CN-121997529-A - Method and system for simulating rice field radar backscattering coefficient in ear period

CN121997529ACN 121997529 ACN121997529 ACN 121997529ACN-121997529-A

Abstract

The invention relates to the technical field of agricultural remote sensing and information, and particularly discloses a method and a system for simulating a rice field radar backscattering coefficient in a spike period, wherein the method comprises the steps of obtaining geometric and physiological parameters of a rice field and synchronously measuring radar data; dividing a canopy into a spike and leaf mixed layer, a stem and leaf mixed layer and an underlying layer, decomposing five scattering mechanisms of spike, leaf and stem, calculating complex dielectric constants of components based on a model, constructing a fine three-dimensional geometric model of spike, leaf and stem, obtaining scattering matrixes of the components through electromagnetic simulation, calculating interlayer attenuation coefficients and propagation constants by using a forward scattering matrix, calculating phase offsets under different scattering paths, and finally coherently superposing backscattering contributions of the components by combining the phase offsets to obtain a total backscattering electric field and coefficients. According to the invention, by combining the component-level fine electromagnetic simulation with the scene-level radiation transmission theory, the high-precision and high-efficiency scattering simulation is realized, and the remote sensing monitoring of rice is effectively supported.

Inventors

LIU XIANGCHEN
LUO SHANJUN
Fang Zhice
ZHANG WEI
GUO YIXIN
LIANG NAN
ZHAO SHAOSHUAI

Assignees

河南省科学院空天信息研究所

Dates

Publication Date: 20260508
Application Date: 20251209

Claims (10)

