Large-relative-aperture multichannel wide-width greenhouse gas detection spectrometer optical system

Abstract

The invention relates to an optical system of a large-relative-aperture multi-channel wide-width greenhouse gas detection spectrometer. The optical system comprises a front-end telescopic system, a collimating lens group and a rear-end five-channel, the front-end telescopic system is of an off-axis two-reflector structure; the collimating lens group is a focusing refraction lens group taking the slit as a focus; the five channels at the rear end realize pupil matching of the splicing system with wide width and large relative aperture by using a beam splitter; the dispersion element of each channel is a transmission grating, and the focus lens group is of an off-axis two-reflector structure; and the beam splitter is a prism beam splitting system formed by splicing right-angle prism groups. A broadband crossing detection design is completed by using a reflective structure and an achromatic theory, and a prism beam splitting group is designed to complete system integration. The optical system provided by the invention integrates the detection characteristics of large relative aperture, wide width, high spatial resolution and multiple gas channels, can simultaneously monitor various gases homologous with artificial carbon emission, and realizes collaborative observation, thereby accurately measuring and calculating an artificial active carbon emission source.

Description

Technical Field

[0001] The present invention belongs to the technical field of spectrometer design, and particularly relates to an optical system of a large relative aperture multi-channel wide-width greenhouse gas detection spectrometer. Background Art

[0002] Due to human activities such as fossil fuel combustion and land use change, the concentration of carbon dioxide (CO2) has increased by more than 40%. Therefore, with the development of carbon satellite payloads, the actual demands for precise detection and wide-area high-efficiency detection of carbon emissions from human activities have put forward new index requirements for carbon satellite payloads.

[0003] The existing technical solutions of greenhouse gas detection imaging spectrometers can be divided into two types according to their detection characteristics. The first type of solution takes the Tansat carbon satellite as an example. It realizes large relative aperture hyperspectral greenhouse gas detection. Tansat carries an ultra-high spectral resolution grating spectrometer and a cloud and aerosol polarization imager. Its orbital altitude is 708 km, the swath is 20 km, the F number is 2, and the spatial resolution is 2 km. There are three channels in the grating spectrometer. The 0.758 - 0.778 μm channel is used to detect O2-A, and its spectral resolution is 0.04 nm. The 1.594 - 1.624 μm channel is used to detect the weak CO2 band, and its spectral resolution is 0.08 nm. The 2.04 - 2.08 μm channel is used to detect the strong CO2 band, and its spectral resolution is 0.08 nm. However, it is difficult to quantitatively distinguish anthropogenic carbon emission sources from natural carbon emission sources by only observing a single CO2 element. Therefore, wide-area, high-efficiency, and multi-gas collaborative detection is the development trend of carbon monitoring satellites. The second type of solution takes GF-5 as an example. It realizes wide-swath and multi-type greenhouse gas detection. The GMI-II payload it carries uses spatial heterodyne spectroscopy (SHS) to obtain remote sensing data in the near-infrared to short-wave infrared (759 - 2058 nm) spectral range. Its spatial resolution is 10.5 km. GMI has 4 channels in its spectral range. The 0.759 - 0.769 μm channel is used to detect O2, and the spectral resolution of the first band is 0.6 cm -1 -1, the 1568 - 1583 nm channel is used to detect the weak CO2 band, the 1642 - 1658 nm channel is used to detect CH4, and the 2043 - 2058 nm channel is used to detect the strong CO2 band. The spectral resolution of these three channels is 0.27 cm -1 .

[0004] Although the above-mentioned technical solutions of greenhouse gas detection imaging spectrometers have all achieved high-index greenhouse gas detection, it is difficult to quantitatively distinguish anthropogenic carbon emission sources from natural carbon emission sources by only observing a single CO2 element. Summary of the Invention

[0005] The present invention aims to solve the technical problems in the prior art and provides an optical system for a large relative aperture, multi-channel, wide-width greenhouse gas detection spectrometer. The optical system of the present invention integrates the detection characteristics of large relative aperture, wide width, high spatial resolution, and multi-gas channels, can simultaneously monitor multiple gases with the same origin as anthropogenic carbon emissions, achieve collaborative observation, and thus accurately calculate the anthropogenic activity carbon emission sources.

