A chlorophyll fluorescence imaging system, imaging method and application

Abstract

This invention relates to the field of remote sensing imaging systems, and more particularly to a chlorophyll fluorescence imaging system, imaging method, and application. The imaging system includes a housing, an imaging lens, a moving assembly, and a processor. The imaging lens is mounted on the moving assembly and extends outside the housing. The moving assembly is used to move the imaging lens. Inside the housing, from the imaging lens backwards, are arranged a slit, a first lens group, a grating, a second lens group, and an area array detector. A light intensity acquisition module is located on one side of the slit. The slit and the first lens group are both parallel to the imaging lens. The first and second lens groups are not parallel to the grating, and are not parallel to each other. The processor is located inside the housing and is electrically connected to the moving assembly and the area array detector. An electronic interface for outputting data is installed on the outer wall of the housing and is electrically connected to the processor. This invention can achieve fluorescence imaging with high spectral resolution, high spatial resolution, and a high signal-to-noise ratio.

Description

Technical Field

[0001] This invention relates to the field of remote sensing detection imaging systems, and more particularly to a chlorophyll fluorescence imaging system, imaging method, and application. Background Technology

[0002] Hyperspectral imaging technology is based on a wide range of narrow-band image data. It combines imaging and spectral techniques to detect the two-dimensional geometric space and one-dimensional spectral information of a target, acquiring continuous, narrow-band image data with high spectral resolution. By acquiring the spectral information of an object in different bands, it enables rapid identification and quantitative analysis of the object. Hyperspectral imaging technology features a vast number of bands (hundreds of bands), high spectral resolution (several nm), and narrow bands (≤10). -2 Hyperspectral imaging is characterized by its wide spectral range (200-2500 nm) and the integration of image and spectrum. Its advantages lie in the rich information captured in the images, high recognition accuracy, and the availability of multiple data description models. Because the reflectance spectrum of an object exhibits a "fingerprint" effect, different substances can be distinguished based on the principle that different substances have different spectra, and the same substance will have the same spectrum, combined with hyperspectral imaging technology. Currently, hyperspectral imaging technology is widely used in agriculture, environmental monitoring, geological exploration, remote sensing, and medicine.

[0003] Sun-induced chlorophyll fluorescence (SIF) is the spectral signal (650-800 nm) emitted by the photosynthetic centers of plants under sunlight. It has two peaks: red (around 690 nm) and near-infrared (around 740 nm), directly reflecting the dynamic changes in actual photosynthesis. SIF remote sensing is a rapidly developing vegetation remote sensing technology that can compensate for the shortcomings of current vegetation remote sensing observations, providing new ideas and technologies for terrestrial ecosystem carbon cycling and vegetation monitoring. Vegetation remote sensing technologies, represented by vegetation indices based on "greenness" observations (such as the Normalized Difference Vegetation Index NDVI), have greatly promoted the understanding and knowledge of the Earth's biosphere on a macroscopic scale over the past 30 years. However, they can only detect the "potential photosynthesis" of plants through "greenness." Chlorophyll fluorescence imaging technology has unique technical advantages in detecting vegetation photosynthetic physiology and is a direct method for detecting "actual photosynthesis." At the same time, it is also a major breakthrough based on the current non-imaging SIF system. From traditional spectral research to the current research and application mode based on the integration of "image and spectrum", it can be said that vegetation chlorophyll fluorescence imaging is the most groundbreaking research frontier in the field of vegetation remote sensing in the past 10 years.

[0004] A hyperspectral imager (also known as a spectrophotometer or hyperspectral camera) is a non-destructive testing and analysis instrument that perfectly combines an imaging spectrometer and an area array detector, enabling simultaneous and rapid acquisition of spectral and image information. The imaging spectrometer images a line on the target at a time and disperses the light so that each spectral component corresponds to a pixel on the linear array. Therefore, each image from an imaging spectrometer consists of linear array pixels in one dimension (spatial axis) and spectral distribution (intensity of light in spectral elements) in another dimension (spectral axis). Typically, the main components of an imaging spectrometer are: a collimating lens, a spectrometer, and a focusing lens.