1. The method for simulating the radar backscattering coefficient of the paddy field in the ear period is characterized by comprising the following steps of: S1, acquiring and processing data, namely acquiring geometric structural parameters, physiological characteristic parameters and radar backscattering coefficients which are synchronously measured of a paddy field with a spike period to be simulated; S2, layering a rice field canopy, namely dividing the rice field canopy into a spike and leaf mixed layer L1, a stem and leaf mixed layer L2 and a lower cushion surface layer L3 from top to bottom; S3, decomposing scattering mechanisms, namely decomposing according to first-order solution of a radiation transmission equation to obtain five scattering mechanisms respectively corresponding to ear, leaf and stem components, wherein the five scattering mechanisms comprise direct back scattering, underlying surface reflection-scattering body double-station scattering, scattering body double-station scattering-underlying surface reflection, underlying surface reflection-scattering body back scattering-underlying surface reflection and forward scattering, the forward scattering mechanism is used for representing electromagnetic wave propagation attenuation, and the rest scattering mechanisms are used for representing back scattering contribution; S4, simulating dielectric properties of the rice component, namely calculating complex dielectric constants of ears, leaves and stems under different frequencies by using an empirical model of dielectric constants and water content based on the acquired water content parameters of the rice component; s5, three-dimensional geometric modeling of the rice component, namely respectively establishing fine three-dimensional geometric models of rice ears, leaves and stems by using the acquired geometric structural parameters; S6, simulating electromagnetic scattering characteristics of the rice components, namely calculating scattering matrixes of the components corresponding to the five scattering mechanisms under different radar system parameters through electromagnetic simulation software based on the three-dimensional geometric model and the complex dielectric constant; s7, simulating electromagnetic wave attenuation characteristics, namely obtaining attenuation coefficients of electromagnetic waves when the electromagnetic waves propagate in the L1 layer and the L2 layer based on the forward scattering matrix in a statistical average mode, and further calculating to obtain a propagation constant; S8, simulating the spatial positions of the rice components, namely simulating and determining the spatial positions of all the spike, leaf and stem components in the rice field under a global coordinate system according to the scene parameters of the rice field; s9, calculating phase offset of different components in the canopy under each scattering path according to the propagation path of each scattering mechanism, the spatial positions of the components and the attenuation coefficient obtained in the step S7; S10, synthesizing a scattering mechanism, namely taking the phase offset into consideration, performing coherent superposition on different components and scattering electric fields corresponding to the scattering mechanism for representing the backscattering contribution, and synthesizing a total radar backscattering electric field of the paddy field; and S11, calculating a backscattering coefficient, namely calculating a simulated radar backscattering coefficient according to the total radar backscattering electric field.
2. The method according to claim 1, wherein in step S2, the spike-leaf mixture layer L1 comprises spikes and leaves, the L1 layer has a height d 1 , the stem-leaf mixture layer L2 comprises stems and leaves, the L2 layer has a height d 2 , and is located below the L1 layer, and the underlying layer L3 is a water layer or a soil layer, and is located below the L2 layer.
3. The method for simulating the radar back scattering coefficient of paddy field in the ear period according to claim 1, wherein in the step S4, the empirical model of the dielectric constant and the water content is debye-koer double-dispersion dielectric model, and the dielectric characteristics of the ears, leaves and stems of paddy are simulated by using the debye-koer double-dispersion dielectric model of the dielectric constant and the water content of vegetation, so as to obtain complex dielectric constants of the paddy components under different frequencies, which are expressed as: In the above-mentioned method, the step of, Representing the non-dispersive residual portion, Representing the temperature of the product at room temperature ) The dielectric constant of free water is set, Representing the volume fraction of free water, Represents the dielectric constant of the bound water, The volume fractions of the combined water are expressed as: Wherein, the Represents the weight water content of the rice component, Representing the frequency of the electromagnetic wave, Representing the units of an imaginary number, In order to achieve the ion conductivity, The salinity is 8.5 per mill.
4. The method for simulating a radar backscatter coefficient of a rice field in a earbud period according to claim 1, wherein in step S5, the three-dimensional geometric modeling includes simulating a central axis of a rice ear with a gaussian curve, simulating a grain with an ellipsoid, simulating a blade profile with a Hermite curve, and simulating a stalk with an elongated cylinder.
5. The method for simulating the radar backscatter coefficient of a paddy field in the ear period according to claim 1, wherein the equation for calculating the attenuation coefficient in step S7 is: Wherein, the Indicating the polarization mode of the transmitted and received electromagnetic waves, Representing the wave number in free space, Represents the irradiation area of the radar wave, And The attenuation coefficients of the L1 layer and the L2 layer are respectively indicated, 、、 Respectively representing the numbers of ears, leaves and stems in the corresponding layers, 、、 Respectively represent the propagation direction of the spike, leaf and stem along the electromagnetic wave The (a) represents the statistical averaging operation, Representing imaginary units, thereby calculating propagation constants of electromagnetic waves in the L1 layer and the L2 layer Expressed as: 。
6. The method for simulating the radar backscatter coefficients of the paddy field with spike period according to claim 1, wherein in the step S8, the spatial simulation is specifically that the uniform row-column distribution of the paddy plants is determined by taking piers as units, single plants are randomly distributed in each pier, a plant local coordinate system is established by taking spike points as origin points, and finally the system is converted into a global coordinate system.
7. The method for modeling a rice field radar backscatter coefficient of a rice field with spike period according to claim 1, wherein in step S9, the phase offset is calculated based on a combination of lengths of four basic propagation paths: Wherein, the In units of imaginary numbers, And The attenuation coefficients of the L1 layer and the L2 layer are respectively indicated, Representing the spatial position vector of the components in the canopy of the paddy field, Representing the direction vector of the incident wave in free space, Representing the unit direction vector of the incident wave Edge of the frame The component of the shaft is used to determine, And representing the incident angle, and calculating the phase offset at the positions of different components in the canopy according to the simulated spatial positions of the components in the canopy.
8. The method for simulating the radar back-scattering coefficient of a rice field with spike period according to claim 1, wherein in step S10, the coherent superposition of the scattered electric fields is performed by using coherent superposition approximation, and the total radar back-scattering electric field is expressed as: Wherein, the Represents a natural constant of the natural product, Representing the distance from the radar antenna phase center to the paddy field scene, Represents the components of the ear, the leaf and the stem, Representing the scattering matrix of the different components, Indicating the direction of the incident electromagnetic wave, Indicating the direction of the scattered electromagnetic wave, Representing the corresponding angle of incidence And Fresnel reflection coefficient at polarization.
9. The method for simulating radar back scattering coefficient of paddy field in ear period according to claim 1, wherein in step S11, the final simulation results in radar back scattering coefficient of paddy field in ear period: 。
10. a system for implementing the method of any one of claims 1-8, comprising: the data acquisition and processing module is used for acquiring and processing the paddy field actual measurement parameters; the layering and decomposing module is used for executing layering of the canopy and decomposition of the scattering mechanism; the dielectric and geometric modeling module is used for simulating dielectric characteristics of the component and constructing a three-dimensional geometric model; the electromagnetic simulation module is used for simulating and calculating the scattering matrix of each component; The attenuation calculation module is used for calculating the attenuation coefficient and propagation constant of the electromagnetic wave in the canopy; the space position simulation module is used for simulating the space distribution position of each component in the paddy field; the phase offset calculation module is used for calculating phase offset under each scattering path; The scattering synthesis and coefficient calculation module is used for synthesizing the total scattering electric field and calculating a backscattering coefficient; the verification and evaluation module is used for comparing the simulation result with the actual measurement data and evaluating the precision; the electromagnetic simulation module is integrated with a FEKO or HFSS electromagnetic simulation software interface.

