Snapshot sunlight-induced chlorophyll fluorescence imaging method and system

Abstract

The invention discloses a snapshot type sunlight-induced chlorophyll fluorescence imaging method and system. The method comprises the following steps: acquiring images of a plant to be detected and a reflecting plate by adopting a CCD (Charge Coupled Device) camera; three kinds of adjustable narrow-band optical filters are arranged between the lens and a sensor of the CCD camera. When the optical filter rotating wheel is rotated, the lens of the CCD camera is aligned with and shoots the plant to be detected and the reflecting plate under the three narrow-band optical filters; filtering wavelengths of the three narrow-band filters are used as wavelength values inside and outside an oxygen absorption line, and pixel brightness of a pixel where a reflecting plate is located in a picture shot by a CCD (Charge Coupled Device) camera under each narrow-band filter is used as solar irradiance spectral intensity in the absorption line. And taking the pixel brightness of the pixel of the plant to be detected in the picture as the radiance spectral intensity reflected by the vegetation canopy, and obtaining a sunlight-induced chlorophyll fluorescence signal and a fluorescence image under each pixel in combination with a 3FLD algorithm, thereby facilitating tracing analysis of sunlight-induced chlorophyll fluorescence.

Description

Technical Field

[0001] The present invention relates to the technical field of remote sensing of solar-induced chlorophyll fluorescence, and specifically to a snapshot solar-induced chlorophyll fluorescence imaging method and system. Background Art

[0002] Solar-induced chlorophyll fluorescence, also known as SIF, is a by-product of photosynthesis and contains rich photosynthesis information. By observing solar-induced chlorophyll fluorescence information, it helps us better understand the process and efficiency of photosynthesis. Relevant research shows that solar-induced chlorophyll fluorescence is directly related to the gross primary productivity GPP of the ecosystem. With the support of China's "dual carbon" policy background, analyzing solar-induced chlorophyll fluorescence helps us further study the carbon sink-related data of the ecosystem.

[0003] The inversion values of solar-induced chlorophyll fluorescence may also vary significantly due to factors such as terrain, light, and moisture. This indicates the limitations of non-imaging spectrometers in monitoring solar-induced chlorophyll fluorescence. When facing large or complex vegetation areas, the measurement representativeness is often limited, and it is difficult to conduct traceability analysis of solar-induced chlorophyll fluorescence. For example, in the paper "Research on Hyperspectral Imager for Vegetation Solar-Induced Chlorophyll Fluorescence", it can be seen from the effect diagrams of this paper that even in areas with close distances, the inversion values of solar-induced chlorophyll fluorescence may vary significantly due to factors such as terrain, light, and moisture. Traditional non-imaging spectral systems can only invert a single solar-induced chlorophyll fluorescence value for a small area, that is, only obtain the total value of solar-induced chlorophyll fluorescence in this area, but do not know which plants or environmental factors specifically affect these fluorescences. That is, it is difficult to conduct traceability analysis of solar-induced chlorophyll fluorescence, which is not conducive to targeted governance of different ecological environments.

[0004] Existing solar-induced chlorophyll fluorescence monitoring systems are represented by the large-scale overall measurement of traditional spectrometers combined with fiber optic cosine correctors. These systems are all non-imaging systems and can only obtain one-dimensional spectral information for the orientation and field of view of the optical fiber, without including image and depth information. Although there are already some imaging spectrometers on the market that can be used for imaging spectral measurement of solar-induced chlorophyll fluorescence, these spectrometers are generally push-broom or point-scan imaging spectrometers for airborne or satellite scenarios. The instrument and measurement costs are relatively high, and the required measurement time is relatively long. It may not be possible to achieve stable measurement in environments with rapid changes in light conditions such as cloudy or overcast days. This will limit the further utilization of solar-induced chlorophyll fluorescence data.

[0005] The invention patent application with the patent publication number CN116106280A discloses a three-dimensional chlorophyll fluorescence imaging system for plants based on structured light vision. The method includes: building a three-dimensional chlorophyll fluorescence imaging system; switching the measuring light source, actinic light source, saturating pulse light source, and far-red light source in the red filter mode, and collecting chlorophyll fluorescence images of plants in different states; turning on the ordinary white light source, and sequentially collecting single-channel images of the plant in the red, green, and blue filter modes, and fusing them to obtain a three-channel color image of the plant; turning off all light sources, and collecting the double-frequency twelve-step phase-shift fringe image modulated by the plant in the neutral filter mode, and reconstructing the three-dimensional point cloud model of the plant; using the chlorophyll fluorescence image and the three-channel color image to perform per-pixel rendering on the three-dimensional point cloud model of the plant to achieve three-dimensional chlorophyll fluorescence imaging of the plant. However, this system belongs to the field of laser-induced chlorophyll fluorescence, which is different from sunlight-induced chlorophyll fluorescence. In order to avoid the interference of ambient light, laser-induced chlorophyll fluorescence is usually tested in a dark room or a low-light environment, which also makes it possible to use a streak camera to build a plant model in this patent. However, in an outdoor environment, the fringe information is difficult to distinguish under strong light, and if the target object is too far away, the deformation of the fringe pattern may not be obvious, resulting in a decrease in accuracy, which causes the three-dimensional modeling method of the streak camera to be inapplicable to sunlight-induced chlorophyll fluorescence imaging. Laser-induced chlorophyll fluorescence is generally used to provide relatively clear chlorophyll fluorescence characteristics, while sunlight-induced chlorophyll fluorescence is more used for large-scale ecological monitoring and crop health assessment. For laser-induced chlorophyll fluorescence, the excitation source is a laser, usually a monochromatic light with strong wavelength selectivity. And the light energy of the laser is relatively high, which can provide a directional and stable excitation light source, making the fluorescence signal stronger and clearer. The fluorescence signal induced by sunlight is weak and is easily affected by various factors such as ambient light, leaf health status, and vegetation type. The signal of sunlight-induced chlorophyll fluorescence is more difficult to accurately measure than that of laser-induced chlorophyll fluorescence, requires high-sensitivity instruments, and the measurement is limited by the changes of natural light. Usually, remote sensing technology or space satellites are used to measure sunlight-induced chlorophyll fluorescence in large areas.

