Satellite-borne sunlight-induced chlorophyll fluorescence spectrum detection imaging system

Abstract

The invention discloses a satellite-borne sunlight-induced chlorophyll fluorescence spectrum detection imaging system, and belongs to the technical field of spectral imaging. The system includes a telescope optical system, a field-of-view separator assembly, a hyperspectral spectrometer system, and a hyperspectral spectrometer system. A vegetation chlorophyll signal from the earth surface is condensed by the telescope optical system and then is separated into a first view field object signal and a second view field object signal by the view field separator assembly, and chlorophyll fluorescence information and vegetation photochemical index information are synchronously acquired by the hyper-spectral spectrograph system and the hyperspectral spectrograph system respectively. According to the invention, synchronous high-precision detection of chlorophyll fluorescence and vegetation physiological parameters is realized, dynamic spectrum sampling is supported to match fluorescence peak valley characteristics, and an advanced remote sensing technical means is provided for global vegetation photosynthesis and carbon cycle research.

Description

Technical Field

[0001] The present invention belongs to the technical field of spectral imaging, and in particular relates to a satellite-borne sunlight-induced chlorophyll fluorescence spectral detection imaging system. Background Art

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

[0003] Currently, chlorophyll fluorescence detection relies primarily on ground-based instruments (such as hyperspectral analyzers and portable measurement equipment), which makes it difficult to achieve large-scale, continuous observations. Existing spaceborne sensors (such as ESA's FLEX-FLORIS and NASA's OCO-2) can also detect SIF, but they still have the following limitations:

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

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

[0006] Polarization interference is significant: Aerosols have wavelength-dependent polarization in the 400-850nm band (with a maximum polarization degree of 58.6%), while conventional optical systems have a high polarization sensitivity (>1%), resulting in radiation calibration errors.

[0007] The system is bulky: To achieve ultra-high spectral resolution (e.g., 0.05 nm), traditional solutions require complex optical path design. Even with the AHSI wide-band, wide-spectrum hyperspectral camera object-image dual-telecentric spectrometer technology, the size of the spectrometer is still difficult to meet the requirements of miniaturization of satellite-borne payloads.

[0008] To address the above problems, there is an urgent need to develop a satellite-borne detection system with ultra-high spectral resolution (<0.3nm), wide coverage (>150km), and low polarization sensitivity (<0.5%). Through coordinated hyperspectral and hyperspectral observations, accurate and synchronous inversion of chlorophyll fluorescence and vegetation physiological parameters can be achieved, providing a new generation of technical support for ecological remote sensing. Summary of the Invention

[0009] In order to solve the above technical problems, the present invention provides a space-borne sunlight-induced chlorophyll fluorescence spectrum detection and imaging system. By combining hyperspectral and hyperspectral observation methods, the system volume of the hyperspectral instrument is reduced to less than half of the traditional one while meeting the requirements of high spectral resolution, high spatial resolution, large field of view and low spectral distortion, thereby realizing the miniaturization, lightweight and integration of the space-borne sunlight-induced chlorophyll fluorescence spectrum detection and imaging system.

[0010] To achieve the above object, the present invention adopts the following technical solutions:

[0011] A spaceborne sunlight-induced chlorophyll fluorescence spectrum detection imaging system includes a telescope optical system, a field of view separator component, a hyperspectral spectrometer system and a high-spectral spectrometer system, wherein:

[0012] After the vegetation chlorophyll signal from the surface is focused by the telescope optical system, it is separated into a first field of view object signal and a second field of view object signal by a field of view separator component. The first field of view object signal is passed through a hyperspectral spectrometer system to obtain chlorophyll fluorescence information, and the second field of view object signal is passed through a hyperspectral spectrometer system to obtain vegetation photochemical index information;

[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 high-spectral spectrometer system, and the three systems cross the track and share a common field of view.

[0014] Furthermore, the telescope optical system is an image-space telecentric structure, with an operating band of 500-780nm, a field of view of 30°, a focal length of 189.5mm, an F number of 2.0-2.5, and a chief ray image-space telecentricity deviation of less than 2.5 degrees.

