A rice canopy bidirectional reflectivity simulation method and system

Abstract

The present invention discloses a method and system for simulating the bidirectional reflectance of a rice canopy. The method comprises setting canopy vertical structure parameters and canopy component parameters according to the growth stage and growth characteristics of the rice, inputting the two parameters into a SAIL model, constructing a rice canopy radiation transmission model, and then inputting the soil reflectance, leaf area of ​​each vertical layer, leaf reflectance and leaf transmittance of different vertical layers, incident specular radiation ratio, simulated rice leaf inclination distribution function, solar zenith angle, observation zenith angle, and observation azimuth angle of each rice canopy growth stage into the constructed rice canopy radiation transmission model to simulate the canopy reflectance of the rice at each growth stage. Compared with the traditional canopy radiation transmission model, the present invention introduces rice canopy component parameters and quantitatively characterizes the heterogeneous distribution characteristics of the canopy vertical structure, significantly improving the simulation accuracy of the bidirectional reflectance of the canopy at each growth stage of the rice.

Description

Technical Field

[0001] The invention belongs to the technical field of agricultural remote sensing, and in particular relates to a method and system for simulating bidirectional reflectance of a rice canopy. Background Art

[0002] Crop canopy reflectance simulation is a critical bridge between remote sensing observations and vegetation phenotypic parameters, and its accuracy directly determines the reliability of the inversion results. Agricultural remote sensing observations capture radiation information from the upper canopy boundary, after multiple scattering and absorption by the coupled vegetation-soil system. This physical process can be systematically described using radiative transfer theory. This theory not only accurately simulates the radiation field at the upper canopy boundary but, more importantly, establishes a quantitative relationship between the radiation signal and crop biophysical parameters, fundamentally addressing the quantification problem in agricultural remote sensing. For example, the rice canopy has a relatively uniform but complex optical structure (manifested by the random distribution and multi-layered structure of leaves). Through canopy radiative transfer modeling, we can accurately analyze the three-dimensional distribution of incident radiation within the canopy and quantitatively describe the scattering, absorption, and transmission processes of photosynthetic and canopy components (leaves, stems, soil, etc.). This provides a scientific basis for constructing a physical relationship model between the "radiative signal" and crop characteristics and addressing "ill-posed" problems in remote sensing inversion.

[0003] The SAIL (Scattering by Arbitrary Inclined Leaves) model, developed by Verhoef and Bunnik and extending the Suits model, is one of the earliest and most widely used crop canopy radiative transfer models. The SAIL model simulates the interaction between incident radiation and the uniform medium by assuming the canopy is composed of horizontal, uniform, and infinitely extending isotropic leaves with a given geometry and density. It solves for the intensities of upward and downward scattered light within the canopy to simulate canopy reflectance close to reality in the 400nm-2500nm range. By mathematically representing the directional reflectance characteristics of the vegetation canopy under different combinations of solar incidence angles and sensor observation angles, the model accurately characterizes the three-dimensional structural properties of vegetation and its interaction with electromagnetic waves. It plays an irreplaceable role in vegetation parameter inversion, angular normalization of multi-source remote sensing data, and surface energy balance estimation. It is particularly valuable for precision agricultural management (such as crop growth monitoring) and global change research (such as carbon cycle simulation).

[0004] Current mainstream canopy radiative transfer models still have significant limitations when simulating the reflectance properties of crops such as rice. These limitations are primarily manifested in the following two aspects: First, they inadequately represent the dynamic growth process. Existing models generally use static parameters to describe canopy structure, failing to fully account for the temporal variations in key components during the rice growth period (such as water disturbance during the tillering period, panicle proportion during heading, and yellow leaf proportion during maturity). Second, they lack representation of vertical heterogeneity. Traditional models often assume a homogeneous canopy, but the actual rice canopy exhibits significant vertical stratification (e.g., differences in optical properties between upright leaves in the upper canopy and senescent leaves in the lower canopy). This simplification leads to biased estimates of multiple scattering effects, particularly at high zenith angles. These limitations pose significant challenges to existing models in simulating the bidirectional reflectance properties of heterogeneous crop canopies such as rice, hindering the accuracy of remote sensing retrievals. There is an urgent need to develop novel canopy reflectance simulation methods that integrate rice growth characteristics with canopy radiative transfer mechanisms to accurately represent the dynamic optical properties of the rice canopy. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the present invention provides a method for simulating bidirectional reflectance of a rice canopy, comprising the following steps:

[0006] Step 1: Obtain the canopy reflectance, soil reflectance, leaf inclination angle, and whiteboard and blackboard reflectance during instrument measurement at each growth stage of rice. Measure the leaf area of ​​each vertical layer at each growth stage of rice. Collect the leaf reflectance of leaves in different vertical layers at each growth stage of rice with whiteboard and blackboard as backgrounds. Record the location of the observation point, the location of the target rice plant, the observation date, the height of the observation equipment, the observation direction, and the proportion of incident specular radiation.

