A dielectric constant model construction method suitable for microwave inversion of soil moisture
By constructing a two-stage dielectric constant model for saline soil with high and low salinity, the problem of insufficient accuracy of existing models under high moisture and high salinity conditions is solved, and high-precision soil dielectric constant simulation is achieved over a wide range.
Patent Information
- Application Number
- CN202210844179.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-07-18
- Publication Date
- 2026-01-16
- Estimated Expiration
- 2042-07-18
AI Technical Summary
Existing models for the dielectric constant of saline soils have low accuracy under conditions of high moisture content or high salinity, and cannot accurately simulate the dielectric constant of soils over a wide range of soil moisture and salinity, especially for soils with high salinity.
An improved dielectric constant model for saline soil was constructed, which was divided into two stages: high salinity and low salinity. Soil salinity data were incorporated into the corresponding models using different salinity classification rules. The dielectric constant of saline soil was calculated using the Debye equation. The Dobson model was then modified to improve its accuracy by combining parameters such as soil salinity, volumetric water content, and soil texture.
The accuracy of the dielectric constant model was significantly improved under different application conditions. The simulation results are closer to the measured data, the RMSE is reduced, and the R2 is improved. The simulation accuracy is particularly significantly improved under high salinity and high moisture conditions.
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Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of microwave remote sensing, and particularly relates to a dielectric constant model construction method suitable for microwave inversion of soil moisture. BACKGROUND
[0002] Soil moisture is one of the important land surface environment parameters. Soil moisture dataset is of great significance for crop growth, yield estimation, ecological environment and climate change monitoring applications and research. Microwave inversion method is the main way to obtain spatially continuous high spatio-temporal resolution soil moisture products. In the process of microwave remote sensing inversion of soil moisture, firstly, the soil dielectric constant is obtained through the satellite observed brightness temperature or backscattering coefficient; secondly, the soil moisture content information is estimated on the basis of other auxiliary data and dielectric constant. The soil dielectric constant model usually constructs the quantitative relationship between soil dielectric constant and soil moisture content, soil salinity, soil texture and microwave frequency, and is the main component of the microwave remote sensing inversion method of soil moisture. At present, there are many studies on the dielectric properties of soil and the establishment of soil dielectric constant model. However, the existing model still has low accuracy under the condition of high moisture content or high salinity. In the inversion of soil moisture, due to the difficulty in obtaining regional scale soil salinity spatial distribution data, few inversion methods consider soil salinity information. Studies have shown that the change of soil salinity content has a great influence on the dielectric constant, which further affects the backscattering coefficient and brightness temperature of soil. Therefore, due to the influence of salinity data and saline soil dielectric constant, the soil moisture inversion method based on microwave data has great uncertainty. In order to improve the accuracy of soil moisture inversion, it is necessary to improve the accuracy of the existing saline soil dielectric constant model.
[0003] The current salt soil dielectric constant model has Dobson-s model, HQR model and WYR model and the like. These models establish the semi-empirical relationship among soil water content, salt content and dielectric constant, and on the basis of theoretical derivation and a large number of measured data, the soil dielectric constant model is preliminarily established for soil moisture inversion based on microwave data. However, the current classic salt soil dielectric constant model still has many deficiencies. Firstly, research shows that the Dobson-s model has a low estimation phenomenon for the imaginary part of the dielectric constant, and the soil salinity mainly acts on the imaginary part of the dielectric constant, which underestimates the influence of salinity on the imaginary part of the dielectric constant of salt soil. The HRQ model has a good simulation effect on the dielectric constant of soil with high salt content, however, when the soil salt content is low, the model has a large error in simulating the complex dielectric constant of salt soil. Compared with the above two models, the WYR model has a larger applicable range, but the simulation precision of the dielectric constant of high salt content soil is low. In summary, the current salt soil dielectric constant model cannot realize the modeling of the dielectric constant of salt soil in a large range of soil water content and salt content, and the existing dielectric constant model needs to be further improved. SUMMARY
[0004] In order to solve the above technical problems, the application provides a dielectric constant model construction method suitable for microwave inversion of soil moisture, the original model is modified, and a salt soil dielectric constant model suitable for a large range of soil moisture and salinity is provided.
