A space-borne solar-induced chlorophyll fluorescence spectral detection imaging system

Abstract

The application discloses a kind of spaceborne sunlight-induced chlorophyll fluorescence spectrum detection imaging systems, belong to spectral imaging technical field.The system includes telescope optical system, field separator component, hyperspectral spectrometer system and hyperspectral spectrometer system.The vegetation chlorophyll signal from ground is concentrated after telescope optical system, and is separated into first field and second field object signal by field separator component, and chlorophyll fluorescence information and vegetation photochemical index information are synchronously acquired by hyperspectral spectrometer system and hyperspectral spectrometer system respectively.The present application realizes the synchronous high-precision detection of chlorophyll fluorescence and vegetation physiological parameters, supports dynamic spectral sampling matching fluorescence peak and valley characteristics, and provides advanced remote sensing technical means for global vegetation photosynthesis and carbon cycle research.

Description

Technical Field

[0001] This invention belongs to the field of spectral imaging technology, specifically relating to a spaceborne solar-induced chlorophyll fluorescence spectral detection and imaging system. Background Technology

[0002] Chlorophyll fluorescence is a natural probe of plant photosynthesis, directly reflecting the photosynthetic efficiency and physiological state of vegetation. Remote sensing of sun-induced chlorophyll fluorescence (SIF) provides an important tool for global carbon cycle monitoring, vegetation stress monitoring, and primary productivity estimation. However, due to the extremely weak SIF signal (typically only 1%-5% of the reflected signal) and its susceptibility to interference from atmospheric scattering and aerosol polarization effects, high-precision spaceborne detection faces significant challenges.

[0003] Currently, chlorophyll fluorescence detection mainly relies on ground-based instruments (such as hyperspectral analyzers and portable measuring devices), making it difficult to achieve large-scale, continuous observation. While existing spaceborne sensors (such as ESA's FLEX-FLORIS and NASA's OCO-2) can also detect chlorophyll fluorescence (SIF), they still have the following limitations:

[0004] Insufficient spectral resolution: Traditional hyperspectral loading (such as 3-5 nm resolution) cannot accurately capture the fluorescence peak and valley characteristics of the Franhofer line region (such as O2-A 760 nm, O2-B 687 nm), resulting in inversion errors.

[0005] Poor spatiotemporal matching: Fluorescence and vegetation photochemical indices (such as PRI) need to be observed simultaneously to correct for the influence of apparent reflectance, but existing systems mostly use time-sharing or field-of-view detection, resulting in insufficient data coordination.

[0006] Significant polarization interference: Aerosols exhibit wavelength-dependent polarization in the 400-850nm band (with a polarization degree of up to 58.6%), while conventional optical systems have high polarization sensitivity (>1%), leading to radiometric calibration errors.

[0007] The system is bulky: To achieve ultra-high spectral resolution (such as 0.05nm), traditional solutions require complex optical path designs. Even with the use of AHSI wide-swath wide-spectrum hyperspectral camera dual telecentric spectrometer technology, the spectrometer size still cannot meet the miniaturization requirements of spaceborne payloads.

[0008] To address the aforementioned issues, there is an urgent need to develop a spaceborne detection system that combines ultra-high spectral resolution (<0.3nm), wide swath coverage (>150km), and low polarization sensitivity (<0.5%). Through coordinated hyperspectral and hyperspectral observations, this system can achieve precise and synchronous inversion of chlorophyll fluorescence and vegetation physiological parameters, providing next-generation technical support for ecological remote sensing. Summary of the Invention

[0009] To address the aforementioned technical problems, this invention provides a spaceborne solar-induced chlorophyll fluorescence spectroscopy detection and imaging system. By combining hyperspectral and superspectral observation methods, it reduces the size of the hyperspectral instrument system to less than half that of the traditional system while meeting the requirements of high spectral resolution, high spatial resolution, large field of view, and low spectral distortion. This achieves the miniaturization, lightweighting, and integration of the spaceborne solar-induced chlorophyll fluorescence spectroscopy detection and imaging system.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] A spaceborne solar-induced chlorophyll fluorescence spectroscopy detection and imaging system includes a telescope optical system, a field-of-view splitter assembly, a hyperspectral spectrometer system, and a high-spectral spectrometer system, wherein...

[0012] After the chlorophyll signal from the ground is focused by the telescope optical system, the chlorophyll signal is divided into a first field-of-view object signal and a second field-of-view object signal by the field-of-view splitter component. The first field-of-view object signal is used to obtain chlorophyll fluorescence information by the hyperspectral spectrometer system, and the second field-of-view object signal is used to obtain photochemical index information of the vegetation by the hyperspectral spectrometer system.