[0007] Step 2: Calculate the leaf reflectivity and leaf transmittance of different vertical layers at each growth stage of rice, calculate the leaf inclination angle distribution probability of rice, and establish a simulated rice leaf inclination angle distribution function;

[0008] Step 3: Calculate the solar zenith angle using the position of the observation point and the observation date, calculate the observation zenith angle using the position of the target rice plant, the height of the observation equipment, and the observation direction, and calculate the observation azimuth using the position of the observation point and the position of the target rice plant;

[0009] Step 4: Set the canopy vertical structure parameters and canopy component parameters according to the growth stage and growth characteristics of the rice, input the two parameters into the SAIL model, and construct the rice canopy radiation transfer model;

[0010] Step 5: Use the constructed rice canopy radiation transfer model to simulate the canopy reflectivity at each growth stage of rice.

[0011] Furthermore, in step 1, the reflectance of the rice canopy, the reflectance of the soil, and the reflectance of the leaves of different vertical layers of rice with a white board and a black board as the background are collected using a ground object hyperspectral instrument at the tillering stage, jointing stage, booting stage, heading stage, filling stage and maturity stage of the rice, and the reflectance of the white board and the reflectance of the black board during the measurement by the ground object hyperspectral instrument are recorded; the leaf inclination angle is measured using a protractor at the tillering stage, jointing stage, booting stage, heading stage, filling stage and maturity stage of the rice, and the leaf area of ​​each layer of the rice in different vertical layers is measured using a leaf area meter.

[0012] Furthermore, the calculation formulas for the leaf reflectivity and leaf transmittance of different vertical layers at different growth stages of rice in step 2 are as follows:

[0013] (1)

[0014] (2)

[0015] Where, is the leaf reflectivity, is the leaf transmittance, and They represent the whiteboard reflectivity and blackboard reflectivity when measured by the instrument, and Respectively represent the reflectance of rice leaves measured using blackboard and whiteboard as background;

[0016] The leaf transmittance and leaf reflectance can be obtained by jointly solving equations (1) and (2):

[0017] (3)

[0018] (4)

[0019] Substitute the leaf inclination angle and leaf inclination angle distribution probability of rice into the adaptive Sigmoid function to establish a simulated rice leaf inclination angle distribution function. The specific calculation formula is:

[0020] (5)

[0021] Where, a To determine the peak value of the curve, b To determine the steepness of the curve, c is a velocity coefficient, e is the base of the natural logarithm function, x is the leaf inclination angle, in degrees, y is the distribution probability of the leaf inclination angle.

[0022] Furthermore, the solar zenith angle in step 3 is calculated using the Meinel formula, and the specific calculation formula is as follows:

[0023] (6)

[0024] (7)

[0025] (8)

[0026] Where, tts is the solar zenith angle; is the latitude of the observation point, with north latitude being positive and south latitude being negative; is the latitude of the sun's direct point, which is approximately calculated based on the observation date; N is the date number in a year; h is the solar hour angle, with each 15° representing 1 hour, negative in the morning and positive in the afternoon. The calculation is as follows:

[0027] (9)

[0028] Where, Indicates local solar time.

[0029] The observation zenith angle is calculated using the observation geometry modeling method. The specific calculation formula is as follows:

[0030] (11)

[0031] Where, tto is the observation zenith angle; R is the radius of the earth; H is the height of the observation equipment; is the central angle between the observation point and the target rice, that is, the observation direction, which is calculated using the Haversine formula. The specific formula is as follows:

[0032] (12)

[0033] (13)

[0034] (14)

[0035] (15)

[0036] Where, is an intermediate variable, 、 are the latitudes of the target rice and observation points, 、 are the longitudes of the target rice and observation points, is the latitude difference between the target rice plant and the observation point, is the longitude difference between the target rice plant and the observation point.

[0037] The observation azimuth is calculated using spherical trigonometry. The specific calculation formula is as follows:

[0038] (17)

[0039] (18)

[0040] Where, psi is the observation azimuth, is the four-quadrant inverse tangent function, 、 are the latitudes of the target rice and observation points, 、 are the longitudes of the target rice and observation points, is the latitude difference between the target rice plant and the observation point.