[0006] The invention patent application with the patent publication number CN119091190A discloses a method and an imaging system for sunlight-induced chlorophyll fluorescence multispectral imaging. In this patent, a system using a CCD camera and a filter with a target wavelength is used to obtain chlorophyll fluorescence information. When calculating the fluorescence, only the linear correspondence between the light intensity of the calibration light source in the target band and the light intensity of the photographed vegetation in the target band is directly used as the intensity of sunlight-induced chlorophyll fluorescence. This method cannot obtain the specific and accurate value of sunlight-induced chlorophyll fluorescence, cannot be compared and verified with other sunlight-induced chlorophyll fluorescence systems, and only using the light intensity value at one wavelength cannot deduce the specific value of sunlight-induced chlorophyll fluorescence. Summary of the Invention

[0007] The technical problem to be solved by the present invention is as follows: for outdoor scenes, the one-dimensional spectral information measured by the traditional non-imaging spectral system for the observation of the range of solar-induced chlorophyll fluorescence has limited representativeness in the measurement of large vegetation areas or complex vegetation areas, and it is difficult to conduct traceability analysis of solar-induced chlorophyll fluorescence.

[0008] To solve the above technical problems, the present invention provides the following technical solutions: A snapshot solar-induced chlorophyll fluorescence imaging method, comprising: S10, using a CCD camera to acquire images of the plant to be measured and a reflector; three adjustable narrow-band filters are provided between the lens and the sensor of the CCD camera; S20, aligning the center of one of the narrow-band filters perpendicular to the principal optical axis of the CCD camera; the CCD camera takes pictures of the plant to be measured and the reflector; S30, repeating step S20 to obtain images of the plant to be measured and the reflector taken by the CCD camera under the remaining two narrow-band filters; S40, taking the filtering wavelengths of the three narrow-band filters as the wavelength values inside and outside the oxygen absorption line, taking the pixel brightness of the pixels where the reflector is located in the images taken by the CCD camera under each narrow-band filter as the spectral intensity of the solar irradiance inside the absorption line, taking the pixel brightness of the pixels where the plant to be measured is located in the photo as the spectral intensity of the radiance reflected by the vegetation canopy, and combining with the three-channel Fraunhofer line depth method to obtain the solar-induced chlorophyll fluorescence signal under each pixel; S50, calculating the solar-induced chlorophyll fluorescence signals under all pixels in the same way as obtaining the solar-induced chlorophyll fluorescence signals under each pixel in step S40 to obtain a fluorescence image.

[0009] Technical effect: The present invention can expand the angle of solar-induced chlorophyll fluorescence observation from one-dimensional to two-dimensional, which is more conducive to analyzing the differences in solar-induced chlorophyll fluorescence generated at different positions of the measured plants or different measured plants, filling the gap in SIF imaging monitoring from the laboratory leaf scale to the satellite and airborne remote sensing scales.

[0010] In an embodiment of the present invention, the filtering wavelengths of the three narrow-band filters are respectively 757 nm, 761 nm and 770 nm.

[0011] In an embodiment of the present invention, the full width at half maximum of each narrow-band filter is 1.2 - 1 nm.

[0012] In an embodiment of the present invention, the lens of the CCD camera meets the standard of an image-space telecentric lens.

[0013] In an embodiment of the present invention, multiple reflection films with different reflectivities are provided on the reflector, and the reflection films meet the reference standard of a diffuse reflection target board.

[0014] In an embodiment of the present invention, before the CCD camera photographs the plant to be measured and the reflector, the CCD camera is first initialized and calibrated: The CCD camera is directed at the standard light source for photographing, and the image parameters of the CCD camera are adjusted to make the brightness of the photographed standard light source image uniform; the image parameters of the CCD camera under the condition of uniform brightness of the standard light source image are retained; Using the image parameters during the initialization and calibration of the CCD camera, photograph the plant to be measured and the reflector under three narrow-band filters; Under the application of the three-channel Fraunhofer line depth method, correct the photos of the plant to be measured and the reflector under three narrow-band filters: Through the reflectivity of each reflective film on the reflector, correct the brightness of the entire picture to make the response curve of each pixel linear after the CCD camera passes through the narrow-band filter.

