CN115219795A - Dielectric constant model construction method suitable for microwave inversion of soil moisture - Google Patents

Dielectric constant model construction method suitable for microwave inversion of soil moisture Download PDF

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CN115219795A
CN115219795A CN202210844179.3A CN202210844179A CN115219795A CN 115219795 A CN115219795 A CN 115219795A CN 202210844179 A CN202210844179 A CN 202210844179A CN 115219795 A CN115219795 A CN 115219795A
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dielectric constant
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saline
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宋小宁
高亮
马建威
冷佩
胡容海
王艳芬
李小涛
周芳成
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University of Chinese Academy of Sciences
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Abstract

The invention provides a dielectric constant model construction method suitable for microwave inversion of soil moisture, which comprises the following steps of extracting soil salinity data: constructing an improved saline soil dielectric constant model, and dividing the optimized saline soil dielectric constant model into two-stage models, wherein the two-stage models comprise a high-salinity saline soil dielectric constant model and a low-salinity saline soil dielectric constant model; respectively bringing the soil salinity data into the high salinity saline soil dielectric constant model and the low salinity saline soil dielectric constant model according to a salinity division rule, and calculating the dielectric constant of the brine; and (4) substituting the dielectric constant of the saline water into a Dobson model to obtain the dielectric constant of the saline soil. The invention provides a dielectric constant model construction method suitable for microwave inversion of soil moisture, which is used for correcting an original model to a certain extent and providing a saline soil dielectric constant model suitable for a larger application range.

Description

Dielectric constant model construction method suitable for microwave inversion of soil moisture
Technical Field
The invention relates to the technical field of microwave remote sensing, in particular to a dielectric constant model construction method suitable for microwave inversion of soil moisture.
Background
Soil moisture is one of the important surface environmental parameters. The soil moisture data set has important significance for the application and research of crop growth vigor, yield evaluation, ecological environment, climate change monitoring and the like. The microwave inversion method is a main way for efficiently obtaining a spatially continuous soil moisture product with high space-time resolution. In the process of inverting the soil moisture by microwave remote sensing, firstly, a soil dielectric constant is obtained through a bright temperature or a backscattering coefficient observed by a satellite; secondly, soil moisture content information is estimated on the basis of other auxiliary data and the dielectric constant. The soil dielectric constant model generally constructs a quantitative relation between the soil dielectric constant and soil properties such as soil water content, soil salinity, soil texture, microwave frequency and the like, and is a main component of the method for inverting the soil moisture by microwave remote sensing. Currently, there have been many studies on the dielectric properties of soil and a soil dielectric constant model has been established. However, existing models are still less accurate at high moisture content or high salinity conditions. In soil moisture inversion, soil salinity information is considered by a few inversion methods because the regional scale soil salinity spatial distribution data is difficult to obtain. Researches show that the salinity change of the soil has great influence on the dielectric constant, and further influences the backscattering coefficient and the brightness temperature of the soil. Therefore, the soil moisture inversion method based on microwave data has a great uncertainty due to the influence of salinity data and the dielectric constant of saline soil. In order to improve the accuracy of soil moisture inversion, the accuracy of the existing saline soil dielectric constant model needs to be improved.
The current saline soil dielectric constant models comprise a Dobson-s model, an HQR model, a WYR model and the like. The models establish a semi-empirical relationship among the water content, the salt content and the dielectric constant of the soil, and a soil dielectric constant model is initially established for soil moisture inversion based on microwave data on the basis of theoretical derivation and a large amount of measured data. However, the current classical models of the dielectric constant of saline soils still have many deficiencies. First, studies have shown that the Dobson-s model has an underestimation of the imaginary part of the permittivity, and that soil salinity primarily acts on the imaginary part of the permittivity, which underestimates the effect of salinity on the imaginary part of the permittivity of saline soils. The HRQ model has a good simulation effect on the dielectric constant of the soil with high salinity, however, when the salinity of the soil is low, the model has a large error on the simulation of the complex dielectric constant of the saline soil. Compared with the two models, the WYR model has a larger application range, but the dielectric constant simulation precision of the model on the high-salinity soil is lower. In summary, the existing dielectric constant model of the saline soil cannot realize a dielectric constant model of the saline soil in a larger range of soil water content and salt content, and further improvement on the existing dielectric constant model is needed.
Disclosure of Invention
In order to solve the technical problems, the invention provides a dielectric constant model construction method suitable for microwave inversion of soil moisture, which corrects an original model to a certain extent and provides a saline soil dielectric constant model suitable for large soil moisture and salinity ranges.