[0041] Furthermore, in step 4, at each growth stage of rice, the rice canopy is divided into different vertical layers from top to bottom, and the canopy vertical structure parameters and canopy component parameters are set according to the growth stage and growth characteristics of the rice. Specifically: in the tillering stage of rice, the vertical direction is 1 layer, and the canopy components only have light green leaves; in the jointing stage of rice, the vertical direction is 1 layer, and the canopy components are light green leaves and dark green leaves; in the booting stage of rice, the vertical direction is 2 layers, and the canopy components are dark green leaves and sword leaves; in the heading stage of rice, the vertical direction is 2 layers, and the canopy components are dark green leaves, sword leaves and green ears; in the filling stage of rice, the vertical direction is 3 layers, and the canopy components are dark green leaves, yellow-green ears and yellow-green leaves; in the maturity stage of rice, the vertical direction is 3 layers, and the canopy components are yellow-green leaves, yellow ears and yellow leaves.

[0042] The vertical structure parameters and canopy component parameters of rice at different growth stages are input into the SAIL model to construct the rice canopy radiation transfer model, namely:

[0043] (20)

[0044] Where, is the canopy reflectance, is the rice canopy radiation transfer model, For rice i The reflectivity of the leaves of the species, For rice i The leaf transmittance of the leaf, For rice i The leaves are in the vertical direction j Leaf area of ​​the layer, When the corresponding green leaves, When the corresponding dark green leaves, When, corresponding to the sword leaf, When, it corresponds to the green spike, When the yellow-green spike is When the corresponding yellow-green leaves, When, it corresponds to the yellow spike, When the corresponding yellow leaves, To simulate the rice leaf inclination angle distribution function, is the incident specular radiation ratio, tts is the solar zenith angle, tto To observe the zenith angle, psi is the observation azimuth, is the soil reflectivity.

[0045] Furthermore, in step 5, the soil reflectivity at each growth stage of rice, the leaf area of ​​each layer in the vertical layer and the proportion of incident specular radiation at each growth stage of rice obtained in step 1, the leaf reflectivity of different vertical layers in each growth stage of rice obtained in step 2, the leaf transmittance of different vertical layers in each growth stage of rice and the simulated rice leaf inclination distribution function, and the solar zenith angle, observation zenith angle and observation azimuth calculated in step 3 are input into the rice canopy radiation transmission model constructed in step 4 to achieve simulation of the canopy reflectivity at each growth stage of rice.

[0046] The present invention also provides a rice canopy bidirectional reflectance simulation system for realizing the rice canopy bidirectional reflectance simulation method as described above.

[0047] Furthermore, the invention comprises a processor and a memory, wherein the memory is used to store program instructions, and the processor is used to call the stored instructions in the memory to execute the above-mentioned rice canopy bidirectional reflectance simulation method.

[0048] Compared with the prior art, the present invention has the following advantages:

[0049] 1) Compared with traditional canopy radiation transfer models, the rice canopy radiation transfer model established in this paper introduces rice canopy component parameters and quantitatively characterizes the heterogeneous distribution characteristics of the canopy vertical structure. It is more suitable for simulating the radiation transfer process of rice at various growth stages, significantly improving the simulation accuracy of the bidirectional reflectance of the rice canopy at various growth stages, and realizing effective simulation of the bidirectional reflectance of the rice canopy;

[0050] 2) Verified by ground-based measured data, the proposed method achieved high-precision simulation results and can be applied to analyze the influence of canopy component parameters and vertical structural characteristics on canopy reflectance. It is of great significance in the inversion of various phenotypic values ​​such as rice chlorophyll content, leaf area index, and biomass, as well as in field precision crop management. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0052] Figure 1 This is a flow chart of a method for simulating bidirectional reflectance of a rice canopy according to an embodiment of the present invention.

[0053] Figure 2 The reflectivity of rice leaves was measured in the field using a white board and a black board as backgrounds, respectively, according to an embodiment of the present invention.

[0054] Figure 3 The blade reflectivity and blade transmittance calculated in the embodiment of the present invention.

[0055] Figure 4 It is a comparison diagram of the blade inclination angle function measured in an embodiment of the present invention, the vertical blade inclination angle function, and the blade inclination angle function simulated by the present invention.

[0056] Figure 5 This is a comparison chart of the measured canopy reflectance, SAIL simulated canopy reflectance, and Rice-SAIL simulated canopy reflectance according to an embodiment of the present invention. DETAILED DESCRIPTION

[0057] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention are further described below with reference to the accompanying drawings and embodiments. It is obvious that the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0058] Example 1

[0059] Taking 27 rice varieties planted in a rice base as an example, the specific implementation process of the rice canopy bidirectional reflectance simulation method of the present invention is described. The 27 rice varieties include 9 varieties of red lotus type, wild abortive type indica rice and japonica rice. The rice was sown on May 15, 2022, transplanted on June 15, 2022, and harvested on September 28, 2022. The area of ​​each planting area is , the planting density is .