[0005] The application provides a dielectric constant model construction method suitable for microwave inversion of soil moisture, which comprises extracting soil salinity data, and further comprises the following steps:
[0006] Step 1: constructing an improved salt soil dielectric constant model, dividing the optimized salt soil dielectric constant model into two-stage models, including a high-salt salt soil dielectric constant model and a low-salt salt soil dielectric constant model;
[0007] Step 2: according to the salinity division rule, the soil salinity data is brought into the high-salt salt soil dielectric constant model or the low-salt salt soil dielectric constant model to calculate the salt water dielectric constant;
[0008] Step 3: the salt water dielectric constant is brought into the Dobson model to obtain the dielectric constant of salt soil.
[0009] Preferably, the soil salinity data comprises soil salinity S, volume water content m v , soil density ρ s , soil bulk density , and soil texture.
[0010] Preferably in any of the above solutions, the salinity classification rule comprises selecting the high-salinity-saline-soil dielectric constant model when the soil salinity is greater than 20 g / kg and the volumetric water content is greater than 0.3 m 3 / m 3 .
[0011] Preferably in any of the above solutions, in the high-salinity-saline-soil dielectric constant model, there is a linear relationship between the soil solution concentration S mv and the saline water conductivity σ sw , and the soil solution concentration S is expressed by the soil salinity S and the volumetric water content m v , to obtain the saline water conductivity σ sw .
[0012] Preferably in any of the above solutions, the expression of the saline water conductivity σ sw is
[0013]
[0014] wherein α is an empirical coefficient, ρ b is the soil bulk density, and S is the soil salinity.
[0015] Preferably in any of the above solutions, the expression of the saline water conductivity σ sw is substituted into the Debye equation to obtain the imaginary part of the saline water dielectric constant as follows
[0016]
[0017] wherein f is the microwave frequency, τ sw is the saline water relaxation time, ε sw0 is the saline water static dielectric constant, ε sw∞ is the saline water dielectric constant at the limiting frequency, and ε0 is the dielectric constant of vacuum.
[0018] Preferably in any of the above solutions, the salinity classification rule further comprises selecting the low-salinity-saline-soil dielectric constant model when the soil salinity is less than or equal to 20 g / kg or the volumetric water content is less than or equal to 0.3 m 3 / m 3 .
[0019] Preferably in any of the above solutions, in the low-salinity-saline-soil dielectric constant model, the expression of the saline water conductivity σ sw and the soil salinity S and the volumetric water content m v is
[0020]
[0021] wherein S is the soil salinity.
[0022] In any of the above solutions, it is preferred that the salt water conductivity σ sw The expression of the dielectric constant of the salt water is as follows by bringing the expression of the salt water conductivity σ
[0023]
[0024] In any of the above solutions, it is preferred that the expression of the dielectric constant of the salt soil is
[0025]
[0026]
[0027] wherein, is the real part of the dielectric constant of the salt soil, ρ s is the soil density, is the dielectric constant of the solid soil particles, is the volumetric water content of the soil, is the real part of the dielectric constant of the salt water, is the imaginary part of the dielectric constant of the salt soil, is the imaginary part of the dielectric constant of the salt water, and is an empirical parameter related to the soil texture.
[0028] The present application proposes a dielectric constant model construction method suitable for microwave inversion of soil moisture, and the improved evaluation model has improved precision under different application conditions and improved precision of simulation results.
[0029] The Dobson model is the most commonly used relationship model for describing the relationship between the dielectric constant of soil and the volumetric water content of soil.
[0030] The Debye equation gives a theoretical model for calculating the dielectric constant of free water, and the model mainly has parameters such as the relaxation time of water, the static dielectric constant of water, and the dielectric constant of water at the extreme frequency to simulate the quantitative relationship between the soil water content and the free water in the soil. BRIEF DESCRIPTION OF DRAWINGS
[0031] Figure 1 is a flow chart of a preferred embodiment of the dielectric constant model construction method suitable for microwave inversion of soil moisture according to the present application.
[0032] Figure 2 is a dielectric constant verification schematic diagram of an embodiment of the dielectric constant model construction method suitable for microwave inversion of soil moisture according to the present application for different water content and salinity soils.