The invention provides a method for constructing a dielectric constant model suitable for microwave inversion of soil moisture, which comprises the following steps of extracting soil salinity data:
step 1: constructing an improved saline soil dielectric constant model, and dividing the optimized saline soil dielectric constant model into two-stage models, wherein the two-stage models comprise a high-salinity saline soil dielectric constant model and a low-salinity saline soil dielectric constant model;
and 2, step: according to a salinity division rule, bringing soil salinity data into the high-salinity saline soil dielectric constant model or the low-salinity saline soil dielectric constant model, and calculating a saline water dielectric constant;
and 3, step 3: and (4) substituting the dielectric constant of the saline water into a Dobson model to obtain the dielectric constant of the saline soil.
Preferably, the soil salinity data comprises soil salinity S and volume water content m v Soil density ρ s Volume weight of soil ρ b And the texture of the soil.
In any of the above aspects, preferably, the salinity partitioning rule comprises when the soil salinity is greater than 20g/kg and the volume water content is greater than 0.3m 3 /m 3 Then, the high-salinity saline soil dielectric constant model is selected.
In any of the above embodiments, it is preferable that the soil solution concentration S in the high-salinity saline soil dielectric constant model mv And the conductivity sigma of the salt water sw A linear relationship exists between the salinity S of the soil and the volume water content m v The concentration of the soil solution is expressed to obtain the conductivity sigma of the brine sw 。
In any of the above solutions, it is preferred that the brine conductivity σ sw Is expressed as
σ sw ＝α·S wv ＝a·ρ b ·S b /m v
Where a is an empirical coefficient, ρ b Is the soil volume weight and S is the soil salinity.
In any of the above solutions it is preferred that the brine conductivity σ is adjusted sw The expression of (A) is substituted into the Debye equation to obtain the imaginary part expression of the dielectric constant of the brine as follows
Figure BDA0003751667840000031
Wherein f is the microwave frequency, τ sw As relaxation time of saline water,. Epsilon sw0 Is the static dielectric constant of brine, epsilon sw∞ Is the dielectric constant of brine at extreme frequency,. Epsilon 0 The dielectric constant of a vacuum.
In any of the above schemes, preferably, the salinity classification rule further comprises when the soil salinity is less than or equal to 20g/kgThe water content is less than or equal to 0.3m 3 /m 3 Then, the dielectric constant model of the low-salinity saline soil is selected.
In any of the above embodiments, preferably, in the low-salinity saline soil dielectric constant model, the brine conductivity σ sw And said soil salinity S, said volume water content m v Is expressed as
Figure BDA0003751667840000032
Wherein S is soil salinity.
In any of the above solutions, it is preferred that the brine conductivity σ is adjusted sw The expression of (a) is substituted into the Debye equation to obtain the imaginary part expression form of the dielectric constant of the brine as follows
Figure BDA0003751667840000033
In any of the above embodiments, preferably, the dielectric constant of the saline soil is expressed by
Figure BDA0003751667840000034
Figure BDA0003751667840000035
Wherein is epsilon' soil Is the real part of the dielectric constant, ρ, of saline soil s Is the density of soil, epsilon s Is the dielectric constant, m, of solid soil particles v Is the volume water content of soil, epsilon' sw Is the real part of the dielectric constant of salt water, epsilon' soil Is the imaginary part of the dielectric constant, epsilon, of saline soil " sw Beta 'and beta' are empirical parameters related to soil texture, as imaginary parts of the brine dielectric constant.
The invention provides a dielectric constant model construction method suitable for microwave inversion of soil moisture, and the precision of an improved evaluation model under different application conditions and the precision of a simulation result are improved.
The Dobson model is the most commonly used relational model describing the relationship between the dielectric constant of soil and the volumetric water content of soil.
The Debye equation gives a theoretical model for calculating the dielectric constant of free water, and parameters such as relaxation time of water, static dielectric constant of water, dielectric constant of water under extreme frequency and the like are mainly used in the model to simulate the quantitative relation between the water content of soil and the free water in the soil.
Drawings
Fig. 1 is a flowchart of a method for constructing a dielectric constant model for microwave inversion of soil moisture according to a preferred embodiment of the present invention.
Fig. 2 is a schematic diagram illustrating the dielectric constant verification of the soil with different water contents and salinity according to the method for constructing the dielectric constant model for microwave inversion of soil water in the present invention.
FIG. 3 is a schematic diagram illustrating the dielectric constant verification of soil with different water contents and salinity according to another embodiment of the method for constructing the dielectric constant model for microwave inversion of soil water in the invention.
FIG. 4 is a schematic diagram illustrating the dielectric constant verification of the soil with different water contents and salinity according to the method for constructing the dielectric constant model for microwave inversion of soil water in the invention.
Detailed Description
The invention is further illustrated by the following detailed description of embodiments in connection with the drawings.