[0060] like Figure 1 As shown, the embodiment of the present invention provides a method for simulating bidirectional reflectance of a rice canopy, comprising the following steps:

[0061] Step 1: Obtain the canopy reflectance, soil reflectance, leaf inclination angle, whiteboard reflectance and blackboard reflectance during instrument measurement at each growth stage of rice, measure the leaf area of ​​each vertical layer of rice at each growth stage, collect the leaf reflectance of leaves in different vertical layers of rice at each growth stage with whiteboard and blackboard as background, and record the location of the observation point, the location of the target rice, the observation date, the height of the observation equipment, the observation direction and the proportion of incident specular radiation.

[0062] A hyperspectral instrument was used to collect rice canopy reflectance, soil reflectance, and leaf reflectance at different vertical layers against white and black backgrounds during the tillering, jointing, booting, heading, grain filling, and maturity stages of rice. The white and black background reflectances were recorded during the measurements. The hyperspectral instrument was mounted on a ground platform. Active mode was used to measure leaf reflectance at different vertical layers of rice at each growth stage against white and black backgrounds, carefully avoiding leaf veins. Passive mode was used to measure canopy and soil reflectance at each growth stage. The optical fiber of the hyperspectral instrument was perpendicular to the canopy (or soil) and held 1 meter above the canopy. Leaf inclination angle was measured using a protractor, and leaf area per layer was measured using a leaf area meter at different vertical layers during the tillering, jointing, booting, heading, grain filling, and maturity stages of rice.

[0063] Step 2: Calculate the leaf reflectivity and leaf transmittance of different vertical layers of rice at each growth stage using the leaf reflectivity of the leaves at different vertical layers of rice at each growth stage obtained in step 1 with a white board and a black board as backgrounds, and the white board reflectivity and the black board reflectivity during instrument measurement at each growth stage of rice. Statistically calculate the leaf inclination angle distribution probability of rice using the leaf inclination angle of rice at each growth stage obtained in step 1, and establish a simulated rice leaf inclination angle distribution function.

[0064] The calculation formulas for leaf reflectivity and leaf transmittance in different vertical layers at different growth stages of rice are:

[0065] (1)

[0066] (2)

[0067] Where, is the leaf reflectivity, is the leaf transmittance, and They represent the whiteboard reflectivity and blackboard reflectivity when measured by the instrument, and Respectively represent the reflectance of rice leaves measured using a blackboard and a white board as the background.

[0068] The leaf transmittance can be obtained by solving equations (1) and (2) together: for:

[0069] (3)

[0070] Substituting Equation (3) into Equation (1) or Equation (2), we can get the leaf reflectivity for:

[0071] (4)

[0072] Figure 2 The reflectance of rice leaves measured in the field using a white board and a black board as the background, Figure 3 are the calculated leaf reflectivity and leaf transmittance.

[0073] Substitute the leaf inclination angle and leaf inclination angle distribution probability of rice into the adaptive Sigmoid function to establish a simulated rice leaf inclination angle distribution function. The specific calculation formula is:

[0074] (5)

[0075] Where, a To determine the peak value of the curve, b To determine the steepness of the curve, c is a velocity coefficient, e is the base of the natural logarithm function, x is the leaf inclination angle, in degrees, y is the distribution probability of the leaf inclination angle.

[0076] This embodiment calculates: a =2.705, b =5.942, c =0.09332. Figure 4 The comparison diagram of the measured leaf inclination angle distribution function, the vertical leaf inclination angle distribution function and the simulated leaf inclination angle distribution function established by the present invention is shown in Figure 2. The correlation analysis of the leaf inclination angle distribution function simulated by the present invention and the leaf inclination angle values ​​measured at each growth stage of rice is performed to obtain R 2 =0.9621, RMSE=0.02361.

[0077] Step 3: Calculate the solar zenith angle using the position of the observation point and the observation date recorded in step 1, calculate the observation zenith angle using the position of the target rice plant, the height of the observation equipment, and the observation direction recorded in step 1, and calculate the observation azimuth using the position of the observation point and the position of the target rice plant recorded in step 1.