[0006] To solve the above technical problems, the technical solution of the present invention is as follows:

[0007] An optical system for a large relative aperture, multi-channel, wide-width greenhouse gas detection spectrometer, comprising: a front-end telescopic system, a collimating lens group, and a rear-end five-channel system;

[0008] The front-end telescopic system has an off-axis two-mirror structure;

[0009] The collimating lens group is a focusing refractive lens group with a slit as the focus, and is used to achieve collimation in the wide wavelength band of 0.405 - 2.385 μm;

[0010] For the first channel, the second channel, the third channel, the fourth channel, and the fifth channel of the rear-end five-channel system, a beam splitter is used to achieve the pupil matching of the wide-width, large relative aperture splicing system; the dispersion element of each channel is a transmission grating, and the focusing lens group of each channel has an off-axis two-mirror structure;

[0011] The first channel is used to detect the gas NO2;

[0012] The second channel is used to detect the gas O2;

[0013] The third channel is used to detect the gases CO2 and CH4;

[0014] The fourth channel is used to detect the gas CO2;

[0015] The fifth channel is used to detect the gases CO and CH4;

[0016] The beam splitter is a prism beam splitting system formed by splicing right-angle prism groups;

[0017] The solar radiation passing through the atmosphere, after being absorbed by greenhouse gas molecules and diffusely reflected by the ground, passes through the atmosphere again and reaches the spectrometer optical system. Then, the front-end telescopic system images it at the slit, forms a focused image at the slit. The light passing through the slit is collimated by the collimating lens group and enters the prism beam splitting system, and the beam splitting and spatial layout of each narrow channel are completed in combination with narrow-band filters. Then, spectral splitting is realized by the transmission gratings of each channel, and finally, the absorption characteristic spectra of atmospheric molecules are formed on the detectors of each channel. In the above technical solution, the spatial layout of the optical system is arranged in a windmill shape.

[0018] In the above technical solution, the collimating lens group is composed of 4 lenses and two doublet lenses.

[0019] In the above technical solution, each channel of the rear-end five-channel includes a transmission grating, a focusing lens group and a detector, wherein the focusing lens group is an off-axis two-reflection structure.

[0020] In the above technical solution, the wavelength band of the transmission grating of the first channel is 405 - 490 nm, the wavelength band of the transmission grating of the second channel is 747 - 773 nm, the wavelength band of the transmission grating of the third channel is 1590 - 1675 nm, the wavelength band of the transmission grating of the fourth channel is 1990 - 2095 nm, and the wavelength band of the transmission grating of the fifth channel is 2325 - 2385 nm.

[0021] In the above technical solution, the off-axis two-reflection structure includes a primary off-axis reflector and a secondary off-axis reflector.

[0022] In the off-axis two-reflection structure of the front-end telescopic system in the above technical solution, the surface of the primary off-axis reflector is a free-form surface with a radius of curvature of 163.049 mm, and the surface of the secondary off-axis reflector is a quadratic surface with a radius of curvature of 291.971 mm.

[0023] The beneficial effects of the present invention are:

[0024] The optical system of the large relative aperture multi-channel wide-width greenhouse gas detection spectrometer of the present invention has the following advantages:

[0025] 1. The optical system of the present invention can simultaneously monitor multiple gases homologous to anthropogenic carbon emissions, realize collaborative observation, and thus accurately calculate anthropogenic activity carbon emission sources.

[0026] 2. The present invention takes a width of 170 km as the design index, realizes wide-area detection while ensuring high-spectral detection. The off-axis two-reflection structure is selected as the front-end telescopic system to realize large-field-of-view detection, and the reflective structure can avoid chromatic aberration caused by simultaneous detection of multiple gas bands.