[0005] like Figure 1 The diagram shows a typical system structure of an imaging spectrometer based on the Offner structure. Its beam-splitting structure generally adopts an off-axis three-reflection structure based on a Rowland circle, consisting of a first concave mirror, an ellipsoidal convex grating, and a second concave mirror. The first, second, and ellipsoidal concave mirrors are confocal, sharing the same focal point and optical axis. The first and second ellipsoidal concave mirrors are located on opposite sides of the principal plane perpendicular to the major axis. The ellipsoidal convex grating is distributed on both sides of the principal plane perpendicular to the major axis. The minor semi-axis of the second ellipsoid is half the projection distance from the entrance slit to the first ellipsoidal concave mirror along the optical axis. The entrance slit and the detection unit are placed near the two focal points. While this optical system boasts advantages such as compact structure, low inherent aberrations, high light energy utilization, and high resolution, its imaging principle is as follows: light emitted from the object surface is reflected by the first concave spherical mirror, then split by a convex spherical grating to obtain monochromatic diffracted light. This monochromatic diffracted light is then reflected and focused onto the image plane by a second concave spherical mirror. Therefore, except for rays incident at different angles on the meridional plane that have the same optical path difference with the principal ray passing through the principal axis, rays incident at different angles on other planes have different optical path differences with the principal ray. Consequently, the off-axis three-reflection beam-splitting structure of the Rowland circle can only ensure that rays incident on the meridional plane have the same optical path difference with the principal ray passing through the principal axis, and can only eliminate meridional aberration, but cannot simultaneously address the effects of other aberrations, resulting in relatively poor image quality.

[0006] like Figure 2 The diagram shows a schematic of another common imaging spectrometer system based on a prism-grating-prism (PGP) combination element, where the prism-grating-prism serves as the beam-splitting structure. In this system, a volume holographic phase grating can be used, achieving high diffraction efficiency. The collimating and imaging mirrors employ a symmetrical structure, effectively eliminating lateral aberrations. However, ghosting remains a problem even with the grating-prism combination. The specific reasons are as follows:

[0007] like Figure 3 and Figure 4As shown, taking a system containing a prism as an example for analysis, the system's beam-splitting structure includes a first imaging lens group B, a grating C, a wedge prism D, and a second imaging lens group E. First, the first imaging lens group B collimates the image from the entrance slit A (entrance slit dimensions: length 16mm, width 30μm) to make it collimated parallel light. Then, after dispersion by the grating C, it forms monochromatic light of different wavelengths. The monochromatic light continues to enter the wedge prism D, which can deflect the beam incident directly on the vertical surface of the prism by 2° to 10°. The wedge prism D can be used for beam steering applications. The grating dispersion width is closely related to the deflection angle of the wedge prism. Then, the monochromatic light output from the wedge prism is collimated by the second imaging lens group E to form parallel light. This parallel light is mapped onto the target surface of the array detector, where the dimensions of the array detector target surface are: X-axis: 13.3mm (6.5μm*2048), Y-axis: 13.3mm (6.5μm*2048). That is, the width of the monochromatic light output after passing through the grating and prism is within 13.3mm, and in reality it is around 10mm. The number of grating lines and the beam deflection angle have an impact on this dispersion width.

[0008] A grating, whether a transmission diffraction grating or a reflection diffraction grating, can separate light of different wavelengths through a repeating structure within the grating. This structure affects the amplitude and / or phase of the incident light, causing interference in the outgoing light. Taking a common transmission grating as an example... Figure 5 As shown, it features a series of repeating narrow grooves spaced α apart etched on a transparent substrate. This repeating structure can be viewed as a series of closely spaced slits, creating an area where light can be scattered. Light travels at an angle θ. i Incident on the grating, by solving for illuminance as a function of wavelength and slit position, we obtain a general expression applicable to θ. i All diffraction gratings at 0°:

[0009] αsin(θ m )=mλ (1)

[0010] This equation is called the grating equation. This equation shows that, depending on the value of mλ, a grating with a spacing of α will diffuse light at discrete angles (θ). m Deflection, where m is the principal maximum order and θ is the diffraction angle. m It is the exit angle measured orthogonally to the surface of the diffraction grating. It is easy to see from equation (1) that for a given order m, light of different wavelengths will exit the grating at different angles. For a white light source, this corresponds to a continuous spectrum dependent on the angle. Using geometric transformations and equation (1), the expression for the transmission grating can be obtained:

[0011] α[sin(θ m )-sin(θ i)]=mλ (2)

[0012] However, when the beam-splitting structure is designed with a wedge prism, ghost images can occur in specific regions due to the scattering effect between diffraction orders. This is because although the grating has high diffraction efficiency in the first order over a wide bandwidth and the scattering between different diffraction peaks is extremely low with almost no ghosting, some stray light effects can still occur, such as... Figure 6 In the obtained image shown, the horizontal bright band appears as an unusually prominent peak in the spectrum (e.g., Figure 7 (As shown), this seriously affects imaging quality and spectral accuracy.

[0013] Therefore, when the aforementioned common hyperspectral imaging systems are applied to the field of SIF remote sensing detection, they still cannot fully meet the usage requirements. Thus, there is an urgent need to develop a hyperspectral imaging system suitable for SIF remote sensing detection. Summary of the Invention

[0014] To address the above problems, this invention provides a chlorophyll fluorescence imaging system, imaging method, and application scheme combined with a drone.