[0078] Calculate the solar zenith angle using the Meinel formula tts , the specific calculation formula is as follows:

[0079] (6)

[0080] (7)

[0081] (8)

[0082] Where, is the latitude of the observation point, with north latitude being positive and south latitude being negative; is the latitude of the sun's direct point, which is approximately calculated based on the observation date; N is the date number in a year; h is the solar hour angle, with each 15° representing 1 hour, negative in the morning and positive in the afternoon. The calculation is as follows:

[0083] (9)

[0084] Where, Indicates local solar time.

[0085] At noon, , formula (6) can be simplified to:

[0086] (10)

[0087] Calculating the Observation Zenith Angle Using Observational Geometry Modeling tto , the specific calculation formula is as follows:

[0088] (11)

[0089] Where R is the radius of the Earth, which is approximately 6371 km; H is the height of the observation equipment; is the central angle between the observation point and the target rice, that is, the observation direction, which is calculated using the Haversine formula. The specific formula is as follows:

[0090] (12)

[0091] (13)

[0092] (14)

[0093] (15)

[0094] Where, is an intermediate variable, 、 are the latitudes of the target rice and observation points, 、 are the longitudes of the target rice and observation points, is the latitude difference between the target rice plant and the observation point, is the longitude difference between the target rice plant and the observation point.

[0095] When the observation device is on the ground, H=0, and the target point is near the ground, then:

[0096] (16)

[0097] Calculate observation azimuth using spherical trigonometry psi , the specific calculation formula is as follows:

[0098] (17)

[0099] (18)

[0100] Where, is the four-quadrant inverse tangent function, 、 They are 、 are the latitudes of the target rice and observation points, 、 are the longitudes of the target rice and observation points, is the latitude difference between the target rice plant and the observation point.

[0101] Step 4: At each growth stage of rice, the rice canopy is divided into different vertical layers from top to bottom. The canopy vertical structure parameters and canopy component parameters are set according to the growth stage and growth characteristics of the rice. The rice canopy vertical structure parameters and canopy component parameters are input into the SAIL model to construct a rice canopy radiation transfer model.

[0102] The canopy vertical structure parameters and canopy component parameters were set according to the growth stage and growth characteristics of rice, as shown in Table 1.

[0103] Table 1 Canopy vertical structure parameters and canopy component parameters at different growth stages

[0104]

[0105] As shown in Table 1, during the tillering stage of rice, there is one layer in the vertical direction, and the canopy components are only light green leaves; during the jointing stage of rice, there is one layer in the vertical direction, and the canopy components are light green leaves and dark green leaves; during the booting stage of rice, there are two layers in the vertical direction, and the canopy components are dark green leaves and sword leaves; during the heading stage of rice, there are two layers in the vertical direction, and the canopy components are dark green leaves, sword leaves, and green ears; during the filling stage of rice, there are three layers in the vertical direction, and the canopy components are dark green leaves, yellow-green ears, and yellow-green leaves; during the maturity stage of rice, there are three layers in the vertical direction, and the canopy components are yellow-green leaves, yellow ears, and yellow leaves.

[0106] The formula for simulating the bidirectional reflectance of rice canopy by SAIL model is as follows:

[0107] (19)

[0108] Where, is the canopy reflectance; is a scattering canopy radiation transfer model for arbitrarily tilted leaves; and are leaf reflectance and leaf transmittance, respectively. The SAIL model assumes that rice leaves are identical at all growth stages, so the leaf reflectance / leaf transmittance of each leaf is also the same; LAD is the vertical rice leaf inclination distribution function; LAI is the leaf area of ​​the entire plant, that is, the sum of the leaf areas of each layer; is the incident specular radiation ratio, and when the target point is a rough vegetation canopy, the value range is between 0 and 0.1; tts is the solar zenith angle; tto is the observation zenith angle; psi is the observation azimuth; is the soil reflectivity.

[0109] The canopy vertical structure parameters and canopy component parameters of rice at each growth stage set by the present invention are input into the SAIL model to construct a rice canopy radiation transfer model (Rice-SAIL). The specific calculation formula is as follows:

[0110] (20)

[0111] Where, is the canopy reflectance, is the rice canopy radiation transfer model, For rice i The reflectivity of the leaves of the species, For rice i The leaf transmittance of the leaf, For rice i The leaves are in the vertical direction j Leaf area of ​​the layer, When the corresponding green leaves, When the corresponding dark green leaves, When, corresponding to the sword leaf, When, it corresponds to the green spike, When the yellow-green spike is When the corresponding yellow-green leaves, When, it corresponds to the yellow spike, When the corresponding yellow leaves, To simulate the rice leaf inclination angle distribution function, is the incident specular radiation ratio, tts is the solar zenith angle, tto To observe the zenith angle, psi is the observation azimuth, is the soil reflectivity.