[0015] In an embodiment of the present invention, the solar-induced chlorophyll fluorescence signal at each pixel is obtained , through the following formula: ; ; ; In the formula, , , respectively represent the left wavelength band of the oxygen absorption line, the oxygen absorption line, and the right wavelength band of the oxygen absorption line, which are the filter wavelengths of the narrow-band filter, , respectively represent the weights of the left and right wavelength bands of the oxygen absorption line, , respectively represent the pixel brightness of the pixel where the reflector is located and the pixel brightness of the pixel where the plant to be measured is located at the wavelength of the narrow-band filter representing the oxygen absorption line, , respectively represent the pixel brightness of the pixel where the reflector is located and the pixel brightness of the pixel where the plant to be measured is located at the wavelength of the narrow-band filter representing the left wavelength band of the oxygen absorption line, , respectively represent the pixel brightness of the pixel where the reflector is located and the pixel brightness of the pixel where the plant to be measured is located at the wavelength of the narrow-band filter representing the right wavelength band of the oxygen absorption line.

[0016] In an embodiment of the present invention, the snapshot solar-induced chlorophyll fluorescence imaging method further includes: S60, remove the adjustable filter wheel and the reflector, set two single CCD cameras to form a binocular CCD camera; set the lidar; S70, A binocular CCD camera captures the plant to be measured, and the SGBM algorithm using parallax analysis is utilized to obtain a two-dimensional depth information map of the plant to be measured; a lidar acquires the three-dimensional point cloud data of the plant to be measured; S80, First, the two-dimensional depth information map is corrected by the three-dimensional point cloud data to obtain three-dimensional point cloud data with depth information, and then the point cloud is colored according to the two-dimensional distribution value of the fluorescence image to obtain a three-dimensional daylight-induced chlorophyll fluorescence image.

[0017] Technical effect: When two-dimensional imaging faces ecological structures with obvious structural features such as trees and forests, spectral measurement errors may be caused by structural changes. Combining the binocular vision of the binocular CCD camera and the lidar ranging technology as a supplement and improvement is beneficial for comparing and correcting fluorescence test errors, and analyzing the growth trend of plants, the influence of the three-dimensional structural information of the plant canopy structure and other ecosystems on the daylight-induced chlorophyll fluorescence information.

[0018] In an embodiment of the present invention, the snapshot daylight-induced chlorophyll fluorescence imaging method further includes: A lidar is set up to obtain the three-dimensional point cloud data of the plant to be measured through the lidar, and then the two-dimensional distribution value of the fluorescence image is used to color the point cloud to obtain a three-dimensional plant daylight-induced chlorophyll fluorescence modeling image.

[0019] The present invention also provides a snapshot daylight-induced chlorophyll fluorescence imaging system, which applies the above-mentioned snapshot daylight-induced chlorophyll fluorescence imaging method, including: A hardware module for using a CCD camera to acquire images of the plant to be measured and a reflector; three adjustable narrow-band filters are arranged between the lens and the sensor of the CCD camera; A shooting module for selecting the center of one of the narrow-band filters to be vertically aligned with the principal optical axis of the CCD camera; the CCD camera shoots the plant to be measured and the reflector; this step is repeated to obtain images of the plant to be measured and the reflector taken by the CCD camera under the remaining two narrow-band filters; An inversion module for using the filter wavelengths of the three narrow-band filters as the wavelength values inside and outside the oxygen absorption line, taking the pixel brightness of the reflector in the image taken by the CCD camera under each narrow-band filter as the solar irradiance spectral intensity inside the absorption line, taking the pixel brightness of the plant to be measured in the photo as the radiance spectral intensity reflected by the vegetation canopy, and combining the three-channel Fraunhofer line depth method to obtain the daylight-induced chlorophyll fluorescence signal at each pixel; An imaging module for calculating the daylight-induced chlorophyll fluorescence signals at all pixels in the same way as the inversion module to obtain the fluorescence image.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: For the traditional observation of the range of solar-induced chlorophyll fluorescence using a spectrometer and optical fibers, snapshot solar-induced chlorophyll fluorescence imaging can expand the observation angle from one-dimensional to two-dimensional, which is more conducive to analyzing the differences in solar-induced chlorophyll fluorescence generated at different positions of plants or different plants. At the same time, compared with push-broom or point-scanning spectrometers on airborne and satellite platforms, it has faster imaging speed, more flexible use, and lower cost.

[0021] The binocular CCD camera-lidar solution can perform three-dimensional point cloud modeling of plants. While performing two-dimensional solar-induced chlorophyll fluorescence analysis of plants, by analyzing plant phenotypes and structures, it can further analyze the growth level of plants and the influence of the structure of the plant canopy on the measurement of solar-induced chlorophyll fluorescence in the actual ecosystem. The binocular CCD camera and lidar can complement each other. The lidar makes up for the disadvantages of the binocular CCD camera in terms of insufficient ranging distance and low accuracy, and the binocular CCD camera makes up for the disadvantages of the lidar in terms of low pixel density and difficulty in classifying and identifying plants, and can also make up for the ranging blind area of the lidar at close range. The combined snapshot solar-induced chlorophyll fluorescence three-dimensional imaging spectroscopy system can flexibly analyze the three-dimensional spatial characteristics of solar-induced chlorophyll fluorescence under different conditions.