Example one
As shown in FIG. 1, step 100 is performed to extract soil salinity data, which includes soil salinity S and volume water content m v Soil solution concentration S mv And brine conductivity σ sw 。
Step 110 is executed to construct an improved saline soil dielectric constant model, and the optimized saline soil dielectric constant model is divided into two-stage models, including a high-salinity saline soil dielectric constant model and a low-salinity saline soil dielectric constant model.
The salinity partitioning rule comprises:
(1) When the salinity of the soil is more than 20g/kg and the volume water content is more than 0.3m 3 /m 3 And selecting the high-salinity saline soil dielectric constant model.
(2) When the salinity of the soil is less than or equal to 20g/kg or the volume water content is less than or equal to 0.3m 3 /m 3 Then, the dielectric constant model of the low-salinity saline soil is selected.
And step 120, carrying out salinity classification rules to bring the soil salinity data into the high salinity saline soil dielectric constant model or the low salinity saline soil dielectric constant model, and calculating the saline water dielectric constant.
In the high-salinity saline soil dielectric constant model, the concentration S of the soil solution mv And the conductivity σ of the salt water sw A linear relationship exists between the salinity S of the soil and the volume water content m v The concentration of the soil solution is expressed to obtain the conductivity sigma of the brine sw . Brine conductivity σ sw Is expressed as
σ sw ＝α·S wv ＝α·ρ b ·S b /m v
Where α is an empirical coefficient, ρ b Is the soil volume weight and S is the soil salinity.
Conductivity sigma of the brine sw The expression of (A) is substituted into the Debye equation to obtain the imaginary part expression of the dielectric constant of the brine as follows
Figure BDA0003751667840000051
Wherein f is the microwave frequency, τ sw As saline relaxation time, epsilon sw0 Is the static dielectric constant of brine, epsilon sw∞ Is the dielectric constant of brine at extreme frequency,. Epsilon 0 The dielectric constant of a vacuum.
In the low-salinity saline soil dielectric constant model, the conductivity sigma of the saline water sw And said soil salinity S, said volume water content m v Is expressed as
Figure BDA0003751667840000052
Wherein S is soil salinity, a and b are empirical coefficients, m v The volumetric water content of the soil.
Subjecting the brine to conductivity σ sw The expression of (a) is substituted into the Debye equation to obtain the imaginary part representation of the dielectric constant of the brine as follows:
Figure BDA0003751667840000053
step 130 is executed, the dielectric constant of the saline water is brought into the Dobson model to obtain the dielectric constant of the saline soil, and the expression of the dielectric constant of the saline soil is
Figure BDA0003751667840000061
Figure BDA0003751667840000062
Wherein is epsilon' soil Is the real part of the dielectric constant of the saline soil, rho s Is the density of soil, epsilon s Is the dielectric constant of saline soil, m v Is volume water content, epsilon' sw Is the real part of the dielectric constant of brine,. Epsilon' soil Is the imaginary part of the dielectric constant, epsilon, of saline soil " sw As the imaginary part of the dielectric constant of brine, β "and β' are empirical parameters related to soil texture.
Example two
The invention further improves the existing model on the basis of the actual measurement data and the existing model to obtain a semi-empirical dielectric constant model which has wider application range and better simulation effect on the dielectric constant of the soil. The model has important significance for recognizing the dielectric property of the soil and quantitatively monitoring the physicochemical property of the soil. On the basis of the model obtained by the invention, the influence of salinity can be further considered in the soil moisture inversion method taking microwave remote sensing as main data, and the model with higher inversion result precision is obtained; or on the basis of adding other auxiliary data or improving the research method, the cooperative inversion of the soil salinity and the soil moisture can be realized.
The invention relates to an improved model of the existing saline soil dielectric constant model. When the existing saline soil dielectric constant model is used for simulating the dielectric constant of soil with higher soil moisture content and salinity content, the precision of a simulation result is reduced. Aiming at the defects of the original model, the invention modifies the original model to a certain extent and provides a saline soil dielectric constant model which is applicable to a larger application range.
The effect of salinity on the dielectric constant is mainly reflected in that the salinity of the soil has a significant influence on the imaginary part of the dielectric constant of the soil. The first is the influence of salinity on the imaginary part of the dielectric constant of saline water, which is shown in the following that the salinity of soil is related to the concentration of soil solution, the concentration of soil solution is strongly related to the conductivity, and the conductivity of soil affects the imaginary part of the dielectric constant. The research shows that the soil has different dielectric properties under different conditions, and the response of the saline soil dielectric constant to salinity and the volume water content of the soil is greatly different. Therefore, the invention uses the assumption in the classical saline soil dielectric constant model for reference, and 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.