[0015] Furthermore, the field of view separator assembly is a roof reflector, and the two reflecting surfaces are respectively a hyperspectral field of view separator mirror and a hyperspectral field of view separator mirror. 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, the signal enters the hyperspectral instrument system through the second slit.

[0016] Furthermore, the first slit and the second slit are both field stops, and their lengths are 100 mm.

[0017] Furthermore, the hyperspectral spectrometer system includes a first slit protective plate, a plane turning mirror, a first meniscus correction lens, a third reflector, a grating and a hyperspectral detector; the first field of view object signal passes through the first slit protective plate, the plane turning mirror, the first meniscus correction lens, and the third reflector in sequence and is reflected to the grating, and after fine spectrometry by the grating, the light passes through the third reflector and the first meniscus correction lens again and is focused onto the hyperspectral detector; wherein, the first meniscus correction lens and the grating have a common optical axis; the first slit protective plate is tilted 1~2° to further reduce the polarization degree of the hyperspectral system.

[0018] Furthermore, the spectral range of the hyperspectral spectrometer system is 665-780nm, and the hyperspectral detector adopts 80μm×40μm pixel size. The spectral sampling interval is adjustable by controlling the sub-pixel splitting or merging output mode of the hyperspectral detector pixel, and the adjustment range is 0.06-0.24nm.

[0019] Furthermore, a narrow-bandpass linear gradient filter is integrated on the surface of the hyperspectral detector, and its single-channel spectral expansion width and starting and ending wavelengths correspond one-to-one to the expansion width and starting and ending wavelengths of each spectral channel after fine spectroscopy by the hyperspectrometer system.

[0020] Furthermore, the hyperspectral spectrometer system includes a second slit protective plate, a second meniscus correction lens, a first reflector, a convex grating, a second reflector, a spectrometer plane turning mirror and a hyperspectral detector. The second field of view object signal passes through the second slit protective plate, the second meniscus correction lens and the first reflector, is reflected and converged to the convex grating, and after fine spectrometry by the convex grating, reaches the second reflector and the second meniscus correction lens in turn to converge again, and is reflected to the hyperspectral detector through the spectrometer plane turning mirror; wherein, the second slit protective plate is tilted 1~2° to further reduce the polarization degree of the hyperspectral system.

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

[0022] Furthermore, each component of the telescope optical system, the field of view splitter assembly, the hyperspectral spectrometer system and the hyperspectral spectrometer system is coated with a depolarizing film.

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

[0024] The present invention adopts a hyperspectral spectrometer system and a high-spectral spectrometer system to simultaneously observe the spectral observation range of 500-650nm. Through accurate PRI and SIF information, it can accurately obtain vegetation reflectance, chlorophyll content, leaf area index, vegetation index, vegetation coverage and other information, and realize the synchronous observation of several important parameters in vegetation remote sensing, which helps to decouple the complex nonlinear relationship between fluorescence and photosynthesis, and can more effectively support the inversion application of total primary productivity, the monitoring application of chlorophyll fluorescence to environmental stress, and the monitoring application of surface biomass, water environment and soil organic matter.

[0025] The present invention achieves adjustable spectral sampling intervals by controlling the sub-pixel splitting or merging output mode of the detector pixels, solving the problem that the traditional single spectral resolution mode cannot meet the technical requirements of fluorescence detection. It is particularly necessary to achieve adjustable spectral sampling intervals and signal energy level matching functions through in-orbit programming. To meet the needs of fluorescence detection, the energy level matching design can improve the signal-to-noise ratio by more than 50% at the weak signals at the bottom of the two oxygen absorption bands O2-B (F687) and O2-A (F760).

[0026] The present invention adopts a narrow-bandpass linear gradient filter + a grating linear fine spectrometer system to achieve more precise filtering of the spectral channel, thereby more effective stray light suppression measures can increase the stray light suppression ratio by 300 times, and the stray light suppression ratio can reach the order of 10-9.