[0013] The image-side numerical aperture of the telescope optical system is equal to the object-side numerical aperture of the hyperspectral spectrometer system and the hyperspectral spectrometer system, and the three systems share a common field of view across the track.

[0014] Furthermore, the telescope's optical system is an image-side telecentric structure, with a working wavelength of 500-780nm, a field of view of 30°, a focal length of 189.5mm, an F-number of 2.0-2.5, and an image-side telecentricity deviation of less than 2.5 degrees for the principal ray.

[0015] Furthermore, the field-of-view separator component is a roof reflector, with two reflecting surfaces being a hyperspectral field-of-view separator mirror and a hyperspectral field-of-view separator mirror, respectively. The vegetation chlorophyll signal is separated into a first field-of-view object signal by the hyperspectral field-of-view separator mirror and then enters the hyperspectral instrument system through the first slit. After being separated into a second field-of-view object signal by the hyperspectral field-of-view separator mirror, it enters the hyperspectral instrument system through the second slit.

[0016] Furthermore, both the first slit and the second slit are field stops with a length of 100mm.

[0017] Furthermore, the hyperspectral spectrometer system includes a first slit protection plate, a plane conversion mirror, a first meniscus correction lens, a third reflecting mirror, a grating, and a hyperspectral detector; the first field-of-view object signal is reflected to the grating after passing through the first slit protection plate, the plane conversion mirror, the first meniscus correction lens, and the third reflecting mirror in sequence; after being finely dispersed by the grating, the light is focused onto the hyperspectral detector again by the third reflecting mirror and the first meniscus correction lens; wherein, the first meniscus correction lens and the grating are coaxial; the first slit protection plate is tilted by 1~2° to further reduce the polarization degree of the hyperspectral system.

[0018] Furthermore, the hyperspectral spectrometer system has a spectral range of 665-780nm, and the hyperspectral detector uses pixels of size 80μm×40μm. The spectral sampling interval can be adjusted by controlling the sub-pixel splitting or merging output mode of the hyperspectral detector pixel, with an adjustment range of 0.06-0.24nm.

[0019] Furthermore, a narrow-band linear gradient filter is integrated on the surface of the hyperspectral detector, and its single-channel spectral spread width and initial and final wavelengths correspond one-to-one with the spread width and initial and final wavelengths of each spectral channel after fine spectral dispersion by the hyperspectral instrument system.

[0020] Furthermore, the hyperspectral spectrometer system includes a second slit protector, a second meniscus correction lens, a first reflecting mirror, a convex grating, a second reflecting mirror, a spectrometer plane-turning mirror, and a hyperspectral detector. The second field-of-view object signal is reflected and converged to the convex grating after passing through the second slit protector, the second meniscus correction lens, and the first reflecting mirror. After being finely dispersed by the convex grating, the signal sequentially reaches the second reflecting mirror and the second meniscus correction lens for further convergence, and is reflected to the hyperspectral detector by the spectrometer plane-turning mirror. The second slit protector is tilted by 1 to 2 degrees to further reduce the polarization degree of the hyperspectral system.

[0021] Furthermore, the hyperspectral spectrometer system has a spectral range of 500-680 nm and a spectral sampling interval of 2-4 nm.

[0022] Furthermore, each component of the telescope optical system, field separator assembly, hyperspectral spectrometer system, and hyperspectral spectrometer system is coated with an antipolarization film.

[0023] The beneficial effects of this invention are as follows:

[0024] This invention employs both hyperspectral and superspectral spectrometer systems to simultaneously observe spectra within the 500-650 nm range. Through accurate PRI and SIF information, it can precisely acquire information such as vegetation reflectance, chlorophyll content, leaf area index, vegetation index, and vegetation cover. This enables simultaneous observation of several key parameters in vegetation remote sensing, helps decouple the complex nonlinear relationship between fluorescence and photosynthesis, and can more effectively support applications such as total primary productivity inversion, monitoring of chlorophyll fluorescence's impact on environmental stress, and monitoring of surface biomass, aquatic environment, and soil organic matter.

[0025] This invention achieves adjustable spectral sampling interval by controlling the output mode of detector pixel sub-pixel splitting or merging, which solves the problem that the traditional mode with a single fixed spectral resolution cannot meet the technical requirements of fluorescence detection. It is particularly necessary to realize the adjustable spectral sampling interval and signal energy level matching function through on-orbit programming. For the fluorescence detection requirements, through energy level matching design, the signal-to-noise ratio can be improved by more than 50% at the weak signal valleys of the two oxygen absorption bands O2-B (F687) and O2-A (F760).