[0015] To achieve the above objectives, the present invention provides a chlorophyll fluorescence imaging system, specifically:

[0016] A chlorophyll fluorescence imaging system includes a housing, an imaging lens, a moving assembly, and a processor. A mounting hole is provided on one side wall of the housing. The imaging lens is mounted on the moving assembly and extends through the mounting hole beyond the housing; the width of the mounting hole is greater than the width of the imaging lens. The moving assembly is located inside the housing and is used to move the imaging lens laterally along the mounting hole. Inside the housing, from the imaging lens backwards, are arranged a slit, a first lens group, a grating, a second lens group, and an area array detector. One side of the slit of the slit is equipped with a light intensity sensor for collecting the intensity of the light source. The system comprises a module; the slit and the first lens group are both arranged parallel to the imaging lens; the grating is not parallel to the first lens group; the second lens group is not parallel to the grating, and the second lens group is not parallel to the first lens group; the optical path formed by the imaging lens, the slit, the light intensity acquisition module, the first lens group, the grating, the second lens group, and the area array detector is enclosed within a housing; the processor is located within the housing and is electrically connected to the moving components and the area array detector; an electronic interface for outputting data is installed on the outer wall of the housing, and the electronic interface is electrically connected to the processor.

[0017] The light intensity acquisition module is made of optical fiber.

[0018] Preferably, the moving component includes a motor, a lead screw, and a connecting block. The motor is installed inside the housing and its output shaft is fixedly connected to one end of the lead screw. The mounting part of the imaging lens is fixedly connected to the lead screw nut on the lead screw via the connecting block. The motor is controlled by a processor.

[0019] As an improvement, a telescopic dustproof baffle is provided on the side wall of the mounting hole.

[0020] As an improvement, an auxiliary camera is also included, which is mounted on one side of the imaging lens and is used to monitor the field of view of the imaging lens. The auxiliary camera is electrically connected to the processor.

[0021] As an improvement, a heat dissipation structure is provided on the casing.

[0022] As an improvement, a fan located inside the casing is also included.

[0023] To achieve the above objectives, the present invention also provides an imaging method for a chlorophyll fluorescence imaging system, specifically comprising:

[0024] The imaging methods of the chlorophyll fluorescence imaging system specifically include:

[0025] The processor controls the movement of the moving components;

[0026] The imaging lens moves according to a predetermined stroke under the drive of the moving component to perform push-broom acquisition of the target under test;

[0027] The target under test is focused by the imaging lens and imaged on the slit. Then, after collimation by the first lens group, grating dispersion, and second lens group, the image of the target under test is output to the area array detector. The illumination intensity acquisition module simultaneously acquires the illumination intensity of the light source and outputs the illumination intensity image to the area array detector after slit imaging, collimation by the first lens group, grating dispersion, and second lens group.

[0028] The processor receives and stores the output information of the array detector, and outputs the output information to the outside of the imaging system through an electronic interface.

[0029] As an improvement, when the imaging system also includes an auxiliary camera, the imaging method is as follows:

[0030] The auxiliary camera monitors the field of view of the imaging lens and feeds the field of view information back to the processor;

[0031] The processor controls the movement of the moving components;

[0032] The imaging lens moves according to a predetermined stroke, driven by the moving components, to perform push-broom data acquisition on the target under test;

[0033] The target under test is focused by the imaging lens and imaged on the slit. Then, after collimation by the first lens group, grating dispersion, and second lens group, the image of the target under test is output to the area array detector. The illumination intensity acquisition module simultaneously acquires the illumination intensity of the light source and outputs the illumination intensity image to the area array detector after slit imaging, collimation by the first lens group, grating dispersion, and second lens group.

[0034] The processor receives and stores the output information of the array detector and the auxiliary camera, and outputs this output information to the outside of the imaging system through an electronic interface.

[0035] To achieve the above objectives, the present invention also provides an unmanned aerial vehicle (UAV) chlorophyll fluorescence imaging system, comprising the aforementioned chlorophyll fluorescence imaging system, wherein the chlorophyll fluorescence imaging system is fixed on the UAV.

[0036] The present invention has the following beneficial effects:

[0037] 1. The chlorophyll fluorescence imaging system based on the transmission imaging principle described in this invention adopts a prism-free imaging method. In this mode, the dispersion angle of the monochromatic light output by the grating will be large, forming structural irregularities and eliminating the existence of ghost images.

[0038] 2. The chlorophyll fluorescence imaging system based on the transmission imaging principle described in this invention can achieve signal detection in the 650nm-800nm ​​spectral range, and at the same time, it can obtain images with high spectral resolution, high spatial resolution, and high signal-to-noise ratio.

[0039] 2. The chlorophyll fluorescence imaging system based on the transmission imaging principle described in this invention adopts a lens scanning imaging method and is a fluorescence hyperspectral imaging system that integrates acquisition, control, real-time data calibration and processing.

[0040] 3. The chlorophyll fluorescence imaging system based on the transmission imaging principle described in this invention can achieve synchronization of uplink and downlink information through a unique light intensity collection and acquisition method, which not only ensures the independence of the beam splitting path, but also achieves a high degree of system consistency.