[0033] Figure 3This is a schematic diagram illustrating the dielectric constant verification of soils with different water contents and salinity according to another embodiment of the dielectric constant model construction method for microwave inversion of soil moisture of the present invention.
[0034] Figure 4 This is a schematic diagram illustrating the dielectric constant verification of soils with different water contents and salinity according to another embodiment of the dielectric constant model construction method for microwave inversion of soil moisture of the present invention. Detailed Implementation
[0035] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.
[0036] Example 1
[0037] like Figure 1 As shown, step 100 is executed to extract soil salinity data, which includes soil salinity S and volumetric water content m. v Soil solution concentration S mv and the conductivity σ of salt water sw .
[0038] Execute step 110 to construct an improved dielectric constant model for saline soil. The optimized dielectric constant model for saline soil is divided into a two-stage model, including a dielectric constant model for high-salinity saline soil and a dielectric constant model for low-salinity saline soil.
[0039] The salinity classification rules include:
[0040] (1) When the soil salinity is greater than 20 g / kg and the volumetric water content is greater than 0.3 m³ 3 / m 3 When this is the case, the dielectric constant model of the high-salinity saline soil is selected.
[0041] (2) When the soil salinity is less than or equal to 20 g / kg or the volumetric water content is less than or equal to 0.3 m³ 3 / m 3 When this is the case, the dielectric constant model of the low-salinity soil is selected.
[0042] Execute step 120, and input the soil salinity data into the dielectric constant model of the high-salinity soil or the low-salinity soil according to the salinity classification rules to calculate the dielectric constant of the saline water.
[0043] In the dielectric constant model of high-salinity soil, the soil solution concentration S mv and the conductivity σ of the salt water sw There is a linear relationship between them, using the soil salinity S and the volumetric water content m. v The concentration of the soil solution is used to obtain the saline conductivity σ. sw Saltwater conductivity σ sw The expression is
[0044]
[0045] where, a is an empirical coefficient, p b is the soil bulk density, S is the soil salinity.
[0046] The expression of the brine conductivity s sw is brought into the Debye equation, and the imaginary part of the brine dielectric constant is expressed as follows
[0047]
[0048] where, f is the microwave frequency, t sw is the brine relaxation time, s sw0 is the brine static dielectric constant, s sw∞ is the brine dielectric constant at the extreme frequency, and s0 is the dielectric constant of vacuum.
[0049] In the dielectric constant model of low-salinity saline soil, the expression between the brine conductivity s sw and the soil salinity S, the volumetric water content m v is
[0050]
[0051] where, S is the soil salinity, a and b are empirical coefficients, the soil volumetric water content.
[0052] The expression of the brine conductivity s sw is brought into the Debye equation, and the imaginary part of the brine dielectric constant is expressed as follows
[0053]
[0054] The step 130 is performed, and the brine dielectric constant is brought into the Dobson model to obtain the dielectric constant of saline soil, and the expression of the dielectric constant of saline soil is
[0055]
[0056]
[0057] where, is the real part of the dielectric constant of saline soil, p s is the soil density, is the dielectric constant of saline soil, is the volumetric water content, is the real part of the brine dielectric constant, is the imaginary part of the dielectric constant of saline soil, is the imaginary part of the saltwater dielectric constant, and is an empirical parameter related to soil texture.
[0058] Example Two
[0059] The present application is based on measured data and existing models to further improve the existing model, and obtain a semi-empirical dielectric constant model with wider application range and better simulation effect of soil dielectric constant. The model has important significance for understanding the dielectric properties of soil and quantitatively monitoring the physicochemical properties of soil. On the basis of the model obtained in the present application, the influence of salinity can be further considered in the soil moisture inversion method based on microwave remote sensing as the main data, and a model with higher inversion result precision can be obtained; or on the basis of adding other auxiliary data or improving the research method, the collaborative inversion of soil salinity and soil moisture can be realized.
[0060] The present application is an improved model of the existing salt soil dielectric constant model. The existing salt soil dielectric constant model has reduced simulation result precision when simulating the dielectric constant of soil with high soil moisture content and salinity content. In view of the above shortcomings of the original model, the original model is modified to some extent, and a salt soil dielectric constant model applicable in a larger application range is proposed.