[0027] The present invention coats the optical mirror surface of each optical element with a depolarizing film, so that its linear polarization sensitivity is better than 0.5%. The depolarizing film can achieve highly efficient energy transfer, precise spectral realization, and additional polarization suppression of the system, so that S-polarized light and P-polarized light complement each other in intensity, and control the phase difference between S-polarized light and P-polarized light, so that the linear polarization sensitivity (LPS) of the entire optical system reaches a high control level.

[0028] Compared with traditional hyperspectral detection systems, the spectral resolution of this invention is improved by more than 10 times, while taking into account the requirements of large field of view, high spatial resolution, and low spectral distortion. Compared with traditional hyperspectral design schemes, the volume is reduced by nearly half, which greatly reduces the development and launch costs of satellite detection payloads, and realizes the miniaturization, lightweight and integration of satellite-borne sunlight-induced chlorophyll fluorescence spectrum detection imaging systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic diagram of a satellite-borne sunlight-induced chlorophyll fluorescence spectrum detection and imaging system of the present invention;

[0030] Figure 2 Schematic diagram of the optical system of the telescope of the present invention;

[0031] Figure 3a 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;

[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 Schematic diagram of the hyperspectral spectrometer system of the present invention;

[0034] Figure 4b This is a comparison diagram showing that the volume envelope of the hyperspectral spectrometer system of the present invention is significantly reduced 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 Schematic diagram of the diffuse speckle image quality designed for the hyperspectral spectrometer system of the present invention at a wavelength of 0.677 μm;

[0037] Figure 6b Schematic diagram of the design of diffuse speckle image quality at 0.7 μm wavelength for the hyperspectral spectrometer system of the present invention;

[0038] Figure 6c Schematic diagram of the diffuse speckle image quality designed for the hyperspectral spectrometer system of the present invention at a wavelength of 0.775 μm;

[0039] Figure 7a This is a schematic diagram of the diffuse speckle image quality designed for the hyperspectral spectrometer system of the present invention at a wavelength of 0.5 μm;

[0040] Figure 7b Schematic diagram of the design of diffuse speckle image quality at 0.59 μm wavelength for the hyperspectral spectrometer system of the present invention;

[0041] Figure 7c Schematic diagram of the design of diffuse speckle image quality at 0.68μm wavelength for the hyperspectral spectrometer system of the present invention;

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

[0043] Figure 9 Schematic diagram of stray light suppression according to the present invention;

[0044] Figure 10 Programming radiance comparison plot for spectral sampling interval;

[0045] Figure 11 Radiance comparison plot after programming the spectral sampling interval;

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

[0047] Reference numerals:

[0048] 1-1-telescope primary mirror, 1-2-telescope secondary mirror, 1-3-telescope tertiary mirror, 1-4-image plane;

[0049] 2-1-hyperspectral field of view separator mirror, 2-2-hyperspectral field of view separator mirror, 5-1-first slit, 5-2-second slit;

[0050] 3-1 - first slit protection plate, 3-2 - plane turning mirror, 3-3 - first meniscus correction lens, 3-4 - third reflecting mirror, 3-5 - grating, 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 turning mirror, 4-7-hyperspectral detector. DETAILED DESCRIPTION

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

[0053] like Figure 1 The satellite-borne sunlight-induced chlorophyll fluorescence spectrum detection imaging system of the present invention includes a telescope optical system, a field of view separator component, a hyperspectral spectrometer system and a high-spectral spectrometer system.

[0054] After the vegetation chlorophyll signal from the surface is focused by the telescope optical system, the vegetation chlorophyll signal is divided into a first field of view object signal and a second field of view object signal by a field of view separator component. The first field of view object signal obtains chlorophyll fluorescence information through the hyperspectral spectrometer system, and the second field of view object signal obtains the photochemical index information of the vegetation through the hyperspectral spectrometer system. The telescope optical system is 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, and maintains a cross-track common field of view to achieve imaging of the same area of the hyperspectral spectrometer system and the hyperspectral spectrometer system, so as to obtain completely matched chlorophyll fluorescence information and vegetation photochemical index information.