[0041] 4. When the chlorophyll fluorescence imaging system based on the transmission imaging principle described in this invention is combined with UAV-borne technology, the application scheme of combined data calibration, stitching and real-time correction provides better efficiency for fluorescence imaging based on higher resolution. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the system structure of an imaging spectrometer based on the Offner structure;

[0043] Figure 2This is a schematic diagram of the system structure of an imaging spectrometer based on a prism-grating-prism (PGP) combined element;

[0044] Figure 3 This is a schematic diagram of an imaging spectrometer system containing prisms;

[0045] Figure 4 This is a schematic diagram of an imaging spectrometer system containing prisms;

[0046] Figure 5 This is a diagram illustrating the working principle of a grating.

[0047] Figure 6 This is an image of the existing imaging spectrometer system containing a prism;

[0048] Figure 7 This is a spectral data graph of an existing imaging spectrometer system containing a prism;

[0049] Figure 8 This is a schematic diagram of the structure of the present invention;

[0050] Figure 9 This is a schematic diagram of the internal structure of the present invention;

[0051] Figure 10 This is a bottom view of the present invention;

[0052] Figure 11 This is a partial structural cross-sectional view of the present invention;

[0053] Figure 12 This is a partial structural schematic diagram of the present invention;

[0054] Figure 13 This is a partial structural schematic diagram of the present invention;

[0055] Figure label:

[0056] 1. Housing; 101. Upper outer shell; 102. Side panel; 103. Bottom panel; 104. Telescopic dustproof baffle; 105. Heat dissipation structure;

[0057] 2. Imaging lens;

[0058] 3. Slit plate, 301. Slit;

[0059] 4. Light intensity acquisition module;

[0060] 5. Moving component; 501. Motor; 502. Lead screw; 503. Lead screw nut; 504. Connecting block;

[0061] 6. First lens group; 601. First convex lens; 602. Second convex lens; 603. First plano-convex lens; 604. Second plano-convex lens;

[0062] 7. Grating; 701. Grating fixing component;

[0063] 8. Second lens group; 801. Third plano-convex lens; 802. Fourth plano-convex lens; 803. Third convex lens; 804. Fourth convex lens;

[0064] 9. Area array detector;

[0065] 10. Processor;

[0066] 11. Fan;

[0067] 12. Auxiliary camera;

[0068] 13. Electronic interface;

[0069] 14. Shell. Detailed Implementation

[0070] Combination Figures 8 to 13 (in Figures 11-13 The following is a partial structural diagram (containing only an imaging lens, a slit, a light intensity acquisition module, a first lens group, a grating, a second lens group, an area array detector, and a housing for sealing the optical path) to describe the embodiments of the present invention in detail, but does not limit the claims of the present invention in any way.

[0071] Example 1

[0072] like Figure 8-13 As shown, the chlorophyll fluorescence imaging system includes a housing, an imaging lens, a slit, a light intensity acquisition module, a moving component, a first lens group, a grating, a second lens group, an area array detector, and a processor.

[0073] in:

[0074] A mounting hole is provided on one side wall of the housing. The imaging lens is mounted on the moving component and extends out of the housing through the mounting hole. The width of the mounting hole is greater than the width of the imaging lens.

[0075] The moving component is located inside the housing and is used to drive the imaging lens to move laterally along the mounting hole. The moving component includes a motor, a lead screw, and a connecting block. The motor is installed inside the housing and its output shaft is fixedly connected to one end of the lead screw. The mounting part of the imaging lens is fixedly connected to the lead screw nut on the lead screw through the connecting block. The motor is controlled by the processor.

[0076] Inside the housing, from the self-imaging lens backwards, a slit, a first lens group, a grating, a second lens group, and an area array detector are arranged in sequence.

[0077] A light intensity acquisition module for collecting light intensity from a light source is provided on one side of the slit.

[0078] The slit and the first lens group are both set parallel to the imaging lens;

[0079] The grating is not parallel to the first lens group;

[0080] The second lens group is not parallel to the grating, and the second lens group is not parallel to the first lens group;

[0081] The optical path formed by the imaging lens, slit, light intensity acquisition module, first lens group, grating, second lens group and area array detector is enclosed in a housing;

[0082] The processor is located inside the casing and is electrically connected to the moving components and the area array detector;

[0083] An electronic interface for outputting data is installed on the outer wall of the casing, and the electronic interface is electrically connected to the processor.

[0084] Example 2

[0085] like Figure 8-13 As shown, considering that the hyperspectral spatial scanning imaging process of the imaging lens is push-broom imaging, it is difficult to accurately judge the target under test in the slit, and thus it is impossible to accurately control the imaging lens to acquire images of the target under test. Based on embodiment 1, an improvement is made by installing an auxiliary camera on one side of the imaging lens to monitor the field of view of the imaging lens in real time. The auxiliary camera is electrically connected to the processor.