[0061] The effect of salinity on dielectric constant mainly reflects in that the soil salt content has a significant influence on the imaginary part of the soil dielectric constant. First, the influence of salinity on the imaginary part of the dielectric constant of salt water, which is specifically reflected in that the size of soil salinity is related to the concentration of soil solution, the concentration of soil solution has a strong correlation with the electrical conductivity, and the soil electrical conductivity affects the size of the imaginary part of the dielectric constant. Existing researches have shown that soil has different dielectric properties under different conditions, and the response of salt soil dielectric constant to salinity and soil volume water content has great difference. Therefore, the present application borrows the assumption in the classical salt soil dielectric constant model that the dielectric constant has different responses to salinity under different salinity conditions. When the soil contains different salinity grades, a two-stage model is set.
[0062] When the soil salinity S is greater than 20 g / kg and the volume water content m v is greater than 0.3 m 3 / m 3 , the soil solution concentration S mv and the salt water electrical conductivity σ sw have a linear relationship. Further, the soil salinity S and the volume water content m v are used to represent the soil solution concentration, and the salt water electrical conductivity is obtained, and the specific expression is as formula (1).
[0063] (1)
[0064] The improved saltwater conductivity expression is brought into the Debye equation to obtain the imaginary part of the saltwater dielectric constant as follows:
[0065] (2)
[0066] When the soil salinity is less than or equal to 20 g / kg or the volumetric water content is less than or equal to 0.3 m 3 / m 3 , the empirical relationship between the saltwater conductivity σ sw and the soil salinity S and the volumetric water content m v is as shown in equation (3), and the expression of the imaginary part of the saltwater dielectric constant is as shown in equation (4)
[0067] (3)
[0068] (4)
[0069] wherein the expression of the saltwater relaxation time τ sw and the saltwater dielectric constant ε sw∞ at the extreme frequency is given by the Stogryn and Klein models, and the saltwater static dielectric constant ε sw0 and the dielectric constant of pure water have the same value.
[0070] The salinity has an important influence on the effective conductivity of saltwater, the model quantitatively constructs the correlation between the salinity and the effective conductivity of saltwater, and obtains a quantitative model between the imaginary part of the saltwater dielectric constant and the salinity. Then, the saltwater dielectric constant is brought into the Dobson model (as shown in equations (5) and (6)) to obtain the dielectric constant of the saline soil.
[0071] (5)
[0072] (6)
[0073] Example Three
[0074] The present application aims to improve the simulation accuracy of the model of the dielectric constant of saline soil on the relationship between the dielectric constant of saline soil and the soil physical properties. In order to illustrate the effect of the present application and the improvement of the model, the model is verified on the basis of the existing data, and a comparative analysis is made with the WYR model which has the highest accuracy at present. As shown in the table, the present application is verified under different salinity and water content conditions, the accuracy of the model under different application conditions is evaluated, and the improvement of the simulation result accuracy is evaluated. Figure 2
[0075] The simulation effect of the dielectric constant model is greatly improved by the present application, the RMSE of the model is 1.628, and the R 2 is 0.918. It can be seen from the verification graph that the soil dielectric constant simulated by the model is very close to the measured data, and the distribution trend is the same, and is approximately distributed near the 1:1 line.
[0076] Meanwhile, on the basis of collecting the measured data for verification, the model obtained by the application and other models are compared and analyzed, and the verification results are shown in Figure 3
[0077] The verification results show that the soil dielectric constant simulated by the model obtained by the application has a greater improvement relative to the original model in each soil moisture interval. In the soil moisture interval range of 0.05-0.4 m 3 / m 3 , the RMSE of the simulation result is generally less than 2.5. Meanwhile, in the five soil moisture intervals in Figure 3 , the accuracy of the model simulation result is greatly improved, and the RMSE of the soil dielectric constant simulation result in each moisture content interval is reduced compared with the original model. Compared with the WYR model, the simulation accuracy of the soil dielectric constant of the model obtained by the application is most significantly improved for the soil with a higher soil moisture content, and specifically, when the soil moisture is greater than 0.1 m 3 / m 3 , the RMSE of the WYR model is greater than 2.5, and the RMSE of the model obtained by the application is less than 2.5 in the entire moisture research range of 0.05-0.40 m 3 / m 3 . Meanwhile, the same as the original WYR model, the accuracy change of the model obtained by the application and the original model in different soil moisture intervals has the same trend. Specifically, the higher the soil moisture, the greater the RMSE of the dielectric constant, and the lower the accuracy of the simulated dielectric constant.