[0027] 3. In the case of the common Offner as the spectroscopic structure, the present invention selects a transmission grating to complete the spectroscopy of 5 channels, and designs a transmission lens group based on the achromatic theory to complete the collimation of light rays. The present invention replaces the convex grating with a transmission grating, reduces the alignment difficulty and increases the stability.

[0028] 4. The five imaging lens groups of the five channels select the off-axis two-reflection structure, and a prism dichroic system is designed to complete the spatial layout of the five channels. Finally, after overall splicing, the horizontal and vertical dimensions of the system are similar, the structure is compact, the integration degree is high, and it is more conducive to use in the field of spaceborne remote sensing detection.

[0029] 5. The design with a large relative aperture improves the utilization efficiency of light energy. The entire gas band distribution ranges from visible to near-infrared, obtaining richer target spectral information and enhancing the comprehensiveness of gas detection. Description of the Drawings

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

[0031] Figure 1 It is a schematic structural diagram of the optical system of the large relative aperture multi-channel wide-width greenhouse gas detection spectrometer of the present invention.

[0032] Figure 2 It is a three-dimensional view of the optical system of the large relative aperture multi-channel wide-width greenhouse gas detection spectrometer of the present invention.

[0033] Figure 3 It is a schematic diagram of the prism beam splitting system of the present invention.

[0034] Figure 4 It is a schematic structural diagram of the prism beam splitting system of the present invention.

[0035] Figure 5 It is the MTF graph of the 0.405 - 0.490 μm channel.

[0036] Figure 6 It is the MTF graph of the 0.747 - 0.773 μm channel.

[0037] Figure 7 It is the MTF graph of the 1.590 - 1.675 μm channel.

[0038] Figure 8 It is the MTF graph of the 1.990 - 2.095 μm channel.

[0039] Figure 9 It is the MTF graph of the 2.325 - 2.385 μm channel.

[0040] Figure 10 It is the spot diagram of the 0.40555 - 0.40665 μm channel.

[0041] Figure 11 It is the spot diagram of the 0.747 - 0.74722 μm channel.

[0042] Figure 12 It is the spot diagram of the 1.63227 - 1.63273 μm channel.

[0043] Figure 13 It is the spot diagram of the 2.0422 - 2.0428 μm channel.

[0044] Figure 14 It is the spot diagram of the 2.35475 - 2.35525 μm channel.

[0045] The reference numerals in the figures are shown as follows:

[0046] 41 - Primary off-axis reflector of the front-end telescopic system, 42 - Secondary off-axis reflector of the front-end telescopic system, 43 - Refractive lens group, 44 - Prism beam splitting system, 45 - Secondary off-axis reflector of the first-channel focusing lens group, 46 - Primary off-axis reflector of the first-channel focusing lens group, 47 - Secondary off-axis reflector of the second-channel focusing lens group, 48 - Primary off-axis reflector of the second-channel focusing lens group, 49 - Secondary off-axis reflector of the third-channel focusing lens group, 50 - Primary off-axis reflector of the third-channel focusing lens group, 51 - Secondary off-axis reflector of the fourth-channel focusing lens group, 52 - Primary off-axis reflector of the fourth-channel focusing lens group, 53 - Secondary off-axis reflector of the fifth-channel focusing lens group, 54 - Primary off-axis reflector of the fifth-channel focusing lens group. Detailed implementation mode

