A method for retrieving chlorophyll content of plant leaves based on radiance

Abstract

The present application relates to a kind of plant leaf chlorophyll inversion methods based on radiance, comprising: S1, the radiance value of plant leaf in different wave band is measured;S2, according to the proportion of different wave band solar irradiance in solar incident radiation, the correction coefficient for traditional reflectivity ground chlorophyll index is calculated;S3, based on the correction coefficient, the correction coefficient ground chlorophyll index based on radiance is constructed by correcting traditional reflectivity ground chlorophyll index;S4, the regression model between the correction coefficient and chlorophyll is constructed;S5, based on the correction coefficient and the regression model constructed inversion chlorophyll.The present application directly calculates a kind of ground chlorophyll index based on radiance, realizes directly from radiance inversion plant leaf chlorophyll content.

Description

Technical Field

[0001] This invention relates to plant leaf chlorophyll inversion technology, and more specifically, to a method for plant leaf chlorophyll inversion based on radiance. Background Technology

[0002] In the chlorophyll retrieval of plant leaves, algorithms based on remote sensing data products are widely used. In these algorithms, calculating a pre-designed vegetation index using remote sensing data products is a necessary step in the retrieval process. Among these, the ground chlorophyll index is widely used because its retrieval results are often better than other common vegetation indices. Existing methods for calculating remote sensing vegetation indices primarily involve calculating the reflectance from different remote sensing data products to obtain the relevant vegetation index, and then using this index to retrieve plant leaf chlorophyll.

[0003] However, current technology lacks a method for directly using the radiance of remote sensing data products to retrieve chlorophyll in plant leaves. The difficulty lies in the fact that the leaf reflectance received by the sensor is affected by the incident radiance during measurement. Directly calculating the ground chlorophyll index using radiance performs poorly in retrieving plant leaf chlorophyll, making accurate chlorophyll retrieval difficult. On the other hand, its advantage lies in the fact that plant reflectance can be directly acquired using remote sensing sensors (near-infrared spectrophotometers, infrared cameras, etc.), while obtaining reflectance is relatively complex and often requires auxiliary equipment such as whiteboards. Summary of the Invention

[0004] The leaf reflectance received by remote sensing sensors is directly affected by the incident radiance. Therefore, compared to reflectance, radiance cannot stably reflect the leaf condition. To address the problems of existing technologies, this invention proposes a method for chlorophyll retrieval from plant leaves based on radiance, comprising: S1, measuring the radiance values ​​of plant leaves in different wavelength bands; S2, calculating a correction coefficient for the traditional reflectance ground chlorophyll index based on the proportion of solar radiance in different wavelength bands of incident solar radiation; S3, constructing a ground chlorophyll index based on radiance using the correction coefficient and by correcting the traditional reflectance ground chlorophyll index; S4, constructing a regression model between the correction coefficient and chlorophyll; and S5, retrieving chlorophyll based on the correction coefficient and the constructed regression model.

[0005] The technical effects of this invention include:

[0006] 1. The method of the present invention can directly calculate the ground chlorophyll index based on radiance.

[0007] 2. This invention proposes to use the 6S (Second Simulation of the Satellite Signal in the Solar Spectrum) radiative transfer model to simulate and calculate the ratio of incident radiance between bands under various atmospheric conditions, in order to correct the traditional ground chlorophyll index based on reflectivity.

[0008] 3. Since the reflectance data from remote sensing products is no longer needed in the calculation, more convenient equipment can be used to obtain the reflectance radiance data of plants.

[0009] 4. This invention does not require the use of whiteboards or other equipment to assist in calculating reflectance.

[0010] 5. The present invention uses radiance to calculate the ground chlorophyll index, which is simple to calculate, practical, and easy to apply and promote.

[0011] Furthermore, the method of the present invention is not limited to remote sensing sensors. With the popularization of portable remote sensing devices (such as smartphone cameras), it is also possible to directly acquire the radiance data of plant leaves and perform chlorophyll inversion of plant leaves through the corrected ground chlorophyll index based on radiance.

[0012] The present invention proposes a correction to the traditional ground chlorophyll index based on reflectance. By using the 6S radiative transfer model, a correction coefficient for radiance is designed and calculated. This coefficient can remain fixed in subsequent use and does not need to be recalculated. Attached Figure Description

[0013] To facilitate understanding of the invention, it will be described in more detail with reference to the specific embodiments shown in the accompanying drawings. These drawings depict only typical embodiments of the invention and should not be considered as limiting the scope of protection of the invention.