[0026] This invention employs a narrow-band linear gradient filter combined with a grating linear fine spectrophotometer system to achieve more precise spectral filtering, thereby enabling more effective stray light suppression measures that can improve the stray light suppression ratio by 300 times and achieve a stray light suppression ratio on the order of 10⁻⁹.

[0027] This invention coats each optical element with an anti-polarization film on its optical mirror surface, resulting in a linear polarization sensitivity better than 0.5%. The anti-polarization film enables high-efficiency energy transfer, accurate spectral resolution, and additional polarization suppression of the system, allowing S-polarized light and P-polarized light to complement each other in intensity and controlling the phase difference between S-polarized light and P-polarized light, thus enabling the linear polarization sensitivity LPS of the entire optical system to reach a high level of control.

[0028] Compared with traditional hyperspectral detection systems, this invention improves spectral resolution by more than 10 times, while taking into account the requirements of large field of view, high spatial resolution, and low spectral distortion. It also reduces the size by nearly half compared with traditional hyperspectral design schemes, significantly reducing the development and launch costs of satellite detection payloads. This invention achieves the miniaturization, weight reduction, and integration of a spaceborne solar-induced chlorophyll fluorescence spectral detection and imaging system. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of a spaceborne solar-induced chlorophyll fluorescence spectroscopy detection and imaging system according to the present invention;

[0030] Figure 2 This is a schematic diagram of the telescope optical system of the present invention;

[0031] Figure 3a This is a schematic diagram of the optical path of the light separated by the field separator of the present invention entering the hyperspectral spectrometer system;

[0032] Figure 3b This is a schematic diagram of the optical path of the light separated by the field-of-view separator of the present invention entering the hyperspectral spectrometer system;

[0033] Figure 4a This is a schematic diagram of the hyperspectral spectrometer system of the present invention;

[0034] Figure 4b This is a comparison chart showing the significant reduction in volume envelope of the hyperspectral spectrometer system of this invention compared to the traditional improved Offner structure;

[0035] Figure 5 This is the optical path diagram of the hyperspectral spectrometer system of the present invention;

[0036] Figure 6a A schematic diagram of the diffuse spot image quality at a wavelength of 0.677 μm in the hyperspectral spectrometer system of this invention;

[0037] Figure 6b A schematic diagram of the diffuse spot image quality at a wavelength of 0.7 μm for the hyperspectral spectrometer system of this invention;

[0038] Figure 6c A schematic diagram of the diffuse spot image quality designed at a wavelength of 0.775 μm for the hyperspectral spectrometer system of this invention;

[0039] Figure 7a A schematic diagram of the diffuse spot image quality at a wavelength of 0.5 μm in the hyperspectral spectrometer system of this invention;

[0040] Figure 7b A schematic diagram of the diffuse spot image quality at a wavelength of 0.59 μm for the hyperspectral spectrometer system of this invention;

[0041] Figure 7c A schematic diagram of the diffuse spot image quality at a wavelength of 0.68 μm for the hyperspectral spectrometer system of this invention;

[0042] Figure 8 This is a schematic diagram illustrating the application of the linear gradient filter of the present invention;

[0043] Figure 9 This is a schematic diagram of stray light suppression according to the present invention;

[0044] Figure 10 Program the radiance comparison chart before the spectral sampling interval;

[0045] Figure 11 A comparison chart of radiance after programming the spectral sampling interval;

[0046] Figure 12A schematic diagram for controlling the output mode of detector pixel sub-pixel splitting or merging, where (a)-(d) represent sampling intervals of 0.2, 0.3, 0.4, and 0.1 nm, respectively.

[0047] Figure label:

[0048] 1-1-Primary mirror of the telescope, 1-2-Secondary mirror of the telescope, 1-3-Third mirror of the telescope, 1-4-Image plane;

[0049] 2-1-Hyperspectral field separator mirror, 2-2-Hyperspectral field separator mirror, 5-1-First slit, 5-2-Second slit;

[0050] 3-1-First slit protection plate, 3-2-Plane conversion mirror, 3-3-First meniscus correction lens, 3-4-Third reflecting mirror, 3-5-Grate, 3-6-Hyperspectral detector;

[0051] 4-1-Second slit protection plate, 4-2-Second meniscus correction lens, 4-3-First reflecting mirror, 4-4-Convex grating, 4-5-Second reflecting mirror, 4-6-Spectrometer plane conversion mirror, 4-7-Hyperspectral detector. Detailed Implementation

[0052] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0053] like Figure 1 The present invention, as shown, is a spaceborne solar-induced chlorophyll fluorescence spectral detection and imaging system, including a telescope optical system, a field-of-view splitter assembly, a hyperspectral spectrometer system, and a superspectral spectrometer system.