[0078] The application also verifies the dielectric constant simulation capability of the obtained model in different salinity ranges. The verification results show that the response capability of the model simulated dielectric constant to salinity has been greatly improved. First, as shown in Figure 4 , in each soil salinity level in the entire salinity research range of 3-100 g / kg, the dielectric constant simulation capability of the model obtained by the application has been greatly improved; second, the RMSE of the dielectric constant simulated by the WYR model is larger when the salinity is greater than 20 g / kg, and the dielectric constant simulation performance of the model obtained by the application for the soil under high salinity conditions has been greatly improved, and the dielectric constant RMSE of the model is less than 2.5 in the entire salinity level range.
[0079] For better understanding of the present application, the above detailed description is made in combination with the specific embodiments of the present application, but is not a limitation to the present application. Any simple modification made to the above embodiments according to the technical essence of the present application still belongs to the scope of the technical scheme of the present application. In the specification, each embodiment focuses on the difference from other embodiments, and the same or similar parts between the embodiments can be understood by mutual reference. For the system embodiments, since they basically correspond to the method embodiments, the description is relatively simple, and the relevant parts can be understood by referring to the part of the method embodiments.
Claims
1. A method for constructing a dielectric constant model suitable for microwave inversion of soil moisture, comprising extracting soil salinity data, characterized in that, Further comprising the following steps: Step 1: constructing an improved salt soil dielectric constant model, dividing the improved salt soil dielectric constant model into a two-stage model including a high-salinity salt soil dielectric constant model and a low-salinity salt soil dielectric constant model; Step 2: according to the salinity division rule, bringing the soil salinity data into the high-salinity salt soil dielectric constant model or the low-salinity salt soil dielectric constant model to calculate the saltwater dielectric constant; The salinity division rule comprises: when the soil salinity is greater than 20 g / kg and the volumetric water content is greater than 0.3 m 3 / m 3 , the high-salinity solonchak dielectric constant model is selected. In the high-salinity solonchak dielectric constant model, there is a linear relationship between soil solution concentration S mv and saline water conductivity σ sw , and the soil salinity S and volume water content m v are used to represent the soil solution concentration, so as to obtain the saline water conductivity σ sw ; the expression of the saline water conductivity σ sw is ， where a and b are empirical coefficients, p b is the soil bulk density, S is the soil salinity; The salt water conductivity σ sw The expression of the salt water conductivity σ sw The expression of the salt water conductivity σ sw The expression of the salt water conductivity σ sw The expression of the salt water conductivity σ sw The expression of the salt water conductivity σ sw The expression of the salt water conductivity σ ， where f is the microwave frequency, τ sw is the salt water relaxation time, ε sw0 is the salt water static dielectric constant, ε sw∞ is the salt water dielectric constant at the extreme frequency, and ε0is the dielectric constant of a vacuum. The salinity division rule further comprises: when the soil salinity is less than or equal to 20 g / kg or the volume water content is less than or equal to 0.3 m 3 / m 3 , the low-salinity solonchak dielectric constant model is selected. In the low-salinity solonchak dielectric constant model, the saltwater conductivity σ sw and the soil salinity S, the volumetric water content m v is expressed as ， Wherein S is the soil salinity; The salt water conductivity σ sw The expression of the salt water conductivity σ sw The expression of the salt water conductivity σ sw The expression of the salt water conductivity σ sw The expression of the salt water conductivity σ sw The expression of the salt water conductivity σ sw The expression of the salt water conductivity σ ； The expression of the salt soil dielectric constant is ， ， wherein, is the real part of the dielectric constant of the salt water, p s is the real density of the soil, is the dielectric constant of the soil solid particles, is the volumetric water content of the soil, is the real part of the dielectric constant of the salt water, p is the imaginary part of the dielectric constant of the salt soil, is the imaginary part of the dielectric constant of the salt water, p and is an empirical parameter related to the soil composition; Step 3: bringing the saltwater dielectric constant into the Dobson model to obtain the dielectric constant of the salt soil.