[0086] Example 3

[0087] like Figure 8-13 As shown, considering that the imaging systems of Embodiment 1 and Embodiment 2 have high requirements for ambient temperature, the heat dissipation performance of the system is improved by the following means based on Embodiment 1 or Embodiment 2:

[0088] 1. A heat dissipation structure is provided on the casing. The heat dissipation structure can take the form of heat dissipation holes, heat dissipation windows, etc. The shape of the heat dissipation holes can be circular, strip-shaped, or irregular, etc. These shapes can be used individually or in combination, as long as the required heat dissipation effect can be guaranteed.

[0089] 2. Based on the heat dissipation structure, a cooling fan can be further installed inside the casing to dissipate heat from the imaging system. The fan allows the heat generated by the imaging structure of the casing to be quickly expelled outside the casing through the heat dissipation structure.

[0090] In summary, the design of the heat dissipation structure and fan ensures that the electronic components and optical structures inside the casing are protected from high temperatures during operation or when affected by external ambient temperatures, keeping each unit within the specified operating temperature range.

[0091] For the above three embodiments, the following preferred designs or improvements can be made:

[0092] 1. The housing can be constructed using an upper outer shell, a bottom panel, and at least two side panels. The bottom and side panels can be integrally molded. The shape of the upper outer shell and the shape and number of the side panels are determined by the overall shape formed after assembly of the "imaging lens, slit plate, light intensity acquisition module, moving component, first lens group, grating, second lens group, area array detector, and processor," with the primary considerations being maximizing internal installation space savings, reducing overall housing volume, and ensuring imaging system performance. Aluminum alloy is preferred for the housing, as it not only reduces the overall system weight, facilitating in-depth application development on small airborne platforms, but also lowers costs while providing sufficient strength to ensure system stability and safety. Retractable dustproof baffles can be installed on the side walls of the housing mounting holes to provide varying degrees of shielding based on the movement of the imaging lens, preventing external dust and other contaminants from entering the housing.

[0093] 2. The preferred imaging lens is a standard C-mount lens with a back focal length of 17.52mm. As a standard component of the system, a standard C-mount lens can be selected to meet different shooting requirements with varying fields of view and focal lengths. The system's entrance slit is linear with a length of 16mm. Choosing a standard C-mount lens results in a target surface size between 18-20mm. If an F-mount-like structure were chosen, the imaging effect would be difficult to control, and the weight would be greater than that of a standard C-mount lens. Furthermore, choosing a standard C-mount lens ensures achromatic performance within its application wavelength range, while other F-mount-like lenses only meet visible wavelength requirements and lack achromatic capability in the near-infrared region. Considering that lens distortion is also a significant factor affecting imaging performance, and because the system uses lens scanning, the relative dimensions of the slit length and the lens target surface must be matched.

[0094] 3. The total effective stroke length of the moving component driving the imaging lens can be selected as 1.2cm. At this size, the moving component will not significantly increase the volume of the imaging system or the opening size of the imaging lens mounting hole on the housing, and can ensure that the imaging lens push-scan range is greater than 1cm. Considering that the system may be equipped with a drone for hovering push-scanning, in addition to the line field of view width (determined by the slit length), there is another dimension, which is the field of view width of the scanning dimension. When the drive motor moves the lens, the greater the stroke, the larger the image area formed, which will also improve the overall acquisition efficiency of the system.

[0095] 4. After the image of the target to be tested is focused by the imaging lens, it is imaged on the slit. The preferred size of the slit is: length 16mm and width 30μm.

[0096] 5. The light intensity acquisition module uses optical fiber. Approximately 4-5mm of space in the slit is reserved for the installation and fixation of the optical fiber. The fiber core diameter is fixed to align with the slit. The optical fiber can be 1.5m in length and 100μm or 200μm in core diameter. A larger core diameter (100μm or 200μm) results in better light throughput. Because the system design directly images the information acquired by the optical fiber onto the entrance slit, and the slit is used simultaneously throughout the system to acquire both the image of the target and the light intensity, even though the source of the target image may differ, the images converge after entering the lens, grating, and area array detector through the slit and are recorded synchronously. This ensures both the image of the target and the illumination required for correction, achieving the capability of simultaneous frame acquisition and recording.

[0097] 6. The grating can be a transmissive blazed grating, which can be installed inside the housing through the grating fixing parts.

[0098] 7. The first lens group collimates the composite light information after passing through the slit to form parallel light; this parallel light enters the grating, and the grating disperses the light entering it to form monochromatic light at different angles.

[0099] 8. The second lens group collimates and focuses different monochromatic lights, and finally maps the spatial dimension (slit correspondence) and spectral dimension (grating dispersion) onto the target surface of the array detector. On the target surface of the detector, although it is intuitive to only record the information of the target's spatial dimension, in fact, the corresponding spectral information after grating dispersion is hidden at different pixels in this spatial dimension.