[0054] The chlorophyll signal from the ground surface is focused by the telescope's optical system and then split into a first field-of-view object signal and a second field-of-view object signal by a field-of-view splitter component. The first field-of-view object signal is used to acquire chlorophyll fluorescence information by a hyperspectral spectrometer system, and the second field-of-view object signal is used to acquire photochemical index information of the vegetation by a hyperspectral spectrometer system. The telescope's optical system has an image-side telecentric structure, and its image-side numerical aperture must be equal to the object-side numerical aperture of the hyperspectral spectrometer system and the hyperspectral spectrometer system, while maintaining a cross-track common field of view to achieve imaging of the same area by the hyperspectral spectrometer system and the hyperspectral spectrometer system, so as to obtain perfectly matched chlorophyll fluorescence information and vegetation photochemical index information.

[0055] The optical system of this invention adopts an off-axis three-mirror design, which is unobstructed and has high optical efficiency, thus improving the spectral channel detection sensitivity of the hyperspectral imager. It also facilitates subsequent optomechanical assembly and system engineering implementation. The parameters of the optical system of this invention are shown in Table 1:

[0056] Table 1

[0057]

[0058] As a preferred embodiment, the optical system of the spaceborne wide-swath solar-induced chlorophyll fluorescence superluminescence detector imager of the present invention has a numerical aperture of 0.1-0.3, a spectral resolution of less than 0.3 nm, and a pixel size of 80 μm × 40 μm, which can be combined into a large pixel of 80 μm × 80 μm.

[0059] like Figure 2 The telescope optical system of the present invention shown is an off-axis three-mirror reflective optical system, including a primary mirror 1-1, a secondary mirror 1-2, and a third mirror 1-3.

[0060] The telescope optical system of the present invention differs from ordinary imaging objectives. In addition to meeting some basic requirements of general imaging objectives, it usually has the following characteristics.

[0061] (1) Wide spectral coverage. Imaging spectrometers are characterized by a wide operating band, typically requiring coverage of dozens or even hundreds of channels. This necessitates that the telescope's optical system be able to meet the requirements of wide spectral range imaging. A wide imaging spectral range has little impact on reflecting telescopes, but for refracting or catadioptric telescopes, the large chromatic aberration caused by the wide band needs to be considered, increasing the difficulty of system aberration correction.

[0062] (2) Numerical Aperture Coupling. To ensure high utilization of the spectrometer, the image-side numerical aperture of the telescope optical system must be equal to the object-side numerical apertures of the two spectrometers in the optical system, achieving perfect matching. If the numerical aperture of the telescope optical system is greater than or less than the numerical aperture of any one spectrometer, it will result in a waste of the imaging capability of the telescope optical system or the spectrometer. Due to the limitation of the imaging field of view by the slit, Earth observation spectrometers usually require a large relative aperture, i.e., a small F-number, in order to meet the signal-to-noise ratio requirements of the instrument. The visible light band usually has an F-number of less than 3.5, and the infrared band system requires an even smaller F-number, generally less than 2.5. This requires the telescope optical system to also be designed as a system with a small F-number to achieve perfect matching with the spectrometer and increase the light-gathering capability of the system.

[0063] (3) Image-side telecentric structure or near-image-side telecentric structure. An imaging spectrometer consists of a telescope optical system and a spectrometer connected by a pupil. Since the spectrometer is usually object-side telecentric, the telescope optical system should be image-side telecentric or near-image-side telecentric to match its pupil and achieve telecentricity matching. In an imaging spectrometer, the slit is the field stop. If the telescope optical system deviates from the image-side telecentric structure, the edge optics of the off-axis field of view cannot pass through the slit, resulting in vignetting, which in turn affects the signal-to-noise ratio of the instrument in that field of view. In order not to affect the imaging performance of the instrument, the vignetting caused by deviating from the image-side telecentric structure should be controlled within 10% or the principal ray deflection angle should be less than 2.5 degrees.