[0014] Figure 1 This is a flowchart of the method of the present invention. Detailed Implementation

[0015] The embodiments of the present invention are described below with reference to the accompanying drawings to enable those skilled in the art to better understand and implement the present invention. However, the listed embodiments are not intended to limit the present invention. In the absence of conflict, the following embodiments and the technical features in the embodiments can be combined with each other, wherein the same components are indicated by the same reference numerals.

[0016] like Figure 1 As shown, the method of the present invention includes S1-S5.

[0017] S1 measures the radiance of plant leaves in different wavelength bands.

[0018] In one instance, the radiance values ​​of plant leaves were measured at 750 nm, 710 nm, and 680 nm wavelengths.

[0019] The ground chlorophyll index is widely used because its inversion effect is often better than other common vegetation indices. Its calculation formula is shown in formula (4) below, which uses the three bands of 750nm, 710nm and 680nm. In the embodiments of the present invention, a new ground chlorophyll index based on radiance is calculated after introducing a correction coefficient based on the vegetation index. Therefore, these three relevant bands are selected for measurement.

[0020] S2, calculates the correction coefficient for the traditional reflectivity ground chlorophyll index based on the proportion of solar irradiance in different bands of solar incident radiation.

[0021] In one embodiment, correction factors a and b for 750nm versus 680nm and 710nm versus 680nm are simulated under various conditions, and their values ​​are ultimately determined. These correction factors can remain fixed in subsequent use and do not need to be recalculated.

[0022] Models simulating atmospheric radiative transfer processes can be used to calculate correction coefficients; for example, LESS and Modtran models can be used for data simulation. Preferably, the 6S model is used, as it can more accurately simulate the radiation process required by this invention and is the most reasonable choice for obtaining the most accurate inter-band correction coefficients.

[0023] S3, Based on the correction coefficient, construct a radiance-based ground chlorophyll index by correcting the traditional reflectance ground chlorophyll index.

[0024] S4. Construct a regression model between the correction coefficient and chlorophyll, and select the optimal model. Multiple inversion regression models can be selected for inversion attempts. Common models include linear, quadratic, cubic, logarithmic, exponential, and power models, as shown in Table 2. The most suitable model can be selected based on the relevant inversion results.

[0025] S5, Chlorophyll is inverted based on the correction coefficient and the constructed regression model.

[0026] In one embodiment, in step S2, the 6S radiative transfer model can be used for simulation. The 6S model (Second Simulation of the Satellite Signal in the Solar Spectrum) is a widely used method in radiative transfer models. It is an improvement on the 5S model (Simulation of the Satellite Signal in the Solar Spectrum), incorporating the latest scattering calculation algorithms and establishing a relevant model using the principle of electromagnetic wave radiative transfer in the atmosphere. According to the technical problem to be solved by this invention, the parameters that need to be set during the simulation are shown in Table 1:

[0027] Table 1 6S Model Parameter Settings

[0028]

[0029]

[0030] Depending on different atmospheric conditions or specific requirements, the parameters can be adjusted appropriately within the default range according to the actual situation.

[0031] A specific embodiment of the present invention is described below.

[0032] 1) Calculated using the 6S model:

[0033] direct solar irradiance (s.outputs.direct_solar_irradiance), solar diffuse irradiance (s.outputs.diffuse_solar_irradiance), and ambient irradiance (s.outputs.environmental_irradiance).

[0034] Then, the sum of these three values ​​for each band is calculated to obtain the radiance value, as shown in the following formula:

[0035]

[0036] 2) Calculate the correction factors a and b under various atmospheric conditions, and take the median of each as the final value.

[0037]

[0038]

[0039] Where E represents the incident radiance, corresponding to different wavebands.

[0040] After simulation calculation, the final values ​​of the correction coefficients a and b are: a = 1.1595 and b = 1.0924. These values ​​can remain fixed in future use and do not need to be recalculated.

[0041] 3) Based on the correction coefficient, a radiance-based ground chlorophyll index is constructed by correcting the traditional reflectance ground chlorophyll index.