[0055] The optical system of the present invention adopts an off-axis three-mirror solution, which is unobstructed and has high optical efficiency, which is beneficial to improving the spectral channel detection sensitivity of the hyperspectral detection imager and is also conducive to subsequent optical-mechanical assembly and system engineering implementation. The parameters of the optical system of the present invention are shown in Table 1:

[0056] Table 1

[0057] As a preferred embodiment of the present invention, the numerical aperture of the optical system of the satellite-borne wide-band sunlight-induced chlorophyll fluorescence super-light detection spectrum imager is 0.1-0.3, the spectral resolution is less than 0.3nm, the pixel size is 80μm×40μm, and can be combined into a large pixel of 80μm×80μm.

[0058] like Figure 2 The telescope optical system of the present invention shown is a reflective optical system with an off-axis three-mirror structure, including a telescope primary mirror 1-1, a telescope secondary mirror 1-2 and a telescope tertiary mirror 1-3.

[0059] The telescope optical system of the present invention is different from ordinary imaging objective lenses. In addition to meeting some basic requirements of general imaging objective lenses, it usually has the following characteristics.

[0060] (1) Wide spectral coverage. Imaging spectrometers are characterized by a wide operating band, usually covering dozens or even hundreds of channels. This requires the telescope optical system to be able to meet the requirements of wide spectral range imaging. The wide imaging spectral range has little effect on reflecting telescopes, but for refracting or catadioptric telescopes, the large chromatic aberration caused by the wide band needs to be considered, which increases the difficulty of system aberration correction.

[0061] (2) Numerical aperture coupling. In order to ensure a high utilization rate of the spectroscopic instrument, the image-side numerical aperture of the telescope optical system 1 needs to be equal to the object-side numerical aperture of the two spectrometers in the optical system to achieve complete matching. If the numerical aperture of the telescope optical system is larger or smaller than the numerical aperture of any spectrometer, it will cause a waste of the imaging capability of the telescope optical system or spectrometer. Due to the limitation of the slit on the imaging field of view, the earth observation spectrometer usually requires a large relative aperture, that is, a small F number, in order to meet the instrument signal-to-noise ratio requirements. The F number in the visible light band is usually less than 3.5, and the infrared band system will require an even smaller F number, generally less than 2.5. This requires the telescope optical system to be designed as a system with a small F number to achieve complete matching with the spectrometer and increase the system's light collection capability.

[0062] (3) Image-space telecentric structure or approximately image-space telecentric structure. The imaging spectrometer consists of a telescope optical system and a spectrometer connected by a pupil. Since the spectrometer is usually an object-space telecentric structure, in order to match its pupil, the telescope optical system should be an image-space telecentric structure or an approximately image-space telecentric structure to achieve telecentricity matching. In the imaging spectrometer, the slit is the field stop. If the telescope optical system deviates from the image-space telecentric structure, the edge optics of the off-axis field of view will not be able to pass through the slit, resulting in vignetting, which in turn affects the signal-to-noise ratio of the instrument's field of view. In order not to affect the imaging performance of the instrument, the vignetting caused by deviation from the image-space telecentric structure must be controlled within 10% or the main ray deviation angle must be less than 2.5 degrees.

[0063] (4) The telescope optical system consists of a primary telescope mirror 1-1, a secondary telescope mirror 1-2, and a tertiary telescope mirror 1-3. The surface parameters of the primary telescope mirror 1-1 are: curvature radius R: -6000 mm, cone 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 mirror 1-2 are: curvature radius R: -404.98 mm, cone coefficient: 3.326, fourth-order aspheric coefficient: -1.48e-9, and sixth-order aspheric coefficient: -7 .476e-14; the surface parameters of the telescope's three mirrors 1-3 are curvature radius R: -423.07mm, cone coefficient is 0.157, fourth-order aspheric coefficient is -4.64e-11, and sixth-order aspheric coefficient is -9.97e-16; the axial distance between the telescope's primary mirror 1-1 and the telescope's secondary mirror 1-2 corresponding to the mother mirror is -411.15mm; the axial distance between the telescope's secondary mirror 1-2 and the telescope's three mirrors 1-3 corresponding to the mother mirror is 276.02mm, and the distance from the telescope's three mirrors 1-3 to the image plane 1-4 is -369.11mm.