[0022] Different from the prior art that uses active light sources such as lasers to measure chlorophyll fluorescence in a dark room or dark box, the present invention belongs to passive measurement. For the first time, the 3FLD fluorescence inversion method based on ultra-narrowband filters is used in the field of solar-induced chlorophyll fluorescence imaging. It can be used for actual outdoor observation. By using a CCD camera combined with three narrowband filters to replace the fiber optic spectrometer and scanning imaging spectrometer, the radiance of the entire image in a single band can be obtained with only a single shot. By switching the filters through an electric filter wheel, all the radiance information required for inverting solar-induced chlorophyll fluorescence by the 3FLD method can be obtained through multiple shots.

[0023] The CCD camera has a good linear response to the radiation intensity compared with the CMOS camera, which can improve the accuracy of inversion. The 16-bit CCD sensor has extremely high sensitivity and can accurately capture weak fluorescence intensity changes.

[0024] Use a filter wheel in combination with a CCD camera, and control the filter wheel through a computer to switch the measurement spectral range.

[0025] For the first time, ultra-narrowband filters are used in solar-induced chlorophyll fluorescence imaging. The wavelengths of the ultra-narrowband filters are located at 757 nm, 761 nm, and 770 nm, covering the O2-A band required for inverting solar-induced chlorophyll fluorescence, and the full width at half maximum is only 1.2 nm, which can accurately capture fluorescence intensity changes.

[0026] The reflector is engraved with an optical reflection film with different reflectivities, which is used to measure and correct the downward solar radiation. Innovatively, while shooting the intensity information of the reflected light of the vegetation, the intensity of the solar radiation is recorded, which simplifies the recording steps of the upward and downward light intensities.

[0027] For the first time, a binocular CCD camera and a lidar system are introduced into the outdoor observation of solar-induced chlorophyll fluorescence imaging, which provides the possibility for three-dimensional analysis of solar-induced chlorophyll fluorescence. Brief Description of the Drawings

[0028] Figure 1 It is a flowchart of a snapshot solar-induced chlorophyll fluorescence imaging method according to an embodiment of the present invention.

[0029] Figure 2 It is a schematic diagram of snapshot solar-induced chlorophyll fluorescence imaging in Embodiment 1 according to an embodiment of the present invention.

[0030] Figure 3 It is a schematic diagram of snapshot solar-induced chlorophyll fluorescence imaging in Embodiment 2 according to an embodiment of the present invention.

[0031] Figure 4 It is a schematic diagram of snapshot solar-induced chlorophyll fluorescence imaging in Embodiment 3 according to an embodiment of the present invention.

[0032] Figure 5 It is a system block diagram of a snapshot solar-induced chlorophyll fluorescence imaging method according to an embodiment of the present invention. Detailed Embodiments

[0033] To facilitate the understanding of the technical solution of the present invention by those skilled in the art, the technical solution of the present invention will be further described below with reference to the accompanying drawings of the specification.

[0034] The terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present application, "a plurality" means two or more unless otherwise specifically defined.

[0035] Embodiment 1 Please refer to Figure 1 and Figure 2 As shown, the present invention provides a snapshot solar-induced chlorophyll fluorescence imaging method, including S10, using a CCD camera to obtain images of the plant to be measured and the reflector; three adjustable narrow-band filters are provided between the lens and the sensor of the CCD camera.

[0036] In an embodiment of the present invention, the plant A to be measured may be vegetation, tree canopy, paddy field, etc.

[0037] In this embodiment, for solar-induced chlorophyll fluorescence, it is necessary to measure the solar intensity and the plant reflected light intensity as simultaneously as possible. If the measurements are carried out separately, it may cause a time difference and lead to inaccurate fluorescence measurement. Placing the reflector 10 near the plant A to be measured provides a feasible solution for simultaneously measuring the solar intensity and the plant reflected light intensity.

[0038] In this embodiment, the reflector 10 is located beside the plant A to be measured. When the CCD camera 20 captures the reflection intensity of the plant A to be measured, it also records the downward solar radiation intensity measurement. The positional relationship of the reflector 10 is required to be as close as possible to the plant A to be measured so that the two can be captured by the lens 21 simultaneously. The purpose of the reflector 10 is to record the essential solar information in the measurement of solar-induced chlorophyll fluorescence.

[0039] In this embodiment, multiple reflecting films 11 with different reflectivities are provided on the reflector 10, and the reflecting films 11 meet the reference standards of a diffuse reflection target board. The reflection coefficients of the four reflecting films 11 are 90%, 50%, 20%, and 5% respectively. The four reflecting films 11 represent surfaces with different reflection capabilities, and their function is to provide different reflected light intensities to simulate the light reflection behaviors of different types of object surfaces in the actual environment.

[0040] In this embodiment, the CCD camera 20 has a good linear response to the radiation intensity compared with the CMOS camera, which can improve the accuracy of inversion. The 16-bit sensor 22 of the CCD camera 20 has extremely high sensitivity and can accurately capture weak fluorescence intensity changes.

[0041] In this embodiment, the lens optical path design of the imaging system meets the image-space telecentric optical path. By controlling the light to enter the sensor 22 of the CCD camera 20 at a perpendicular angle, it avoids the brightness attenuation caused by the marginal light incident on the sensor obliquely in the traditional lens, and also avoids the shift of the central wavelength and bandwidth of the filter caused by the large-angle light passing through the filter.