[0100] 9. Area array detectors can be SCMOS detectors, CCD cameras, etc. Photoelectric conversion is achieved through SCMOS detectors or CCD cameras, and visualization and digital output are realized through these photosensitive components. Relatively speaking, SCMOS detectors can achieve a better signal-to-noise ratio.

[0101] 10. When applying this invention, the angle between the grating and the first lens group, the angle between the grating and the second lens group, and parameters such as the focal length of the first lens group, the number of grating lines, the focal length of the second lens group, the required spectral response range for the application, and the size and corresponding center position of the array detector target surface are closely related. Selection must be made based on the specific application. For example, a specific application of this application is described below:

[0102] The required spectral response range is 650-800nm; the detector target area is 13.3mm*13.3mm (2048*6.5um); the spectral resolution is 0.3nm; the optical numerical aperture is F2.0; and the grating dispersion area is a maximum of 13.3mm.

[0103] Both the first and second lens groups have a focal length of 50mm. The first lens group consists of four lens elements, whose properties and spatial positions are designed to meet the 50mm fixed focal length imaging requirements. The second lens group has the same lens composition as the first lens group, except that it is arranged in a mirror-symmetrical manner with the grating as the center. Figure 11 As shown, from the imaging lens toward the grating, the first lens group sequentially includes a first convex lens, a second convex lens, a first plano-convex lens, and a second plano-convex lens, and the second lens group sequentially includes a third plano-convex lens, a fourth plano-convex lens, a third convex lens, and a fourth convex lens.

[0104] The grating employs a high-density etched (1200 l / mm) transmission diffraction blazed grating with a blaze wavelength of 840nm to achieve spectral dispersion and generate monochromatic light output. Because it needs to decompose the parallel light output from the first lens group, the monochromatic light separated by the grating needs to be collimated by the second lens group, ensuring that the collimated light is mapped onto different pixels of the detector. Simultaneously, it must guarantee the characteristic spectral response range (650nm-800nm ​​region), extremely high spectral resolution (0.3nm), and meet the requirement that the maximum dispersion region area is 2048 * 6.5um = 13.3mm. Therefore, it needs to have a certain optical angular relationship with the first lens group. Figure 4 Based on the expression for the transmission grating mentioned in the background art, it can be concluded that the angle between the grating and the first lens group is preferably 34.5 degrees, and the angle between the grating and the second lens group is preferably 34.5 degrees.

[0105] In practical applications of the system described in this invention, the selection and parameters of the grating, the composition and parameters of the first lens group, the composition and parameters of the second lens group, and the selection and parameters of the area array detector are not limited to the above-mentioned examples. Instead, specific selections and configurations are made according to the needs of the application to meet the spectral performance output requirements of the application.

[0106] 11. The electronic interface shall include at least a USB 3.0 interface and an HDMI interface. These two interfaces are currently the most widely used interfaces, which can efficiently and comprehensively transmit the output information of the array detector to external devices (such as computers) and ensure the reliability of the imaging system's data output performance.

[0107] 2. The auxiliary camera is preferably a 500W pixel RGB camera with an 80° field of view, and the communication method is USB3.0.

[0108] 13. The fan is preferably designed to operate at DC 5V and blow air inwards.

[0109] 14. The heat dissipation structure can be made of aluminum-magnesium alloy, which is lighter in weight than traditional aluminum material, while still ensuring good strength.

[0110] 15. The entire chlorophyll fluorescence imaging system can be mounted on a drone for use. The system can be powered by the drone or by other power supply methods.

[0111] The overall working principle of the present invention will be explained below using Example 2 as an example:

[0112] The auxiliary camera monitors the field of view of the imaging lens and feeds the field of view information back to the processor;

[0113] The processor combines field-of-view information to control the movement of mobile components;

[0114] The imaging lens moves according to a predetermined stroke under the drive of the moving component, and performs push-broom imaging of the target under test;

[0115] The target under test is focused by the imaging lens and imaged on the slit. Then, after collimation by the first lens group, grating dispersion, and second lens group, the image of the target under test is output to the area array detector. The light intensity acquisition module simultaneously acquires the light intensity of the light source (the light source can be sunlight or its special auxiliary light source, depending on the application scenario), and after slit imaging, collimation by the first lens group, grating dispersion, and second lens group, the light intensity image is output to the area array detector.

[0116] The processor receives and stores the output information of the array detector and the auxiliary camera, and outputs this output information to the outside of the imaging system through an electronic interface.

[0117] Based on the above working principle, it can be concluded that:

[0118] 1. When the target under test is static, the imaging spectrometer (i.e., the imaging optical structure consisting of a slit, a first lens group, a grating, and a second lens group) and the area array detector integrated inside the housing are a single structure and will not move in space. When the system is imaging, it relies on the moving component to drive the imaging lens to move in space, thereby realizing hyperspectral spatial scanning imaging.