[0064] (4) The telescope optical system consists of a primary telescope 1-1, a secondary telescope 1-2, and a tertiary telescope 1-3. The surface parameters of the primary telescope 1-1 are: radius of curvature R: -6000mm, conic coefficient: -4.14, fourth-order aspheric coefficient: 7.59e-11, and sixth-order aspheric coefficient: -8.14e-17. The surface parameters of the secondary telescope 1-2 are: radius of curvature R: -404.98mm, conic coefficient: 3.326, fourth-order aspheric coefficient: -1.48e-9, and sixth-order aspheric coefficient: -7. .476e-14; The surface parameters of the three telescope mirrors 1-3 are: radius of curvature R: -423.07mm, conic coefficient: 0.157, fourth-order aspherical coefficient: -4.64e-11, sixth-order aspherical coefficient: -9.97e-16; The axial distance between the primary mirror 1-1 and the secondary mirror 1-2 corresponding to the mother mirror is -411.15mm; The axial distance between the secondary mirror 1-2 and the three telescope mirrors 1-3 corresponding to the mother mirror is 276.02mm; The distance from the three telescope mirrors 1-3 to the image plane 1-4 is -369.11mm.

[0065] Preferably, the telescope optical system of the present invention operates in the wavelength range of 500-780nm, has a field of view of 30°, a focal length of 189.5mm, and an F-number of 2.0-2.5; more preferably, the F-number is 2.2.

[0066] The field-of-view separator assembly of the present invention is a roof reflector device, including a hyperspectral field-of-view separator mirror 2-1 and a hyperspectral field-of-view separator mirror 2-2.

[0067] The chlorophyll fluorescence signal collected by the telescope's optical system is separated into the first field-of-view object signal by the hyperspectral field separator mirror 2-1, and then enters the hyperspectral instrument system through the first slit 5-1. Figure 3a As shown, after being separated into second field-of-view object signals by mirror 2-2 of the hyperspectral field separator, the signals enter the hyperspectral instrument system through the second slit 5-2. Figure 3b As shown.

[0068] Wherein, the first slit 5-1 and the second slit 5-2 are both field stops, located on both sides of the field separator, and their lengths are 100~110mm. More preferably, the lengths of the first slit 5-1 and the second slit 5-2 are both 100mm.

[0069] like Figure 4a The hyperspectral spectrometer system of the present invention, as shown, includes a first slit protection plate 3-1, a planar convoluted mirror 3-2, a first meniscus correction lens 3-3, a third reflecting mirror 3-4, a grating 3-5, and a hyperspectral detector 3-6. The first field-of-view object signal, separated by the field-of-view splitter mirror 2-1, passes through the first slit 5-1 and the first slit protection plate 3-1, is deflected by the planar convoluted mirror 3-2, transmitted through the first meniscus correction lens 3-3, and converged by the third reflecting mirror 3-4 to the grating 3-5. After fine dispersion by the grating, it is converged again by the third reflecting mirror 3-4 and then passes through the meniscus correction lens 3-3 to reach the hyperspectral detector 3-6. The first meniscus correction lens 3-3 and the grating 3-5 share the same optical axis. The first meniscus correction lens 3-3 achieves shared area reuse, and the third reflecting mirror 3-4 achieves shared use, reducing the volume of the hyperspectral detector by more than 59%. Figure 4b As shown, the first meniscus correction lens 3-3 is designed as a lens of equal thickness, which reduces the processing difficulty of the off-axis lens; the first slit protection plate 3-1 is tilted by 1~2° to further reduce the polarization degree of the hyperspectral system 3.

[0070] Traditional Offner spectrometers suffer from significant asymmetry. To ensure the dispersed beam isn't blocked by the grating, the slit's off-axis distance is substantial, resulting in a large aperture for the correction lens. This negatively impacts the spectrometer's stability and engineering feasibility, and adds unnecessary weight and volume. Therefore, this invention adjusts the traditional Offner spectrometer structure. The grating 3-5 and the first meniscus correction lens 3-3 are coaxial, allowing the beam, after fine dispersion by the grating 3-5, to pass through the same area of ​​the first meniscus correction lens 3-3 again, achieving a smaller, more compact design. Furthermore, this invention replaces the traditional hemispherical meniscus correction lens with a small meniscus prism and introduces a freeform surface into the third reflecting mirror 3-4, achieving a 300km field of view, a 0.1mm optical sampling interval, and a doubling of spectral subdivision capability. The hyperspectral spectrometer system 3 of this invention is a non-coaxial system (the third reflecting mirror 3-4 and the first meniscus correction lens 3-3 are not coaxial). This aims to improve the system's aberration-correction degree of freedom parameters, ensuring a significantly increased field of view and enhanced spectral subdivision capability while controlling spectral distortion within 0.3 pixels, spectral curvature less than 0.3 pixels, and spectrometer image quality RMS less than 0.5 pixels. The third reflecting mirror 3-4 of this invention is reused twice in the entire spaceborne wide-swath solar-induced chlorophyll fluorescence hyperspectral detection and imaging system. This simplifies the spectrometer's structural complexity, reduces its size, and lowers payload development and launch costs. It corrects spectral distortion (a type of aberration). In practice, using two mirrors would provide stronger distortion correction; this is only to simplify the optical system and reduce size. To reduce the development difficulty of the large blaze angle grating 3-5 and facilitate engineering development, the reflecting mirror 3-3 of this invention can be a grating surface.