[0042] In this embodiment, the filter wavelengths of the three narrowband filters 31 on the filter wheel 30 are respectively set to 757 nm, 761 nm, and 770 nm, covering the O2-A band required for inverting solar-induced chlorophyll fluorescence. Specifically, the narrowband filter 31 is an ultra-narrowband filter for the following reasons: Under natural light conditions, the fluorescence emitted by vegetation accounts for only about 1% - 5% of the solar radiation reflected by vegetation, so it is a very weak optical signal. However, since there are many elemental gas substances evaporated from the sun in the solar atmosphere, when sunlight passes through the solar atmosphere, the light with the same spectral lines as these elemental substances in sunlight is absorbed, resulting in many dark lines with a bandwidth of 0.1 - 10 nm in the solar spectrum observed on the Earth's surface against the background of the continuous spectrum, namely Fraunhofer dark lines. At the same time, certain gases in the Earth's atmosphere, such as carbon dioxide, oxygen, and water vapor, etc., will also strongly absorb sunlight of specific wavelengths, forming atmospheric absorption dark lines. In the red and far-red bands, there are 3 relatively prominent dark lines: the Hα dark line formed by hydrogen absorption at 656 nm, and the O2-A and O2-B dark lines formed by the absorption of oxygen molecules in the Earth's atmosphere near 760 nm and 687 nm. In the bands of Fraunhofer dark lines and Earth's atmospheric absorption dark lines, vegetation absorbs photosynthetically active radiation for photosynthesis and emits SIF, filling a certain part of the dark line bands, thus producing an obvious filling effect. The technical method of SIF remote sensing is to compare the depth of the solar radiation spectral line with the depth of the plant radiation spectral line, and measure the degree to which the SIF from plants fills the dark lines. The SIF value is obtained by comparing the relative intensities of solar radiation and vegetation-reflected radiation at the dark lines and their adjacent spectral regions. Foreign scholars have proposed a three-band inversion method, the three-channel Fraunhofer line depth method (3FLD, Three-Band Fraunhofer Line Depth), which assumes that the reflectivity changes linearly within a very narrow band range, and uses the weighted average of the reflectivities of the two bands on the left and right of the absorption line to fit the reflectivity at the absorption point. Since an overly large filter bandwidth will cause the fluorescence signal to be mixed in the ambient light of other bands and be difficult to distinguish, a narrowband filter 31 needs to be set as an ultra-narrowband filter. Specifically, the full width at half maximum of each narrowband filter is 1.2 - 1 nm.

[0043] In this embodiment, current research shows that when the spectral resolution of the instrument is better than 1 nm and the signal-to-noise ratio is greater than 100:1, the observed data can be used for fluorescence inversion. However, the spectral resolution is also closely related to the signal-to-noise ratio and the observed band and shows an inverse relationship. Therefore, the spectral resolution cannot be increased without limit. According to the simulation experiment analysis, when the full width at half maximum of the narrowband filter, that is, the bandpass range, is about 1.2 nm, the measured fluorescence signal has a good agreement with that of a high-resolution spectrometer. Therefore, in this embodiment, three ultra-narrowband filters near 760 nm are selected, and the full width at half maximum of the narrowband filter is 1.2 nm to ensure capturing weak fluorescence signal changes. If the full width at half maximum of the narrowband filter 31 is larger, it means more ambient light enters, which is less conducive to separating the fluorescence signal.

[0044] S20. Select one of the narrowband filters and vertically align its center with the principal optical axis of the CCD camera; the CCD camera captures images of the plant to be measured and the reflector.

[0045] In this embodiment, the output shaft of the rotary motor 32 is connected to the filter wheel 30 to drive the rotation of the narrowband filter 31. The center of the narrowband filter 31 is vertically aligned with the principal optical axis of the CCD camera 20, avoiding changes in the transmittance characteristics that may be caused by machining errors or other reasons at the edge of the filter.

[0046] S30. Repeat step S20 to obtain images captured by the CCD camera of the plant to be measured and the reflector under the remaining two narrowband filters.

[0047] S40. Take the filter wavelengths of the three narrowband filters as the wavelength values inside and outside the oxygen absorption line. For each narrowband filter, take the pixel brightness of the pixels where the reflector is located in the image captured by the CCD camera as the spectral intensity of the solar irradiance inside the absorption line, and take the pixel brightness of the pixels where the plant to be measured is located in the photo as the spectral intensity of the radiance reflected by the vegetation canopy. Combine with the three-channel Fraunhofer line depth method to obtain the solar-induced chlorophyll fluorescence signal at each pixel.

[0048] In this embodiment, in the measurement of solar-induced chlorophyll fluorescence SIF, 3FLD is a spectral analysis method used to more accurately extract the solar-induced chlorophyll fluorescence signal from the reflection spectrum. However, the input data of the current 3FLD algorithm are all one-dimensional data measured by a non-imaging spectrometer. The specific formula is as follows: ; ; ; In the formula, , , are the wavelength values of the absorption line, the wavelength value of the left band of the absorption line, and the wavelength value of the right band of the absorption line respectively, , are the weight coefficients of the wavelength values of the left and right bands of the absorption line respectively, , are the spectral intensity of the solar irradiance inside the absorption line and the spectral intensity of the radiance reflected by the vegetation canopy respectively, , , , are the spectral intensity of the solar irradiance on the left and right of the absorption line and the spectral intensity of the radiance reflected by the vegetation canopy respectively, is the fluorescence signal retrieved under one-dimensional data.