[0119] 2. Sunlight intensity information or other light source intensity information is collected by the light intensity acquisition module and enters the imaging spectrum module (i.e., the imaging optical structure composed of a slit, a first lens group, a grating, and a second lens group) and the area array detector as the light detection unit. This allows the area array detector to record the light intensity information of the corresponding light source while acquiring each frame of target data, thus achieving simultaneous acquisition of the target image and the illumination information. In other words, the detector can synchronously record the image information of the target and the illumination information.

[0120] 3. The auxiliary camera, serving as a monitoring unit, aims to locate the area captured by the imaging system for easier observation and adjustment. It also provides a set of synchronized RGB images of the area for subsequent data and image processing. The auxiliary camera's field of view is designed to be significantly larger than that of the imaging lens in the imaging system. Software modifications to corresponding parameters ensure consistency between the captured and monitored areas. Furthermore, it provides image references for subsequent data image stitching, calibration, and correction, and can also serve as an auxiliary tool or diagram to provide a basis for assessing data acquisition quality.

[0121] 4. The electronic interface serves as the external output interface of the imaging system, aiming to connect internal units (auxiliary cameras, area array detectors, drive motors, etc.) with external terminals. The system does not transmit acquired data to the ground terminal in real time; instead, it stores the real-time acquired data in the processor's internal storage unit for later processing. For data with relatively simple processing and analysis, the processor's functionality can be expanded to directly output the processed data to the external system. If the data volume is too large, the imaging system's transmission capabilities can be expanded by adding a wireless transmission module to wirelessly transmit the real-time acquired information back to the ground terminal, achieving real-time observation.

[0122] Based on the above working principle, the following describes the application scenarios of UAV-borne hyperspectral imaging and details an implementation scheme of the imaging system described in this invention:

[0123] After the target image passes through the imaging lens, it is focused on the slit, which is the front window through which the target image enters the imaging spectrometer. Under software control, the motor moves according to a specific step size (or speed), ultimately stitching together lines of data to form a complete two-dimensional array display image. During this data acquisition process, the light intensity acquisition module collects light intensity information, which is simultaneously moved along with the relative displacement between the imaging spectrometer slit and the imaging lens. This light intensity information is also dispersed by the grating to form monochromatic light of different wavelengths, which is then recorded on the array detector. In other words, while scanning and imaging the ground target, the irradiance information of the ground target or the ambient light of its environment is also recorded. The purpose of this ambient light is to correct the irradiance value of each pixel in the slit scanning area to restore the true brightness value of each pixel, allowing the target attributes to be quantified in quantitative units.

[0124] The imaging lens push-broom acquisition imaging design is designed so that the action time of one lens push-broom imaging is about 10 seconds. This allows the motor to drive the imaging lens to move from the starting position until it completes a 1cm movement. At this time, the entire UAV-borne system is in a hovering state in the air, and the gimbal matched with the camera will correct its attitude in real time, so that the built-in push-broom imaging is in a relatively stable state, thus obtaining a hyperspectral image with very high accuracy.

[0125] After completing one cycle of data acquisition, the drone will move to the next hovering point and repeat the above actions. Generally, depending on the required flight altitude, the drone-borne system can acquire images from more than 20 points. Furthermore, the data acquisition from each hovering point overlaps with its adjacent points by approximately 25%. This overlap is intended to stitch together the image data from more than 20 independent points to achieve large-area image display, laying the groundwork for subsequent data processing and analysis.

[0126] The imaging system and imaging scheme described in this invention have the following advantages:

[0127] 1. The chlorophyll fluorescence imaging system based on the transmission imaging principle described in this invention adopts a non-prism imaging method. In this mode, the angle of dispersion of the monochromatic light output by the grating will be large, forming structural irregularities and eliminating the existence of ghost images.

[0128] 2. The chlorophyll fluorescence imaging system based on the transmission imaging principle described in this invention can achieve signal detection in the 650nm-800nm ​​spectral range, and at the same time, it can obtain fluorescence images with high spectral resolution, high spatial resolution, and high signal-to-noise ratio.

[0129] 3. The chlorophyll fluorescence imaging system based on the transmission imaging principle described in this invention adopts a lens scanning imaging method and is a fluorescence hyperspectral imaging system that integrates acquisition, control, real-time data calibration and processing.

[0130] 4. The chlorophyll fluorescence imaging system based on the transmission imaging principle described in this invention can achieve synchronization of uplink and downlink information through a unique light intensity collection and acquisition method, which not only ensures the independence of the beam splitting path, but also achieves a high degree of system consistency.

[0131] 5. When the chlorophyll fluorescence imaging system based on the transmission imaging principle described in this invention is combined with UAV-borne technology, the field of view can be larger, multiple areas can be photographed in one flight, and the transmission imaging structure can have high light transmission efficiency, thus providing higher efficiency for fluorescence imaging.