[0071] Preferably, the hyperspectral spectrometer system of the present invention has a spectral range of 665-780 nm. To address the limitations of traditional modes with a single, fixed spectral resolution that cannot meet the requirements of fluorescence detection, adjustable spectral sampling intervals and signal energy level matching are implemented through on-orbit programming. The spectral sampling interval adjustment range is 0.06-0.24 nm. The adjustable spectral sampling interval function is achieved by controlling the output mode of detector pixel sub-pixel splitting or merging (e.g., ...). Figure 12 Where: (a)-(d) represent sampling intervals of 0.2, 0.3, 0.4, and 0.1 nm, respectively. The spectral sampling interval is 0.12 nm @ d = 40 μm. When using a pixel size of d = 20 μm, the corresponding spectral sampling interval is 0.06 nm @ d = 20 μm. When the two spectral dimensions are combined, the spectral sampling interval is 0.24 nm @ d = 80 μm. For fluorescence detection requirements, the adjustable spectral sampling interval enables matching of spectral sampling with the absorption peaks and valleys of the oxygen absorption band (e.g., ...). Figure 10 and Figure 11(As shown); through energy level matching design, the signal-to-noise ratio can be improved by more than 50% at the weak signal valleys of the two oxygen absorption bands O2-B (F687) and O2-A (F760).

[0072] The spectrometer has a compact structure. Preferably, the linear graded filter is located on the hyperspectral detector 3-6 and integrated with the detector. To better suppress stray light, the single-channel spectral spread width and initial and final wavelength of the linear graded filter of this invention correspond one-to-one with the spread width and initial and final wavelength of each spectral channel after fine dispersion by the hyperspectral spectrometer system, thereby improving the signal-to-noise ratio of the fine spectral channels. The diffuse spot size of the hyperspectral spectrometer system of this invention is as follows: Figures 6a-6c As shown.

[0073] This invention employs a linear graded filter combined with a linear spectrometer system to achieve more precise spectral channel filtering, such as... Figure 8 As shown, traditional stray light analysis methods have low light utilization rates, meaning most light rays cannot reach the energy threshold and disappear after scattering within the optomechanical system. Only a small portion of relatively obvious stray light paths can be detected through simulation, while the remaining weak stray light paths are difficult to detect through simulation. However, based on the higher precision and more efficient stray light suppression method of this invention, light rays will scatter in directions more favorable for entering the hyperspectral detector 3-6, making even weaker stray light paths easily detectable through simulation. Furthermore, the stray light paths detected by the higher precision and more efficient stray light analysis method can be further optimized by improving the internal structure of the telescope's hood, the second-order aperture of the optomechanical structure, and the positions of the Leo aperture and field aperture, resulting in a stray light suppression ratio that can be improved by 10 times.

[0074] Traditional stray light suppression methods can suppress most stray light energy, but they cannot suppress the second-order and multi-order scattering energy from the detector's front structure, such as... Figure 9 As shown, the hyperspectral camera differs from other cameras in that it precisely splits the light through gratings 3-5. Each column of its effective signal energy is a narrow bandpass energy. Therefore, the hyperspectral detector 3-6 of this invention is designed with a linearly graded filter. The filter area above each pixel of the detector column is a very narrow bandpass filter area. Broadband stray light passes through the linearly graded filter, and only light with a very narrow spectral bandwidth energy can pass through and be incident on the hyperspectral detector 3-6. By rationally designing the bandwidth of the linearly graded filter, the stray light suppression ratio can be improved by 30 times. Through simulation analysis, the more effective stray light suppression measures designed in this invention can improve the stray light suppression ratio by 300 times, achieving a stray light suppression ratio of 10. -9 Magnitude.