[0042] The traditional ground chlorophyll index is calculated using the following equation:

[0043]

[0044] In this equation, r represents the reflectivity of different wavelength bands, and its calculation equation is as follows:

[0045]

[0046] Where L represents the radiance reflected by the blades in each band, which can be directly obtained from a spectrometer; E is the incident radiance, corresponding to different bands. Substituting formula (5) into (4) yields:

[0047]

[0048] Now, introducing the correction coefficients a and b from formulas (2) and (3), and substituting them into formula (4), we obtain:

[0049]

[0050] Substituting a = 1.1595 and b = 1.0924, the new radiance-based ground chlorophyll index (RMTCI) can be expressed as:

[0051]

[0052] Then, a regression model between the index and chlorophyll can be constructed, and the optimal model can be selected. Chlorophyll can then be retrieved based on the index and the constructed statistical model.

[0053] The method of this invention is applicable to any ratio-type vegetation index for the inversion of chlorophyll or other crop parameters. The corresponding correction coefficients can be re-simulated and calculated for the bands involved in the vegetation index to be applied.

[0054] The method of this invention was tested, and the experimental results are as follows: The geographical location of the plants and the measurement time were recorded. Using a SEI-RS-8800 spectrometer and a SPAD-502plus chlorophyll meter, under different weather conditions (sunny days, cloudy days, etc.), vertical photography and measurement were performed on the leaves of a total of 45 plants (summer maize) in six rounds. Spectral data such as irradiance and reflectance of the upper and lower leaves, as well as related biomass data such as chlorophyll, were obtained. Simultaneously, the ground chlorophyll index based on irradiance was calculated according to this invention, and chlorophyll inversion was performed. The results are shown in Table 2 below.

[0055] Table 2 Chlorophyll inversion results

[0056]

[0057] Note: Radiance* indicates the result obtained by inverting the ground chlorophyll index after introducing the correction coefficient; the formula for calculating regression accuracy is: Regression Accuracy = RMSE / Sample Chlorophyll Mean.

[0058] The data in Table 2 demonstrates that the present invention exhibits good performance in terms of correlation and accuracy in the final inversion results. Furthermore, the present invention does not overly focus on the selection of the final inversion model. As shown in Table 2, any commonly used inversion model can be applied to the final inversion process of the present invention.

[0059] The embodiments described above are merely preferred embodiments of the present invention. The terms "in one embodiment," "in another embodiment," "in yet another embodiment," or "in still another embodiment" used in this specification all refer to one or more of the same or different embodiments according to this disclosure. Ordinary variations and substitutions made by those skilled in the art within the scope of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for retrieving chlorophyll of plant leaves based on radiance, characterized in that, The method comprises the following steps: S1, measuring the radiance values of plant leaves in different wave bands; S2, according to the proportion of different wave bands of solar irradiance in the incident solar radiation, a correction coefficient for the traditional reflectivity ground leaf chlorophyll index is calculated, and the correction coefficient is obtained through the following process: 1) the direct solar irradiance is calculated the solar scattered irradiance and the ambient irradiance The sum of the three values of each wave band is calculated as the radiance: 2) the ratio of the radiance of different wave bands under different atmospheric conditions is calculated as the correction coefficient: the correction coefficients a and b under different atmospheric conditions are calculated, and the median values are taken as the final values, wherein E is the radiance; S3, constructing a radiance-based ground leaf chlorophyll index based on the correction coefficient by correcting a traditional reflectance-based ground leaf chlorophyll index; S4, constructing a regression model between the correction coefficient and chlorophyll; S5, inverting chlorophyll based on the correction coefficient and the constructed regression model.

2. The method of claim 1, wherein the method is based on radiance. The ground leaf chlorophyll index is a radiance-based ratio vegetation index.

3. The method of claim 1, wherein the method is based on radiance. In step S2, the correction coefficient is simulated by a 6S radiation transfer model.

4. The radiance-based plant leaf chlorophyll inversion method according to claim 1, wherein, In step S1, the different wave bands comprise 750 nm, 710 nm and 680 nm. In step S2, the correction coefficients a and b of 750 nm to 680 nm and 710 nm to 680 nm are simulated.

5. The radiance-based plant leaf chlorophyll inversion method according to claim 1, wherein, In step S3, the ground leaf chlorophyll index is calculated by the following steps: 1) Calculate the traditional ground chlorophyll index: 2) Calculate reflectance r for different wavebands: L represents the radiance reflected by the leaf for each waveband; 3) The ground leaf chlorophyll index is calculated by the following equation: 4) Introducing correction coefficients a, b, calculating the ground chlorophyll index by the following formula:

6. The method of claim 5, wherein the method is based on radiance. The radiance-based ground leaf chlorophyll index is calculated by the following formula:

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