[0049] The above shows that the 3FLD algorithm only requires the radiance intensity in several bands rather than the full-band continuous spectrum, which makes it possible to use the filter-based snapshot imaging spectroscopy technology for the inversion of solar-induced chlorophyll fluorescence imaging.

[0050] In this embodiment, the sensor 22 of the CCD camera has a good linear response to the change of light intensity, that is, the light intensity and the CCD electrical signal intensity change linearly. This shows that with the cooperation of an ultra-narrowband filter, only simple linear correction and certain angular correction are required to correspond the light intensity of a single band with the signal value of the sensor 22. This indicates that the electrical signal intensity of the photo can represent the light intensity of this band of the current narrowband filter. That is, the filter wavelengths of the three narrowband filters 31 can be used as the wavelength values inside and outside the oxygen absorption line. Under each narrowband filter, the pixel brightness of the pixel where the reflector is located in the photo taken by the CCD camera 20 is used as the spectral intensity of the solar irradiance inside the absorption line, and the pixel brightness of the pixel where the plant to be measured is located in the photo is used as the spectral intensity of the radiance reflected by the vegetation canopy.

[0051] In this embodiment, before the CCD camera 20 takes pictures of the plant to be measured and the reflector, the CCD camera 20 is first initialized and corrected: The CCD camera 20 is directed at a standard light source for shooting, and the image parameters of the CCD camera 20 are adjusted to make the brightness of the captured standard light source image uniform, and the image parameters of the CCD camera 20 under the condition of uniform brightness of the standard light source image are retained.

[0052] The image parameters during the initialization and correction of the CCD camera 20 are applied to take pictures of the plant to be measured and the reflector under the three narrowband filters 31.

[0053] In the application of the three-channel Fraunhofer line depth method, the photos of the plant to be measured and the reflector under the three narrowband filters 31 are corrected: Through the reflectivity of each reflection film 11 on the reflector 10, the brightness of the entire picture is corrected to make the response curve of each pixel linear after the CCD camera 20 passes through the narrowband filter 31.

[0054] Specifically, the solar-induced chlorophyll fluorescence signal at each pixel is obtained , through the following formula: ; ; ; In the formula, , , respectively represent the left band of the oxygen absorption line, the oxygen absorption line, and the right band of the oxygen absorption line, which are the filter wavelengths of the narrowband filter, , are the weights representing the left and right bands of the oxygen absorption line respectively, , are the pixel brightness of the pixel where the reflector is located and the pixel brightness of the pixel where the plant to be measured is located respectively at the wavelength of the narrowband filter representing the oxygen absorption line, , are the pixel brightness of the pixel where the reflector is located and the pixel brightness of the pixel where the plant to be measured is located respectively at the wavelength of the narrowband filter representing the left band of the oxygen absorption line, , are the pixel brightness of the pixel where the reflector is located and the pixel brightness of the pixel where the plant to be measured is located respectively at the wavelength of the narrowband filter representing the right band of the oxygen absorption line.

[0055] Specifically, it can be understood that in the formula, , , are the filter wavelengths of the narrowband filters at 757nm, 761nm and 770nm respectively, , are the weights of the filtering wavelengths at 757nm and 770nm, , are the pixel brightness of the pixel where the reflector is located and the pixel brightness of the pixel where the plant to be measured is located respectively under the narrowband filter at 761nm, , are the pixel brightness of the pixel where the reflector is located and the pixel brightness of the pixel where the plant to be measured is located respectively under the narrowband filter at 757nm, , are the pixel brightness of the pixel where the reflector is located and the pixel brightness of the pixel where the plant to be measured is located respectively under the narrowband filter at 770nm.

[0056] S50. Repeat the method of obtaining the solar-induced chlorophyll fluorescence signal at each pixel in step S40 to calculate the solar-induced chlorophyll fluorescence signals at all pixels and obtain a fluorescence image.

[0057] Embodiment 2 Please refer to Figure 3 as shown. The snapshot solar-induced chlorophyll fluorescence imaging method further includes: S60. Remove the adjustable filter wheel and the reflector, set two single CCD cameras to form a binocular CCD camera; set a lidar.

[0058] S70. The binocular CCD camera takes pictures of the plant to be measured, and uses the SGBM algorithm for disparity analysis to obtain a two-dimensional depth information map of the plant to be measured; the lidar obtains the three-dimensional point cloud data of the plant to be measured.

[0059] In this embodiment, the binocular camera system uses two CCD cameras 20 to shoot the same scene, obtaining two views, a left image and a right image, respectively. Since the positions of the two CCD cameras 20 are slightly different, the scene seen by each CCD camera 20 will have a slight parallax, that is, the position of the same object in the left image and the right image is slightly different. This position difference is called "parallax" and is related to the distance of the object. By analyzing the parallax, the depth of the object, that is, the distance from the camera, can be calculated. Given the intrinsic and extrinsic parameters of the two CCD cameras 20, that is, the focal length, baseline distance, etc. of the camera, the depth Z of the object, that is, the distance from the CCD camera 20, can be calculated by parallax. This relationship can be expressed by the following formula: ; Where, is the depth of the object, the distance from the CCD camera, is the focal length of the CCD camera, which is usually obtained through the internal calibration of the CCD camera. is the baseline distance between the CCD cameras, that is, the horizontal distance between the centers of the two CCD cameras, is the disparity, which represents the horizontal coordinate difference of the same object in the left and right images.