Description

Method and system for simulating rice field radar backscattering coefficient in ear period Technical Field The invention relates to the technical field of agricultural remote sensing and information, in particular to a method and a system for simulating a radar backscattering coefficient of a paddy field in a spike period. Background Rice is one of three grain crops worldwide, and has very important proportion in grain structures in China. The rice grows in cloudy and rainy areas, and the synthetic aperture radar has the advantages of all-weather, penetrability and the like, and provides an important technical means for large-scale rice monitoring. The radar backscattering coefficient is one of the most commonly used parameters for rice monitoring, the accurate simulation is a precondition for correctly understanding the rice canopy microwave scattering mechanism, and the radar backscattering coefficient is a basis for remote sensing quantitative application such as rice mapping, parameter inversion (such as leaf area index, biomass, canopy height) and yield estimation. As a basic scattering unit of a paddy field, the geometric form and structural characteristics of ears, leaves and stems are complex, a traditional radar backward scattering coefficient simulation method is used for modeling a paddy component by using a simple geometric body (such as a cylinder, an elliptic disc and a rectangular sheet), then the scattering field is obtained by approximate calculation of an electromagnetic scattering theory, and the modeling is simplified to enable the paddy component to deviate from the actual form, in particular the paddy ear. As the most important component of rice, the rice spike parameter has stronger correlation with the radar backscatter coefficient of a rice field scene, but the modeling of the rice spike is not considered much in the existing method, and the modeling of the rice spike is often too simplified (such as a cylinder), so that the simulation precision of the electromagnetic scattering characteristic of the rice spike is also lower, and further, the simulation precision of the radar backscatter coefficient of the rice field in the spike period is not high. Therefore, by establishing a three-dimensional geometric model of key components (such as ears, leaves and stems) of rice, fine modeling is carried out on the complex geometric structure of the rice components, particularly the rice ears, electromagnetic scattering characteristics of the rice components under different parameter combinations (such as wave bands, polarization, incidence angles and azimuth angles) are solved, the propagation and scattering processes of electromagnetic waves in rice crowns and attenuation characteristics are simulated by fusing electromagnetic simulation results and radiation transmission equations of different components, and finally high-precision simulation of the radar backscattering coefficients of the rice in the ear stage is realized. The rice field radar backscattering coefficient is mainly obtained by three modes, namely a microwave scattering model, a measurement experiment and electromagnetic simulation. (1) The microwave scattering model starts from an electromagnetic scattering theory, and a strict mathematical physical method is utilized to establish a functional relation between a radar backscattering coefficient and a rice geometric physiological parameter. Although the method has better universality, the geometric structure of the rice component is characterized and distorted due to the simplification of the modeling of the rice component, so that the electromagnetic scattering characteristic simulation result of the component is low in accuracy, and the method is a key factor for limiting the simulation accuracy of the backward scattering coefficient of the rice radar. (2) The measurement experiment extracts the rice field radar backscattering coefficient from the scatterometer measurement or SAR imaging result, so that a more reliable result can be obtained, but most of measurement sensors work under specific wave bands, polarization and incidence angles, only observation data under limited parameter combinations can be obtained, and the measurement experiment focuses on large-scale scene observation, so that the accurate measurement of rice plants and components is difficult to carry out by the existing measurement means and resolution. (3) Electromagnetic simulation starts from three-dimensional modeling of the rice component, electromagnetic solution is directly carried out on three-dimensional models of the rice component, plants and scenes, the target with any complex shape can be simulated and calculated, and the calculation result can reach industrial-level precision. The three-dimensional model of the rice scene can be regarded as an electric large-size target (relative to the wavelength), and the calculated amount and the memory requirement are large when electromagnetic simulati