[0047] The inventive concept of the present invention is as follows: The present invention proposes a design scheme for a large relative aperture multi-channel wide-field greenhouse gas detection imaging spectrometer. First, gases CO, CH4, and NO2, which are homologous to anthropogenic CO2 emissions, are determined to achieve multi-gas collaborative detection, thereby accurately measuring anthropogenic carbon emissions. Then, according to the detection band requirements, the band ranges of each channel are determined, and according to the index requirements, an optical system design scheme with a wide spectral band, a large relative aperture, and a large field of view is proposed. The design scheme is as Figure 1 shown. The overall optical system of the spectrometer is divided into three parts. The front-end telescopic system is an off-axis two-mirror structure. The collimating system consists of 4 lenses and two doublets. Based on the achromatic theory, materials are selected to achieve collimation in the wide band of 0.405 - 2.385 μm. The dispersion elements of the five channels at the back end are all transmission gratings. The prism beam splitter is used to solve the problem of difficult pupil matching in the wide-field and large relative aperture splicing system. Finally, the overall spatial layout is in the shape of a "windmill". Each channel of the focusing system is an off-axis two-mirror structure, and the overall spatial layout is relatively compact. The optical system of the present invention combines the detection characteristics of a large relative aperture, a wide field of view, a high spatial resolution, and multi-gas channels. Among them, the large relative aperture meets the requirements of high-precision detection, the wide field of view meets the requirements of wide-area detection, realizes large-area observation, improves the regional scale of carbon dioxide distribution monitoring, the high spatial resolution and multi-gas channel detection improve the accuracy of the detection results. The high spatial resolution can also accurately locate the emission sources, monitor the concentration changes and distribution differences of greenhouse gases in a small area. The multi-gas channel detection enables the system to have the ability to detect multiple greenhouse gases simultaneously. By collaborating with the gases homologous to anthropogenic carbon emissions, not only can the carbon dioxide concentration be accurately inverted, but also the anthropogenic carbon emission sources of carbon dioxide can be inferred according to the proportion of its homologous gases.

[0048] The present invention will be described in detail below with reference to the accompanying drawings.

[0049] Combined withFigure 1 and 2 Specifically describe the optical system of the large relative aperture multi-channel wide-width greenhouse gas detection spectrometer of the present invention, which includes a front-end telescopic system, a collimating mirror group, and a rear-end five-channel part; among them, the front-end telescopic system is an off-axis two-reflector structure, including the main off-axis reflector 41 and the secondary off-axis reflector 42 of the front-end telescopic system. The collimating mirror group is a focusing refractive lens group 43 with a slit as the focus. The refractive lens group 43 is composed of 4 lenses and two doublet lenses. As the co-collimation system of the spectrometer, materials are selected based on the achromatic theory to achieve collimation in the wide wavelength band of 0.405 - 2.385μm. The first channel, the second channel, the third channel, the fourth channel, and the fifth channel of the rear-end five-channel use a beam splitter to achieve the pupil matching of the wide-width and large relative aperture splicing system. Finally, the overall spatial layout of the optical system of the present invention is in the shape of a "windmill"; the dispersion element of each channel is a transmission grating, and the focusing mirror group of each channel is an off-axis two-reflector structure; each channel includes a dispersion element transmission grating, a focusing mirror group, and a detector, where the focusing mirror group is an off-axis two-reflector structure; the beam splitter is a prism beam splitting system 44 spliced by a right-angle prism group. The wavelength band of the transmission grating of the first channel is 405 - 490nm; the focusing mirror group of the first channel includes the main off-axis reflector 46 and the secondary off-axis reflector 45 of the first-channel focusing mirror group. As the spectroscopic system of the first channel, the main gas detected by this channel is NO2. The wavelength band of the transmission grating of the second channel is 747 - 773nm; the focusing mirror group of the second channel includes the main off-axis reflector 48 and the secondary off-axis reflector 47 of the second-channel focusing mirror group. As the spectroscopic system of the second channel, the main gas detected by this channel is O2. The wavelength band of the transmission grating of the third channel is 1590 - 1675nm; the focusing mirror group of the third channel includes the main off-axis reflector 50 and the secondary off-axis reflector 49 of the third-channel focusing mirror group. As the spectroscopic system of the third channel, the main gases detected by this channel are CO2 and CH4. The wavelength band of the transmission grating of the fourth channel is 1990 - 2095nm; the focusing mirror group of the fourth channel includes the main off-axis reflector 52 and the secondary off-axis reflector 51 of the fourth-channel focusing mirror group. As the spectroscopic system of the fourth channel, the main gas detected by this channel is CO2. The wavelength band of the transmission grating of the fifth channel is 2325 - 2385nm; the focusing mirror group of the fifth channel includes the main off-axis reflector 54 and the secondary off-axis reflector 53 of the fifth-channel focusing mirror group. As the spectroscopic system of the fifth channel, the main gases detected by this channel are CO and CH4.