[0075] like Figure 5As shown, the hyperspectral spectrometer system of the present invention includes a second slit protection plate 4-1, a second meniscus correction lens 4-2, a first reflecting mirror 4-3, a convex grating 4-4, a second reflecting mirror 4-5, a spectrometer plane conversion mirror 4-6, and a hyperspectral detector 4-7. The second field-of-view object signal separated by the field-of-view separator mirror 2-2 passes through the second slit 5-2 and the second slit protection plate 4-1, is transmitted through the second meniscus correction lens 4-2, converged by the first reflecting mirror 4-3 to the convex grating 4-4, is finely dispersed by the convex grating 4-4, converged by the second reflecting mirror 4-5, passes again through the second meniscus correction lens 4-2, and is converted by the spectrometer conversion mirror 4-6 to reach the hyperspectral detector 4-7.

[0076] Preferably, the hyperspectral spectrometer system of the present invention has a spectral range of 500-680 nm and a spectral sampling interval of 2-4 nm, and more preferably, a spectral sampling interval of 3 nm.

[0077] Preferably, the dispersion spot size of the hyperspectral spectrometer system of the present invention is as follows: Figures 7a-7c As shown.

[0078] In practical applications, the chlorophyll fluorescence signal enters the telescope optical system and is focused by the telescope primary mirror 1-1, the telescope secondary mirror 1-2, and the telescope tertiary mirror 1-3 in sequence. Then, the chlorophyll fluorescence signal is divided into the first field-of-view object signal and the second field-of-view object signal by the field-of-view splitter assembly.

[0079] The first field object signal is focused onto the first slit 5-1 of the hyperspectral spectrometer system, and then passes sequentially through the first slit protection plate 3-1, the plane conversion mirror 3-2, and the first meniscus correction lens 3-3. It is then reflected and converged by the mirror 3-4 to the grating 3-5. After being finely dispersed by the grating 3-5, it passes again through the mirror 3-4 and the first meniscus correction lens 3-3 and is focused onto the hyperspectral detector 3-6.

[0080] The second field object signal is focused onto the second slit 5-2 of the hyperspectral spectrometer system, and then reflected by the first mirror 4-3 to the convex grating 4-4 ​​after passing through the second slit protection plate 4-1 and the second meniscus correction lens 4-2. After being finely dispersed by the grating, it is converged by the second mirror 4-5 and the second meniscus correction lens 4-2, and then deflected by the spectrometer deflector 4-6 onto the hyperspectral detector 4-7. The second slit protection plate 4-1 is tilted by 1~2° to further reduce the polarization degree of the hyperspectral system 4.

[0081] Furthermore, in the spaceborne wide-swath solar-induced chlorophyll fluorescence hyperspectral detection and imaging system of the present invention, each element of the system is coated with an anti-polarization film, resulting in a linear polarization sensitivity better than 0.5%. The anti-polarization film needs to play a functional role on each optical surface: high-efficiency energy transfer, accurate spectral realization, and additional polarization suppression of the system.

[0082] In optical systems, any oblique incidence will generate additional polarization, causing a distorted response from the instrument to the received optical information. To control this additional polarization (which can be quantified as linear polarization sensitivity LPS), system polarization control is required using optical thin films on each optical surface. Based on a comprehensive design, the polarization spectrum of individual elements is measured, and the design of thin film elements with severe polarization separation is adjusted to achieve complementarity in intensity between S-polarized and P-polarized light. By controlling the phase difference between S-polarized and P-polarized light, the linear polarization sensitivity LPS of the entire optical system can be achieved at a high level of control.

[0083] In summary, the present invention can achieve very low system polarization sensitivity through the following technical controls:

[0084] (1) Control the linear polarization sensitivity of key components (such as meniscus lenses). High transmittance is used to control the significant separation of S-polarized and P-polarized light, avoiding serious difficulties in system polarization control;

[0085] (2) Precise measurement of the linear polarization sensitivity of thin-film elements;

[0086] (3) Based on the polarization measurement results of a single element, the polarization spectrum and LPS values ​​of the optical system at different wavelengths and angles are obtained by combining the Jones matrix and the Mueller matrix for calculation and analysis, providing support for system testing and calibration.