[0112] When rice is in the tillering stage, i The value is 1. j The value is 1. is the reflectance of the tender green leaves of rice, is the leaf transmittance of the tender green rice leaves, It refers to the leaf area of ​​the first layer of light green leaves in the vertical direction.

[0113] When rice is in the jointing stage, i The values ​​are 1 and 2. j The value is 1. is the reflectance of the tender green leaves of rice, is the reflectance of dark green rice leaves, is the leaf transmittance of the tender green rice leaves, is the leaf transmittance of dark green rice leaves, It is the leaf area of ​​the first layer of tender green leaves in the vertical direction. It refers to the leaf area of ​​the first layer of dark green leaves in the vertical direction.

[0114] When rice is in the heading stage, i The values ​​are 2 and 3. j The values ​​are 1 and 2. is the reflectance of dark green rice leaves, is the reflectance of the rice flag leaf, is the leaf transmittance of dark green rice leaves, is the leaf transmittance of rice flag leaf, It is the leaf area of ​​the first layer of dark green leaves in the vertical direction. It is the leaf area of ​​the second layer of dark green leaves in the vertical direction. is the leaf area of ​​the first layer of the sword leaf in the vertical direction, It is the leaf area of ​​the second layer of the flag leaf in the vertical direction.

[0115] When rice is in the heading stage, i The values ​​are 2, 3 and 4. j The values ​​are 1 and 2. is the reflectance of dark green rice leaves, is the reflectance of the rice flag leaf, is the leaf reflectance of the green ear of rice, is the leaf transmittance of dark green rice leaves, is the leaf transmittance of rice flag leaf, is the leaf transmittance of the green panicle of rice, is the leaf area of ​​the first layer in the vertical direction of the dark green leaves, It is the leaf area of ​​the second layer of dark green leaves in the vertical direction. is the leaf area of ​​the first layer of the sword leaf in the vertical direction, is the leaf area of ​​the second layer of the sword leaf in the vertical direction, is the leaf area of ​​the first layer of green spike leaves in the vertical direction, It is the leaf area of ​​the second layer of green spike leaves in the vertical direction.

[0116] When rice is in the grain filling stage, i The values ​​are 2, 5 and 6. j The values ​​are 1, 2 and 3. is the reflectance of dark green rice leaves, is the reflectance of the yellow-green rice ear leaves, is the reflectance of the yellow-green leaves of rice, is the leaf transmittance of dark green rice leaves, is the leaf transmittance of the yellow-green rice panicle, is the leaf transmittance of the yellow-green rice leaf, It is the leaf area of ​​the first layer of dark green leaves in the vertical direction. It is the leaf area of ​​the second layer of dark green leaves in the vertical direction. It is the leaf area of ​​the third layer of dark green leaves in the vertical direction. It is the leaf area of ​​the first layer of yellow-green spike in the vertical direction, The leaf area of ​​the second layer of the yellow-green spike in the vertical direction, The leaf area of ​​the third layer of yellow-green spike in the vertical direction, It is the leaf area of ​​the first layer of yellow-green leaves in the vertical direction. is the leaf area of ​​the second layer of yellow-green leaves in the vertical direction, It is the leaf area of ​​the third layer of yellow-green leaves in the vertical direction.

[0117] When rice is mature, i The values ​​are 6, 7 and 8. j The values ​​are 1, 2 and 3. is the reflectance of the yellow-green leaves of rice, is the leaf reflectance of yellow rice spike, is the reflectance of yellow rice leaves, is the leaf transmittance of the yellow-green rice leaf, is the leaf transmittance of yellow rice panicle, is the leaf transmittance of yellow rice leaves, It is the leaf area of ​​the first layer of yellow-green leaves in the vertical direction. is the leaf area of ​​the second layer of yellow-green leaves in the vertical direction, It is the leaf area of ​​the third layer of yellow-green leaves in the vertical direction. is the leaf area of ​​the first layer of yellow spike in the vertical direction, is the leaf area of ​​the second layer of yellow spike in the vertical direction, is the leaf area of ​​the third layer of yellow spike in the vertical direction, is the leaf area of ​​the first layer of yellow leaves in the vertical direction, is the leaf area of ​​the second layer of yellow leaves in the vertical direction, It is the leaf area of ​​the third layer of yellow leaves in the vertical direction.

[0118] Step 5: Input the soil reflectivity at each growth stage of rice obtained in step 1, the leaf area of ​​each layer in the vertical layer and the proportion of incident specular radiation at each growth stage of rice, the leaf reflectivity of different vertical layers in each growth stage of rice obtained in step 2, the leaf transmittance of different vertical layers in each growth stage of rice and the simulated rice leaf inclination distribution function, and the solar zenith angle, observation zenith angle and observation azimuth calculated in step 3 into the rice canopy radiation transmission model constructed in step 4 to simulate the canopy reflectivity at each growth stage of rice.