[0050] In the optical system of the large relative aperture multi-channel wide-width greenhouse gas detection spectrometer of the present invention, after the solar radiation passing through the atmosphere is absorbed by greenhouse gas molecules and diffusely reflected by the ground, it passes through the atmosphere again and reaches the optical system of the spectrometer. Then, the front telescopic system images it at the slit, focuses and images at the slit. The light passing through the slit is collimated by the collimating mirror group and then enters the prism beam splitting system 44, and the beam splitting and spatial layout of each narrow channel are completed in combination with the narrowband filter. Then, the transmission gratings of each channel are used for spectral splitting respectively, and finally, the absorption characteristic spectral lines of atmospheric molecules are formed on the detectors of each channel.

[0051] The parameters of the optical structure of the imaging module (i.e., the front telescopic system) are as follows:

[0052]

[0053] The parameters of the transmission gratings of each channel are as follows:

[0054]

[0055] In the optical system of the large relative aperture multi-channel wide-width greenhouse gas detection spectrometer of the present invention, for the principle and design of the prism beam splitting system 44, please refer to Figure 3 and Figure 4 .

[0056] According to the beam diameter and the exit pupil position of the front telescopic system, a right-angle prism group is designed to ensure that the light beams of all channels can pass through completely. The schematic diagram is shown in Figure 3 . As shown in Figure 4 , the right-angle prism group is spliced into the prism beam splitting system 44. The reflection band of the thin film deposited on the reflection surface a is 747 - 1675 nm, and the reflection band of the thin film deposited on the reflection surface b is 1990 - 2385 nm. After the incident light is split by the prism group, the light of the first channel is transmitted along the positive direction of the Z axis, and the light of the second and third channels is reflected along the negative direction of the Y axis, and the light of the fourth and fifth channels is reflected along the positive direction of the Y axis. The reflection band of the thin film deposited on the reflection surface c is 747 - 773 nm, the reflection band of the thin film deposited on the reflection surface d is 1590 - 1675 nm, and the reflection band of the thin film deposited on the reflection surface e is 1990 - 2095 nm. After the light of the second and third channels passes through the reflection surfaces c and d, the light of the second channel is reflected along the positive direction of the z axis, and the light of the third band is reflected along the negative direction of the z axis. After the light of the fourth and fifth channels passes through the reflection surface e, the light of the fourth channel is reflected along the negative direction of the z axis, and the light of the fifth band is transmitted along the positive direction of the Y axis. The beam splitting and spatial arrangement of the five channels are completed, and the problem of difficult splicing caused by the increase in the optical path distance with the increase in the number of channels is solved.

[0057] The optical system of the large relative aperture multi-channel wide-width greenhouse gas detection spectrometer of the present invention has been verified by simulation with optical design related software. The F-number of each channel is 1.5 - 2.5, the field of view is 14°, the pixel size after merging is 60μm, the ground resolution of each channel is 198m - 290m, and the optical transfer function MTF is greater than 0.7 at the Nyquist frequency of 10 l p / mm, and gases such as CO2, CH4, CO, and NO2 can be detected. Figures 5 - 9 is the mtf of the central wavelength of each channel of the system, Figures 10 - 14 is the spot diagram of the splitting points of adjacent single wavelengths in each channel.

