephoto objective lens and the collimating lens ranges from 1.8 to 4.

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