[0119] The simulation effect was evaluated by comparing the bidirectional reflectance of the rice canopy at each growth stage simulated by the method proposed in the present invention with the measured value and the SAIL simulation value. Figure 5 The results show the comparison of the measured bidirectional reflectance of rice canopy, the bidirectional reflectance of rice canopy simulated by SAIL model and the bidirectional reflectance of rice canopy simulated by Rice-SAIL model of the present invention. Figure 5 It can be seen that the Rice-SAIL simulation proposed in the present invention is closest to the measured value, which significantly improves the accuracy of the bidirectional reflectance of the rice canopy.

[0120] Example 2

[0121] Based on the same inventive concept, the present invention also provides a rice canopy bidirectional reflectance simulation system, including a processor and a memory, the memory is used to store program instructions, and the processor is used to call the program instructions in the memory to execute the above-mentioned rice canopy bidirectional reflectance simulation method.

[0122] In specific implementation, the method proposed in the technical solution of the present invention can be automatically run by those skilled in the art using computer software technology. System devices that implement the method, such as computer-readable storage media that store the corresponding computer program of the technical solution of the present invention and computer equipment that runs the corresponding computer program, should also be within the scope of protection of the present invention.

[0123] The specific embodiments described herein are merely illustrative of the spirit of the present invention. Persons skilled in the art may make various modifications, additions, or substitutions to the described specific embodiments without departing from the spirit of the present invention or exceeding the scope of the appended claims.

Claims

1. A method for simulating bidirectional reflectance of a rice canopy, characterized in that: The following steps are involved: Step 1: Obtain the canopy reflectance, soil reflectance, leaf inclination angle, and whiteboard and blackboard reflectance during instrument measurement at each growth stage of rice. Measure the leaf area of ​​each vertical layer at each growth stage of rice. Collect the leaf reflectance of leaves in different vertical layers at each growth stage of rice with whiteboard and blackboard as backgrounds. Record the location of the observation point, the location of the target rice plant, the observation date, the height of the observation equipment, the observation direction, and the proportion of incident specular radiation. Step 2: Calculate the leaf reflectivity and leaf transmittance of different vertical layers at each growth stage of rice, calculate the leaf inclination angle distribution probability of rice, and establish a simulated rice leaf inclination angle distribution function; The calculation formulas for leaf reflectivity and leaf transmittance in different vertical layers at different growth stages of rice are: （1） （2） Where, is the leaf reflectivity, is the leaf transmittance, and They represent the whiteboard reflectivity and blackboard reflectivity when measured by the instrument, and Respectively represent the reflectance of rice leaves measured using blackboard and whiteboard as background; The leaf transmittance and leaf reflectance can be obtained by jointly solving equations (1) and (2): （3） （4） Substitute the leaf inclination angle and leaf inclination angle distribution probability of rice into the adaptive Sigmoid function to establish a simulated rice leaf inclination angle distribution function. The specific calculation formula is: （5） Where, a To determine the peak value of the curve, b To determine the steepness of the curve, c is a velocity coefficient, e is the base of the natural logarithm function, x is the leaf inclination angle, in degrees, y is the distribution probability of the leaf inclination angle; Step 3: Calculate the solar zenith angle using the position of the observation point and the observation date, calculate the observation zenith angle using the position of the target rice plant, the height of the observation equipment, and the observation direction, and calculate the observation azimuth using the position of the observation point and the position of the target rice plant; Step 4: Set the canopy vertical structure parameters and canopy component parameters according to the growth stage and growth characteristics of the rice, input the two parameters into the SAIL model, and construct the rice canopy radiation transfer model; Step 5: Use the constructed rice canopy radiation transfer model to simulate the canopy reflectivity at each growth stage of rice.

2. The method for simulating bidirectional reflectance of a rice canopy according to claim 1, wherein: In step 1, the reflectance of the rice canopy, the reflectance of the soil, and the reflectance of the leaves of rice in different vertical layers with a white board and a black board as the background are collected using a ground object hyperspectral instrument at the tillering stage, jointing stage, booting stage, heading stage, filling stage and maturity stage of rice, and the reflectance of the white board and the reflectance of the black board are recorded during the measurement by the ground object hyperspectral instrument; the leaf inclination angle is measured using a protractor at the tillering stage, jointing stage, booting stage, heading stage, filling stage and maturity stage of rice, and the leaf area of ​​each layer of rice in different vertical layers is measured using a leaf area meter.