[0058] In summary, the present invention combines a large relative aperture, a large field of view, and a high spatial resolution, designs a wide-area high-precision multi-channel greenhouse gas detection spectrometer, uses a reflective structure and an achromatic theory to complete the detection design across a wide wavelength band, and designs a prism beam splitting group to complete the system integration. The optical system of the present invention combines the detection characteristics of a large relative aperture, a wide width, a high spatial resolution, and multiple gas channels. By co-detecting with gases homologous to anthropogenic carbon emissions, the present invention can not only accurately invert the carbon dioxide concentration but also infer the anthropogenic carbon emission sources of carbon dioxide based on the proportion of its homologous gases.

[0059] Obviously, the above embodiments are only examples for clear illustration and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation manners here. The obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A large relative aperture multi-channel wide-band greenhouse gas detection spectrometer optical system, characterized in that: include: Front telescope system, collimator lens group and rear five channels; The front telescopic system is an off-axis dual-mirror structure; The collimator lens group is a focusing refracting lens group with the slit as the focus, which is used to achieve collimation in a wide band of 0.405-2.385 μm; The first channel, the second channel, the third channel, the fourth channel and the fifth channel of the five rear channels use beam splitters to achieve pupil matching of a splicing system with a wide width and a large relative aperture; the dispersion element of each channel is a transmission grating, and the focusing lens group of each channel is an off-axis two-mirror structure; The first channel is used to detect gas NO2; The second channel is used to detect gas O2; The third channel is used to detect gases CO2 and CH4; The fourth channel is used to detect gas CO2; The fifth channel is used to detect gases CO and CH4; The beam splitter is a prism beam splitting system formed by splicing a right-angle prism group; After being absorbed by greenhouse gas molecules and diffusely reflected by the ground, solar radiation that passes through the atmosphere passes through the atmosphere again to reach the spectrometer optical system. The front telescope system then images it at the slit, focuses it at the slit, and the light that passes through the slit is collimated by the collimating lens group and then enters the prism beam splitting system. The beam splitting and spatial layout of each narrow channel are completed in combination with a narrow-band filter. The transmission grating of each channel then realizes beam splitting, and finally forms the absorption characteristic spectral lines of the atmospheric molecules on the detectors of each channel.

2. The optical system of the large relative aperture multi-channel wide-band greenhouse gas detection spectrometer according to claim 1, characterized in that: The spatial layout of the optical system is arranged in a windmill shape.

3. The large relative aperture multi-channel wide-band greenhouse gas detection spectrometer optical system according to claim 1, characterized in that: The collimating lens group is composed of four lenses and two double-cemented lenses.

4. The optical system of the large relative aperture multi-channel wide-band greenhouse gas detection spectrometer according to claim 1, characterized in that: Each of the five rear channels comprises a transmission grating, a focusing lens group and a detector, wherein the focusing lens group is an off-axis two-reflection structure.

5. The optical system of the large relative aperture multi-channel wide-band greenhouse gas detection spectrometer according to claim 4, characterized in that: The wavelength band of the transmission grating of the first channel is 405-490nm, the wavelength band of the transmission grating of the second channel is 747-773nm, the wavelength band of the transmission grating of the third channel is 1590-1675nm, the wavelength band of the transmission grating of the fourth channel is 1990-2095nm, and the wavelength band of the transmission grating of the fifth channel is 2325-2385nm.

6. The large relative aperture multi-channel wide-band greenhouse gas detection spectrometer optical system according to claim 1, characterized in that: The off-axis two-mirror structure comprises a primary off-axis reflector and a secondary off-axis reflector.

7. The optical system of the large relative aperture multi-channel wide-band greenhouse gas detection spectrometer according to claim 6, characterized in that: In the off-axis dual-reflector structure of the front-end telescope system, the surface of the primary off-axis reflector is a free-form surface with a curvature radius of 163.049 mm, and the surface of the secondary off-axis reflector is a quadratic surface with a curvature radius of 291.971 mm.

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