[0064] Preferably, the telescope optical system of the present invention has an operating band of 500-780 nm, a field of view of 30°, a focal length of 189.5 mm, an F number of 2.0-2.5, and more preferably, an F number of 2.2.

[0065] The field of view separator assembly of the present invention is a roof reflector device, comprising a superspectral field of view separator mirror 2-1 and a hyperspectral field of view separator mirror 2-2.

[0066] The chlorophyll fluorescence signal collected by the telescope 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, the signal is separated into the second field of view object signal by the hyperspectral field separator mirror 2-2 and then enters the hyperspectral instrument system through the second slit 5-2. Figure 3b shown.

[0067] The first slit 5-1 and the second slit 5-2 are both field stops, which are located on both sides of the field separator and have a length of 100-110 mm. More preferably, the length of the first slit 5-1 and the second slit 5-2 are both 100 mm.

[0068] like Figure 4a The hyperspectral spectrometer system of the present invention shown includes a first slit protective plate 3-1, a plane turning mirror 3-2, a first meniscus correction lens 3-3, a third reflector 3-4, a grating 3-5 and a hyperspectral detector 3-6, wherein the first field of view object signal separated by the field of view separator mirror 2-1 passes through the first slit 5-1 and the first slit protective plate 3-1, and is deflected by the plane turning mirror 3-2, transmitted by the first meniscus correction lens 3-3, and converged to the grating 3-5 by the third reflector 3-4. After fine spectral separation by the grating, it is converged again by the third reflector 3-4 and passes through the meniscus correction lens 3-3 again to reach the hyperspectral detector 3-6; wherein the first meniscus correction lens 3-3 and the grating 3-5 share the same optical axis, the first meniscus correction lens 3-3 realizes common area multiplexing, and the third reflector 3-4 realizes common use, which reduces the volume of the hyperspectral spectrometer by more than 59%. Figure 4b As shown, in addition, the first meniscus correction lens 3-3 is designed as an equal-thickness lens, which reduces the difficulty of off-axis lens processing; the first slit protection sheet 3-1 is tilted 1~2° to further reduce the polarization degree of the hyperspectral system 3.

[0069] Due to the large asymmetry of conventional Offner spectrometers, it can be seen that in order to ensure that the dispersed light beam is not blocked by the grating, the off-axis amount of the slit is large, resulting in a large aperture of the correction lens, which is detrimental to the stability and engineering feasibility of the spectrometer and occupies a large amount of unnecessary weight and volume. Therefore, the present invention adjusts the structure of the conventional Offner spectrometer, so that the grating 3-5 and the first meniscus correction lens 3-3 share the same optical axis, allowing the light beam finely dispersed by the grating 3-5 to pass through the same area of the first meniscus correction lens 3-3 again, achieving the effect of reducing the volume and compact design. The present invention also converts the conventional hemispherical meniscus correction lens into a small meniscus prism and introduces a free-form surface into the third reflector 3-4, achieving a 300km field of view. The optical design spectral sampling interval is 0.1mm, and the spectral subdivision capability is doubled. The hyperspectral spectrometer system 3 of the present invention is a non-coaxial system (the third reflector 3-4 and the first meniscus correction lens 3-3 are not coaxial). This aims to improve the system's aberration-correcting degrees of freedom parameters. While ensuring a doubling of the field of view and enhanced spectral subdivision capability, spectral distortion is controlled within 0.3 pixels, spectral curvature is less than 0.3 pixels, and the RMS spectrometer image quality is less than 0.5 pixels. The third reflector 3-4 of the present invention is reused twice within the entire satellite-borne wide-band sunlight-induced chlorophyll fluorescence hyperspectral imaging system. This aims to simplify the spectrometer's structural complexity, reduce its size, and lower payload development and launch costs. Its corrective effect on spectral distortion (a type of aberration) is actually enhanced by using two reflectors; this is simply to simplify the optical system's complexity and reduce its size. To reduce the difficulty of developing the high-blaze-angle grating 3-5 and facilitate engineering development, the reflector 3-3 of the present invention can be a grating surface.