[0087] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A spaceborne solar-induced chlorophyll fluorescence spectral detection and imaging system, characterized in that, This includes the telescope optical system, field-of-view splitter assembly, hyperspectral spectrometer system, and hyperspectral spectrometer system, among which... After the chlorophyll signal from the ground is focused by the telescope optical system, the chlorophyll signal is divided into a first field-of-view object signal and a second field-of-view object signal by the field-of-view splitter component. The first field-of-view object signal is used to obtain chlorophyll fluorescence information by the hyperspectral spectrometer system, and the second field-of-view object signal is used to obtain photochemical index information of the vegetation by the hyperspectral spectrometer system. The image-side numerical aperture of the telescope optical system is equal to the object-side numerical aperture of the hyperspectral spectrometer system and the hyperspectral spectrometer system, and the three systems share a common field of view across the track. The hyperspectral spectrometer system includes a first slit protection plate (3-1), a plane convoluted mirror (3-2), a first meniscus correction lens (3-3), a third reflecting mirror (3-4), a grating (3-5), and a hyperspectral detector (3-6). The first field-of-view object signal is reflected to the grating (3-5) after passing through the first slit protection plate (3-1), the plane convoluted mirror (3-2), the first meniscus correction lens (3-3), and the third reflecting mirror (3-4) in sequence. After being finely dispersed by the grating (3-5), the light is focused onto the hyperspectral detector (3-6) again by the third reflecting mirror (3-4) and the first meniscus correction lens (3-3). The first meniscus correction lens (3-3) and the grating (3-5) are coaxial. A narrow-band linear gradient filter is integrated on the surface of the hyperspectral detector (3-6), and the single-channel spectral spread width and initial and final wavelengths of the filter correspond one-to-one with the spread width and initial and final wavelengths of each spectral channel after fine dispersion by the hyperspectral spectrometer system. The hyperspectral spectrometer system includes a second slit protection plate (4-1), a second meniscus correction lens (4-2), a first reflector (4-3), a convex grating (4-4), a second reflector (4-5), a spectrometer plane conversion mirror (4-6), and a hyperspectral detector (4-7). The second field-of-view object signal is reflected and converged to the convex grating (4-4) after passing through the second slit protection plate (4-1), the second meniscus correction lens (4-2), and the first reflector (4-3). After being finely dispersed by the convex grating (4-4), the signal reaches the second reflector (4-5) and the second meniscus correction lens (4-2) again for convergence, and is reflected to the hyperspectral detector (4-7) by the spectrometer plane conversion mirror (4-6).

2. The spaceborne solar-induced chlorophyll fluorescence spectral detection and imaging system according to claim 1, characterized in that, The telescope's optical system is an image-side telecentric structure, with a working wavelength of 500-780nm, a field of view of 30°, a focal length of 189.5mm, an F-number of 2.0-2.5, and an image-side telecentricity deviation of less than 2.5 degrees for the principal ray.

3. The spaceborne solar-induced chlorophyll fluorescence spectral detection and imaging system according to claim 1, characterized in that, The field-of-view separator assembly is a roof reflector with two reflective surfaces, namely the hyperspectral field-of-view separator mirror (2-1) and the hyperspectral field-of-view separator mirror (2-2). The vegetation chlorophyll signal is separated into a first field-of-view object signal by the hyperspectral field-of-view separator mirror (2-1) and then enters the hyperspectral instrument system through the first slit (5-1). After being separated into a second field-of-view object signal by the hyperspectral field-of-view separator mirror (2-2), it enters the hyperspectral instrument system through the second slit (5-2).

4. The spaceborne solar-induced chlorophyll fluorescence spectral detection and imaging system according to claim 3, characterized in that, The first slit (5-1) and the second slit (5-2) are both field stops with a length of 100 mm.

5. The spaceborne solar-induced chlorophyll fluorescence spectral detection and imaging system according to claim 1, characterized in that, The hyperspectral spectrometer system has a spectral range of 665-780nm. The hyperspectral detector (3-6) uses 80μm×40μm pixels. The spectral sampling interval can be adjusted by controlling the sub-pixel splitting or merging output mode of the hyperspectral detector (3-6). The adjustment range is 0.06-0.24nm.

6. The spaceborne solar-induced chlorophyll fluorescence spectral detection and imaging system according to claim 1, characterized in that, The hyperspectral spectrometer system has a spectral range of 500-680 nm and a spectral sampling interval of 2-4 nm.

7. The spaceborne solar-induced chlorophyll fluorescence spectral detection and imaging system according to claim 1, characterized in that, Each component of the telescope optical system, field separator assembly, hyperspectral spectrometer system, and hyperspectral spectrometer system is coated with an antipolarization film.

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