[0060] In this embodiment, the present invention does not improve upon the disparity analysis SGBM algorithm. Instead, it utilizes this algorithm to determine the distance between CCD camera 20 and the plant under test. This yields a 3D point cloud of the plant under test from the perspective of CCD camera 20. This essentially generates a 2D depth map. Both binocular CCD camera and LiDAR-CCD camera approaches offer advantages in obtaining 3D point clouds of the plant under test and can complement each other.

[0061] S80, first correct the two-dimensional depth information map using the three-dimensional point cloud data to obtain three-dimensional point cloud data with depth information, and then color the point cloud using the two-dimensional distribution value of the fluorescence image to obtain a three-dimensional sunlight-induced chlorophyll fluorescence image.

[0062] In this embodiment, the binocular CCD camera's ranging results are corrected by the laser radar 40 to calculate the depth information and structural information of the plant to be measured. The binocular CCD camera measures the distance to the plant to be measured and generates a two-dimensional depth information map. Unlike the laser radar 40, the disparity analysis SGBM algorithm is an image-based matching algorithm, which may produce some measurement blind spots or errors due to matching accuracy issues. This is particularly noticeable when measuring at long distances. The laser radar 40 can be used to rescan and measure these areas to obtain a more accurate three-dimensional point cloud image of the plant to be measured. Specifically, in this embodiment, the present invention is not limited to the method of multi-source data alignment.

[0063] Example 3 See alsoFigure 4 As shown, the snapshot-type solar-induced chlorophyll fluorescence imaging method further includes: setting a lidar 40, obtaining three-dimensional point cloud data of the plant to be measured through the lidar 40, and then staining the point cloud with the two-dimensional distribution values of the fluorescence image to obtain a three-dimensionalized solar-induced chlorophyll fluorescence modeling image of the plant.

[0064] In this embodiment, the three-dimensional point cloud data and the fluorescence image data are directly aligned to obtain a three-dimensionalized solar-induced chlorophyll fluorescence image, omitting the correction of the ranging results of the lidar 40 for the binocular CCD camera.

[0065] Embodiment 4 Please refer to Figure 5 As shown, the present invention also provides a snapshot-type solar-induced chlorophyll fluorescence imaging system, including: A hardware module for using a CCD camera to obtain images of the plant to be measured and a reflector; three adjustable narrow-band filters are provided between the lens and the sensor of the CCD camera.

[0066] A shooting module for selecting the center of one of the narrow-band filters to be vertically aligned with the principal optical axis of the CCD camera; the CCD camera shoots the plant to be measured and the reflector; repeating this step to obtain the images of the plant to be measured and the reflector taken by the CCD camera under the remaining two narrow-band filters.

[0067] An inversion module for using the filter wavelengths of the three narrow-band filters as the wavelength values inside and outside the oxygen absorption line, taking the pixel brightness of the pixels where the reflector is located in the images taken by the CCD camera under each narrow-band filter as the solar irradiance spectral intensity inside the absorption line, and taking the pixel brightness of the pixels where the plant to be measured is located in the photo as the radiance spectral intensity reflected by the vegetation canopy, and combining the three-channel Fraunhofer line depth method to obtain the solar-induced chlorophyll fluorescence signal at each pixel.

[0068] An imaging module for calculating the solar-induced chlorophyll fluorescence signals at all pixels in the same way as the inversion module obtains the solar-induced chlorophyll fluorescence signals at each pixel, and obtaining a fluorescence image.

[0069] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be encompassed by the present invention, and any reference signs in the claims should not be regarded as limiting the claims involved.

[0070] The above-described embodiments merely represent the implementation manners of the invention. The protection scope of the present invention is not limited to the above embodiments only. For those skilled in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all fall within the protection scope of the present invention.

Claims

1. A snapshot-type solar-induced chlorophyll fluorescence imaging method, characterized in that, Including: S10. Use a CCD camera to obtain images of the plant to be measured and the reflector; three adjustable narrow-band filters are arranged between the lens and the sensor of the CCD camera. S20. Align the center of one of the narrow-band filters perpendicular to the principal optical axis of the CCD camera; the CCD camera takes pictures of the plant to be measured and the reflector. S30. Repeat step S20 to obtain the images of the plant to be measured and the reflector taken by the CCD camera under the remaining two narrow-band filters. S40. Take the filter wavelengths of the three narrow-band filters as the wavelength values inside and outside the oxygen absorption line. For each narrow-band filter, take the pixel brightness of the pixel where the reflector is located in the image taken by the CCD camera as the spectral intensity of the solar irradiance inside the absorption line, and take the pixel brightness of the pixel where the plant to be measured is located in the photo as the spectral intensity of the radiance reflected by the vegetation canopy. Combine the three-channel Fraunhofer line depth method to obtain the sunlight-induced chlorophyll fluorescence signal at each pixel. S50. Calculate the sunlight-induced chlorophyll fluorescence signals at all pixels in the same way as obtaining the sunlight-induced chlorophyll fluorescence signal at each pixel in step S40 to obtain a fluorescence image.