[0070] Preferably, the spectral range of the hyperspectral spectrometer system of the present invention is 665-780nm. In order to solve the problem that the traditional single spectral resolution mode cannot meet the needs of fluorescence detection, the spectrum sampling interval is adjustable and the signal energy level matching function is realized through on-track programming. The spectrum sampling interval adjustment range is 0.06-0.24nm. The spectrum sampling interval adjustment function is achieved by controlling the detector pixel sub-pixel splitting or merging output mode (such as 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 the pixel size d = 20 μm is used, the corresponding spectral sampling interval is 0.06 nm @ d = 20 μm. When the spectral dimensions are combined into one, the spectral sampling interval is 0.24 nm @ d = 80 μm. In response to the needs of fluorescence detection, the spectral sampling interval is adjustable to achieve matching of spectral sampling with the absorption peaks and valleys of the oxygen absorption band (e.g. Figure 10 and Figure 11Through energy level matching design, the signal-to-noise ratio can be improved by more than 50% at the weak signals at the bottom of the two oxygen absorption bands O2-B (F687) and O2-A (F760).

[0071] The structure of the spectrometer is relatively compact. As a preferred embodiment, the linear gradient filter is located on the hyperspectral detector 3-6 and is integrated with the detector. In order to better suppress stray light, the single-channel spectrum expansion width and the starting and ending wavelengths of the linear gradient filter of the present invention correspond to the expansion width and the starting and ending wavelengths of each spectral channel after fine spectral separation by the hyperspectral system, thereby improving the signal-to-noise ratio of the fine spectral channel. The diffuse spot size of the hyperspectral spectrometer system of the present invention is as follows: Figures 6a-6c shown.

[0072] The present invention adopts a linear gradient filter + linear beam splitter grating spectrometer system to achieve more accurate spectral channel filtering, such as Figure 8 As shown, due to the low light utilization rate of traditional stray light analysis methods, most light cannot reach the energy threshold after scattering within the optical machine and disappear. Only a small number of relatively obvious stray light paths can be discovered through simulation, and the remaining weak stray light paths are difficult to detect through simulation. However, based on the more precise and effective stray light suppression method of the present invention, light will be scattered in directions that are more conducive to entering the hyperspectral detectors 3-6, and even weaker stray light paths can be easily discovered through simulation. Secondly, the stray light paths discovered by the more precise and efficient stray light analysis method can also improve the stray light suppression ratio by 10 times by optimizing the internal structure of the telescope's sunshade, the secondary aperture of the optical machine structure, and the positions of the Rio aperture and field aperture.

[0073] Traditional stray light suppression measures can suppress most of the stray light energy, but there is no way to suppress the secondary and multi-level scattered energy in the detector front structure, such as Figure 9 As shown, the hyperspectral camera is different from other cameras. It uses the grating 3-5 to accurately split the light. The effective signal energy of each column is a narrow bandpass energy. Therefore, a linear gradient filter is designed in front of the hyperspectral detector 3-6 of the present invention. The filter area above the detector column pixel is a very narrow bandpass filter area. The wide-band stray light passes through the linear gradient filter, and only the light with a very narrow spectral bandwidth energy can pass through and be incident on the hyperspectral detector 3-6. By reasonably designing the bandwidth of the linear gradient filter, the stray light suppression ratio can be increased by 30 times. Through simulation analysis, the more effective stray light suppression measures designed by the present invention can increase the stray light suppression ratio by 300 times, and the stray light suppression ratio can reach 10 -9 Magnitude.