3. The method for simulating bidirectional reflectance of a rice canopy according to claim 1, wherein: In step 3, the solar zenith angle is calculated using the Meinel formula. The specific calculation formula is as follows: （6） （7） （8） Where, tts is the solar zenith angle; is the latitude of the observation point, with north latitude being positive and south latitude being negative; is the latitude of the sun's direct point, which is approximately calculated based on the observation date; N is the date number in a year; h is the solar hour angle, with each 15° representing 1 hour, negative in the morning and positive in the afternoon. The calculation is as follows: （9） Where, Indicates local solar time.

4. The method for simulating bidirectional reflectance of a rice canopy according to claim 3, wherein: The observation zenith angle in step 3 is calculated using the observation geometry modeling method. The specific calculation formula is as follows: （11） Where, tto is the observation zenith angle; R is the radius of the earth; H is the height of the observation equipment; is the central angle between the observation point and the target rice, that is, the observation direction, which is calculated using the Haversine formula. The specific formula is as follows: （12） （13） （14） （15） Where, is an intermediate variable, 、 are the latitudes of the target rice and observation points, 、 are the longitudes of the target rice and observation points, is the latitude difference between the target rice plant and the observation point, is the longitude difference between the target rice plant and the observation point.

5. The method for simulating bidirectional reflectance of a rice canopy according to claim 3, wherein: The observation azimuth in step 3 is calculated using spherical trigonometry. The specific calculation formula is as follows: （17） （18） Where, psi is the observation azimuth, is the four-quadrant inverse tangent function, 、 are the latitudes of the target rice and observation points, 、 are the longitudes of the target rice and observation points, is the latitude difference between the target rice plant and the observation point.

6. The method for simulating bidirectional reflectance of a rice canopy according to claim 1, wherein: In step 4, at each growth stage of the rice, the rice canopy is divided into different vertical layers from top to bottom, and the canopy vertical structure parameters and canopy component parameters are set according to the growth stage and growth characteristics of the rice. Specifically: at the tillering stage of the rice, the vertical direction is one layer, and the canopy component only has light green leaves; at the jointing stage of the rice, the vertical direction is one layer, and the canopy components include light green leaves and dark green leaves; During the rice booting stage, there are two layers in the vertical direction, and the canopy components are dark green leaves and flag leaves; during the rice heading stage, there are two layers in the vertical direction, and the canopy components are dark green leaves, flag leaves and green ears; during the rice filling stage, there are three layers in the vertical direction, and the canopy components are dark green leaves, yellow-green ears and yellow-green leaves; during the rice maturity stage, there are three layers in the vertical direction, and the canopy components are yellow-green leaves, yellow ears and yellow leaves.

7. A rice canopy bidirectional reflectance simulation method according to claim 6, characterized in that: In step 4, the vertical structure parameters and canopy component parameters of rice at each growth stage are input into the SAIL model to construct the rice canopy radiation transfer model, namely: （20） Where, is the canopy reflectance, is the rice canopy radiation transfer model, For rice i The reflectivity of the leaves of the species, For rice i The leaf transmittance of the leaf, For rice i The leaves are in the vertical direction j Leaf area of ​​the layer, When the corresponding green leaves, When the corresponding dark green leaves, When, corresponding to the sword leaf, When, it corresponds to the green spike, When the yellow-green spike is When the corresponding yellow-green leaves, When, it corresponds to the yellow spike, When the corresponding yellow leaves, To simulate the rice leaf inclination angle distribution function, is the incident specular radiation ratio, tts is the solar zenith angle, tto To observe the zenith angle, psi is the observation azimuth, is the soil reflectivity.

8. The method for simulating bidirectional reflectance of a rice canopy according to claim 1, wherein: In step 5, the soil reflectivity at each growth stage of rice obtained in step 1, the leaf area of ​​each layer in the vertical layer and the proportion of incident specular radiation at each growth stage of rice, the leaf reflectivity of different vertical layers in each growth stage of rice obtained in step 2, the leaf transmittance of different vertical layers in each growth stage of rice and the simulated rice leaf inclination distribution function, and the solar zenith angle, observation zenith angle and observation azimuth calculated in step 3 are input into the rice canopy radiation transmission model constructed in step 4 to simulate the canopy reflectivity at each growth stage of rice.

9. A rice canopy bidirectional reflectance simulation system, characterized in that: The method comprises a processor and a memory, wherein the memory is used to store program instructions, and the processor is used to call the program instructions in the memory to execute the rice canopy bidirectional reflectance simulation method according to any one of claims 1 to 8.

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