[0132] In summary, the imaging system provided by this invention addresses technical bottlenecks from multiple dimensions, from optical principle design to imaging structure formation and systematic output, achieving specific spectral and image acquisition methods for specific targets. Based on an independently developed lens push-broom imaging method, it ensures high-quality and accurate output results. Simultaneously, combined with real-time ambient light intensity acquisition technology, it enables quantitative analysis of research objects, expanding beyond the traditional model of qualitative research followed by quantitative analysis. This provides a more comprehensive sunlight-induced chlorophyll fluorescence imaging solution based on hyperspectral imaging technology for vegetation remote sensing, offering a more intuitive and efficient observation platform for applications such as environmental monitoring, carbon emissions, crop pests and diseases, crop breeding, health status assessment, yield prediction, and plant photosynthesis.

[0133] It is understood that the above detailed description of the present invention is for illustrative purposes only and is not intended to limit the technical solutions described in the embodiments of the present invention. Those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention to achieve the same technical effects; as long as the usage requirements are met, they are all within the protection scope of the present invention.

Claims

1. A chlorophyll fluorescence imaging system, characterized by, Includes the housing, imaging lens, moving components, and processor; A mounting hole is provided on one side wall of the housing; The imaging lens is mounted on the movable component and extends out of the housing through a mounting hole, the width of which is greater than the width of the imaging lens. The movable component is located inside the housing and is used to drive the imaging lens to move laterally along the mounting hole; The housing contains, in sequence from the self-imaging lens, a slit, a first lens group, a grating, a second lens group, and an area array detector; A light intensity acquisition module for acquiring the light intensity of a light source is provided on one side of the slit of the slit plate; The slit and the first lens group are both arranged parallel to the imaging lens; The grating is not parallel to the first lens group; The second lens group is not parallel to the grating, and the second lens group is not parallel to the first lens group; The optical path formed by the imaging lens, slit, light intensity acquisition module, first lens group, grating, second lens group and area array detector is enclosed in a housing; The processor is housed inside the casing and is electrically connected to the moving components and the area array detector. An electronic interface for outputting data is installed on the outer wall of the casing, and the electronic interface is electrically connected to the processor.

2. The chlorophyll fluorescence imaging system of claim 1, wherein, The light intensity acquisition module is made of optical fiber.

3. The chlorophyll fluorescence imaging system of claim 1, wherein, The moving component includes a motor, a lead screw, and a connecting block. The motor is installed inside the housing and its output shaft is fixedly connected to one end of the lead screw. The mounting part of the imaging lens is fixedly connected to the lead screw nut on the lead screw via the connecting block. The motor is controlled by a processor.

4. The chlorophyll fluorescence imaging system of claim 1, wherein, The mounting hole is provided with a telescopic dustproof baffle.

5. The chlorophyll fluorescence imaging system of claim 1, wherein, It also includes an auxiliary camera, which is mounted on one side of the imaging lens and is used to monitor the field of view of the imaging lens. The auxiliary camera is electrically connected to the processor.

6. The chlorophyll fluorescence imaging system of claim 1, wherein, The casing is provided with a heat dissipation structure.

7. The chlorophyll fluorescence imaging system of claim 6, wherein, It also includes a fan located inside the casing.

8. The imaging method of the chlorophyll fluorescence imaging system according to claim 1, specifically comprising: The processor controls the movement of the moving components; The imaging lens moves according to a predetermined stroke under the drive of the moving component to perform push-broom acquisition of the target under test; The target image is focused by the imaging lens and then imaged on the slit. After collimation by the first lens group, grating dispersion, and second lens group, the image of the target image is output to the area array detector. The light intensity acquisition module simultaneously acquires the light intensity of the light source, and outputs the light intensity image to the area array detector after passing through slit imaging, collimation of the first lens group, grating dispersion, and collimation of the second lens group. The processor receives and stores the output information of the area array detector, and outputs the output information of the area array detector to the outside of the imaging system through an electronic interface.

9. The imaging method of the chlorophyll fluorescence imaging system according to claim 5, specifically comprising: The auxiliary camera monitors the field of view of the imaging lens in real time and feeds the field of view information back to the processor; The processor controls the movement of the moving components; The imaging lens moves according to a predetermined stroke under the drive of the moving component to perform push-broom acquisition of the target under test; The target image is focused by the imaging lens and then imaged on the slit. After collimation by the first lens group, grating dispersion, and second lens group, the image of the target image is output to the area array detector. The light intensity acquisition module simultaneously acquires the light intensity of the light source, and outputs the light intensity image to the area array detector after passing through slit imaging, collimation of the first lens group, grating dispersion, and collimation of the second lens group. The processor receives and stores the output information of the array detector and the auxiliary camera, and outputs this output information to the outside of the imaging system through an electronic interface.

10. An unmanned aerial chlorophyll fluorescence imaging system, comprising: The chlorophyll fluorescence imaging system comprising any one of claims 1 to 7 is mounted on a drone.

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