[0074] 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 reflector 4-3, a convex grating 4-4, a second reflector 4-5, a spectrometer plane deflection 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, and is transmitted through the second meniscus correction lens 4-2, converged by the first reflector 4-3 to the convex grating 4-4, and then finely split by the convex grating 4-4. It is then converged by the second reflector 4-5, passes through the second meniscus correction lens 4-2 again, and is deflected by the spectrometer deflection mirror 4-6 to reach the hyperspectral detector 4-7.

[0075] Preferably, the spectral range of the hyperspectral spectrometer system of the present invention is 500-680 nm, the spectral sampling interval is 2-4 nm, and more preferably, the spectral sampling interval is 3 nm.

[0076] As a preference, the diffuse spot size of the hyperspectral spectrometer system of the present invention is as follows: Figures 7a-7c shown.

[0077] In practical application, the chlorophyll fluorescence signal enters the telescope optical system, is sequentially focused by the telescope primary mirror 1-1, the telescope secondary mirror 1-2, and the telescope tertiary mirror 1-3, and then is separated into the first field of view object signal and the second field of view object signal by the field of view separator assembly;

[0078] The first field-of-view object signal is focused on the first slit 5-1 of the hyperspectral spectrometer system, then passes through the first slit protection plate 3-1, the plane deflection mirror 3-2, and the first meniscus correction lens 3-3 in sequence, is reflected by the reflector 3-4 and converges to the grating 3-5, and after fine separation by the grating 3-5, passes through the reflector 3-4 and the first meniscus correction lens 3-3 again and is focused on the hyperspectral detector 3-6;

[0079] The second field-of-view object signal is focused on the second slit 5-2 of the hyperspectral spectrometer system, then passes through the second slit protection plate 4-1 and the second meniscus correction lens 4-2, and is reflected by the first reflector 4-3 to the convex grating 4-4. After fine spectrometry by the grating, it is converged by the second reflector 4-5 and the second meniscus correction lens 4-2, and is turned to the hyperspectral detector 4-7 by the spectrometer turning mirror 4-6. The second slit protection plate 4-1 is tilted by 1~2° to further reduce the polarization degree of the hyperspectral system 4.

[0080] Furthermore, the present invention's satellite-borne wide-band sunlight-induced chlorophyll fluorescence hyperspectral detection and imaging system features a depolarizing film coated on all components, resulting in a linear polarization sensitivity better than 0.5%. The depolarizing film is required to perform functional functions on each optical surface: efficient energy transfer, precise spectral realization, and additional polarization suppression for the system.

[0081] In an optical system, any oblique incidence generates additional polarization, distorting the instrument's response to the received optical information. To control the instrument's additional polarization (quantified as linear polarization sensitivity (LPS)), systematic polarization control is achieved through the use of optical thin films applied to each optical surface. Based on a comprehensive design, the polarization spectra of individual components are measured and the design of thin film components with severe polarization separation is adjusted to achieve complementary intensities between S- and P-polarized light. This, combined with the phase difference between the two polarized light, allows for a high level of control over the LPS of the entire optical system.

[0082] In summary, the present invention can achieve very low system polarization sensitivity by controlling the following technical aspects:

[0083] (1) Control the linear polarization sensitivity of key components (such as meniscus lenses). Use high transmittance to control the clear separation of S-polarized light and P-polarized light without causing serious difficulties in system polarization control;

[0084] (2) Accurate measurement of linear polarization sensitivity of thin film components;

[0085] (3) Based on the polarization measurement results of a single element, the Jones matrix and the Mueller matrix are combined for calculation and analysis to obtain the polarization spectrum of the optical system and the values of LPS at different wavelengths and angles, providing support for system testing and correction.

[0086] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only 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 in the scope of protection of the present invention.