2. The snapshot type solar-induced chlorophyll fluorescence imaging method according to claim 1, characterized in that, The filter wavelengths of the three narrow-band filters are respectively 757 nm, 761 nm, and 770 nm.

3. The snapshot-type solar-induced chlorophyll fluorescence imaging method according to claim 1, wherein The full width at half maximum of each narrow-band filter is 1.2 - 1 nm.

4. The snapshot-type solar-induced chlorophyll fluorescence imaging method according to claim 1, wherein The lens of the CCD camera meets the standard of an image-space telecentric lens.

5. The snapshot-type solar-induced chlorophyll fluorescence imaging method according to claim 1, characterized in that, Multiple reflection films with different reflectivities are arranged on the reflector, and the reflection film meets the reference standard of a diffuse reflection target board.

6. The snapshot type solar-induced chlorophyll fluorescence imaging method according to claim 4, characterized in that Before the CCD camera takes pictures of the plant to be measured and the reflector, first perform initialization calibration on the CCD camera: Point the CCD camera at a standard light source and take pictures, adjust the image parameters of the CCD camera to make the brightness of the taken standard light source image uniform; retain the image parameters of the CCD camera when the brightness of the standard light source image is uniform. Apply the image parameters during the initialization calibration of the CCD camera to take pictures of the plant to be measured and the reflector under the three narrow-band filters. Under the application of the three-channel Fraunhofer line depth method, correct the photos of the plant to be measured and the reflector under the three narrow-band filters: Correct the brightness of the entire picture through the reflectivity of each reflection film on the reflector to make the response curve of each pixel linear after the CCD camera passes through the narrow-band filter.

7. The snapshot-type solar-induced chlorophyll fluorescence imaging method according to claim 1, wherein Obtain the solar-induced chlorophyll fluorescence signal at each pixel , through the following formula: ； ； ； Wherein, , , respectively represent the left wavelength band of the oxygen absorption line, the oxygen absorption line, and the right wavelength band of the oxygen absorption line, which are the filter wavelengths of the narrowband filter; , respectively represent the weights of the left and right wavelength bands of the oxygen absorption line; , respectively represent the pixel brightness of the pixel where the reflector is located and the pixel brightness of the pixel where the plant to be measured is located at the wavelength of the narrowband filter representing the oxygen absorption line; , respectively represent the pixel brightness of the pixel where the reflector is located and the pixel brightness of the pixel where the plant to be measured is located at the wavelength of the narrowband filter representing the left wavelength band of the oxygen absorption line; , respectively represent the pixel brightness of the pixel where the reflector is located and the pixel brightness of the pixel where the plant to be measured is located at the wavelength of the narrowband filter representing the right wavelength band of the oxygen absorption line.

8. The snapshot-type solar-induced chlorophyll fluorescence imaging method according to claim 1, wherein The described snapshot sunlight-induced chlorophyll fluorescence imaging method further includes: S60. Remove the adjustable filter wheel and the reflector, set two single CCD cameras to form a binocular CCD camera; set a lidar. S70. The binocular CCD camera takes pictures of the plant to be measured, and uses the disparity analysis SGBM algorithm to obtain the two-dimensional depth information map of the plant to be measured; the lidar obtains the three-dimensional point cloud data of the plant to be measured. S80. First correct the two-dimensional depth information map through the three-dimensional point cloud data to obtain the three-dimensional point cloud data with depth information, and then color the point cloud according to the two-dimensional distribution value of the fluorescence image to obtain a three-dimensional sunlight-induced chlorophyll fluorescence image.

9. The snapshot-type solar-induced chlorophyll fluorescence imaging method according to claim 1, wherein The described snapshot sunlight-induced chlorophyll fluorescence imaging method further includes: A lidar is set up to obtain the three-dimensional point cloud data of the plant to be measured through the lidar. Then, the two-dimensional distribution values of the fluorescence image are used to stain the point cloud, and a three-dimensional plant solar-induced chlorophyll fluorescence modeling image is obtained.

10. A snapshot type solar-induced chlorophyll fluorescence imaging system, characterized in that, Applying the snapshot solar-induced chlorophyll fluorescence imaging method according to any one of claims 1-9, comprising: A hardware module for obtaining images of the plant to be measured and a reflector using a CCD camera; three adjustable narrow-band filters are provided between the lens and the sensor of the CCD camera; A shooting module for selecting the center of one of the narrow-band filters to be vertically aligned with the principal optical axis of the CCD camera; the CCD camera shoots the plant to be measured and the reflector; repeating this step to obtain the images of the plant to be measured and the reflector taken by the CCD camera under the remaining two narrow-band filters; An inversion module for using the filter wavelengths of the three narrow-band filters as the wavelength values inside and outside the oxygen absorption line, using the pixel brightness of the pixels where the reflector is located in the images taken by the CCD camera under each narrow-band filter as the spectral intensity of the solar irradiance inside the absorption line, and using the pixel brightness of the pixels where the plant to be measured is located in the photo as the spectral intensity of the radiance reflected by the vegetation canopy, and combining the three-channel Fraunhofer line depth method to obtain the solar-induced chlorophyll fluorescence signal at each pixel; An imaging module for calculating the solar-induced chlorophyll fluorescence signals at all pixels in the same way as the inversion module obtains the solar-induced chlorophyll fluorescence signals at each pixel, and obtaining a fluorescence image.

Images