Claims

1. A spaceborne sunlight-induced chlorophyll fluorescence spectrum detection and imaging system, characterized in that: It includes a telescope optical system, a field of view splitter assembly, a hyperspectral spectrometer system and a high-spectral spectrometer system, wherein: After the vegetation chlorophyll signal from the surface is focused by the telescope optical system, it is separated into a first field of view object signal and a second field of view object signal by a field of view separator component. The first field of view object signal is passed through a hyperspectral spectrometer system to obtain chlorophyll fluorescence information, and the second field of view object signal is passed through a hyperspectral spectrometer system to obtain vegetation photochemical index information; 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 high-spectral spectrometer system, and the three systems cross the track and share a common field of view.

2. The spaceborne sunlight-induced chlorophyll fluorescence spectrum detection and imaging system according to claim 1, characterized in that: The telescope optical system is an image-space telecentric structure, with an operating band of 500-780nm, a field of view of 30°, a focal length of 189.5mm, an F number of 2.0-2.5, and a chief ray image-space telecentricity deviation of less than 2.5 degrees.

3. The spaceborne sunlight-induced chlorophyll fluorescence spectrum detection and imaging system according to claim 1, characterized in that: The field of view separator component is a roof reflector, and the two reflecting surfaces are respectively a hyperspectral field of view separator mirror (2-1) and a high-spectral 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 a first slit (5-1). After being separated into a second field of view object signal by the high-spectral field of view separator mirror (2-2), the signal enters the high-spectral instrument system through a second slit (5-2).

4. The spaceborne sunlight-induced chlorophyll fluorescence spectrum 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, and their lengths are 100 mm.

5. The spaceborne sunlight-induced chlorophyll fluorescence spectrum detection and imaging system according to claim 1, characterized in that: The hyperspectral spectrometer system comprises a first slit protective plate (3-1), a plane deflection mirror (3-2), a first meniscus correction lens (3-3), a third reflector (3-4), a grating (3-5) and a hyperspectral detector (3-6); a first field-of-view object signal passes through the first slit protective plate (3-1), the plane deflection mirror (3-2), the first meniscus correction lens (3-3) and the third reflector (3-4) in sequence, and is then reflected to the grating (3-5); after finely splitting by the grating (3-5), the light again passes through the third reflector (3-4) and the first meniscus correction lens (3-3) and is focused onto the hyperspectral detector (3-6); wherein the first meniscus correction lens (3-3) and the grating (3-5) share a common optical axis.

6. The spaceborne sunlight-induced chlorophyll fluorescence spectrum detection and imaging system according to claim 5, characterized in that: The spectral range of the hyperspectral spectrometer system is 665-780nm, and 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), and the adjustment range is 0.06-0.24nm.

7. The spaceborne sunlight-induced chlorophyll fluorescence spectrum detection and imaging system according to claim 5, characterized in that: The surface of the hyperspectral detector (3-6) is integrated with a narrow-bandpass linear gradient filter, and the single-channel spectral expansion width and starting and ending wavelengths thereof correspond one-to-one to the expansion width and starting and ending wavelengths of each spectral channel after fine spectral separation by the hyperspectrometer system.

8. The spaceborne sunlight-induced chlorophyll fluorescence spectrum detection and imaging system according to claim 1, characterized in that: The hyperspectral spectrometer system comprises a second slit protective 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 turning mirror (4-6) and a hyperspectral detector (4-7). The second field-of-view object signal passes through the second slit protective plate (4-1), the second meniscus correction lens (4-2) and the first reflecting mirror (4-3), is reflected and converged to the convex grating (4-4), is finely split by the convex grating (4-4), sequentially reaches the second reflecting mirror (4-5) and the second meniscus correction lens (4-2), is converged again, and is reflected to the hyperspectral detector (4-7) by the spectrometer plane turning mirror (4-6).

9. The spaceborne sunlight-induced chlorophyll fluorescence spectrum detection and imaging system according to claim 8, characterized in that: The spectral range of the hyperspectral spectrometer system is 500-680nm, and the spectral sampling interval is 2-4nm.

10. The spaceborne sunlight-induced chlorophyll fluorescence spectrum detection and imaging system according to claim 1, characterized in that: Each component of the telescope optical system, the field of view splitter assembly, the hyperspectral spectrometer system and the hyperspectral spectrometer system is plated with a depolarizing film.

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