When the salinity S of the soil is more than 20g/kg and the volume water content m v Greater than 0.3m 3 /m 3 Time, soil solution concentration S mv And brine conductivity σ sw There is a linear relationship between them. Further, the salinity S and the volume water content m of the soil are utilized v And (3) expressing the concentration of the soil solution to obtain the conductivity of the saline water, wherein the specific expression is shown as the formula (1).
σ sw ＝a·S wv ＝a·ρ b ·S b /m v (1)
The expression of the conductivity of the saline water is introduced into the Debye equation, and the imaginary part of the dielectric constant of the saline water is expressed as follows:
Figure BDA0003751667840000071
when the salinity of the soil is less than or equal to 20g/kg or the volume water content is less than or equal to 0.3m 3 /m 3 Conductivity of brine sigma sw And soil salinity S, volume water content m v The empirical relationship between them is shown in formula (3), and the imaginary part of the dielectric constant of salt water is shown in formula (4)
Figure BDA0003751667840000072
Figure BDA0003751667840000073
Wherein the saline relaxation time τ sw Dielectric constant epsilon of salt water under extreme frequency sw∞ The expression form of (A) is given by Stogryn and Klein models, and the static dielectric constant epsilon of saline water sw0 Has the same value as that of pure water.
Salinity has important influence on the effective conductivity of the brine, and the model quantitatively constructs the correlation between the salinity and the effective conductivity of the brine to obtain a quantitative model between the imaginary part of the dielectric constant of the brine and the salinity. Then, the dielectric constant of the saline water is brought into a Dobson model (shown as formulas (5) and (6)) to obtain the dielectric constant of the saline soil.
Figure BDA0003751667840000074
Figure BDA0003751667840000075
EXAMPLE III
The invention aims to improve the simulation precision of the saline soil dielectric constant model on the relationship between the saline soil dielectric constant and the physical properties of soil. In order to illustrate the effect of the present invention and the improvement of the model, the model is verified based on the existing data and is compared and analyzed with the existing WYR model with the highest precision. As shown in FIG. 2, the invention evaluates the accuracy of the model under different application conditions and improves the accuracy of the simulation result through respective verification under different salinity and water content conditions.
The invention greatly improves the simulation effect of the dielectric constant model, the RMSE of the model is 1.628, R is 2 Is 0.918. From the verification figure, 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 line 1.
Meanwhile, on the basis of the verification of the collected measured data, the model obtained by the method is compared and analyzed with other models, and the verification result is shown in fig. 3.
The verification result shows that the dielectric constant of the soil obtained by the model simulation is greatly improved in each soil moisture interval relative to the original model. In the range of 0.05-0.4m 3 /m 3 The RMSE of the simulation results was generally less than 2.5 over the range of soil moisture intervals. Meanwhile, in 5 soil moisture intervals in fig. 3, the precision of the model simulation result is greatly improved, and the RMSE of the soil dielectric constant simulation result in each moisture interval is reduced to a certain extent compared with that of the original model. Compared with the WYR model, the model obtained by the invention has the most remarkable improvement on the simulation precision of the soil dielectric constant with higher soil moisture content, and the concrete expression is that when the soil moisture is more than 0.1m 3 /m 3 When the RMSE of the WYR model is more than 2.5, the soil moisture of the model obtained by the invention is from 0.05 to 0.40m 3 /m 3 The RMSE of the simulated dielectric constant was less than 2.5 throughout the moisture study range. Meanwhile, the model obtained by the method has the same trend with the original model in different soil water content intervals. Specifically, the higher the soil moisture, the larger the RMSE of the dielectric constant, and the lower the accuracy of the simulated dielectric constant.
The invention also verifies the simulation capability of the obtained model on the dielectric constant of the soil in different salinity ranges. The verification result shows that the response capability of the model simulation dielectric constant on salinity is greatly improved. Firstly, as shown in FIG. 4, at each soil salinity level within the whole salinity research range of 3-100g/kg, the simulation capability of the model obtained by the invention on the soil dielectric constant is greatly improved; secondly, when the salinity of the WYR model is more than 20g/kg, the RMSE of the simulated dielectric constant is larger, the dielectric constant simulation performance of the model obtained by the method is greatly improved under the condition of high salinity, and the RMSE of the model is less than 2.5 in the whole salinity grade range.
For a better understanding of the present invention, the foregoing detailed description has been given in conjunction with specific embodiments thereof, but not with the intention of limiting the invention thereto. Any simple modifications to the above embodiments in accordance with the technical spirit of the present invention are within the scope of the technical solution of the present invention. In the present specification, each embodiment is described with emphasis on differences from other embodiments, and the same or similar parts between the respective embodiments may be referred to each other. For the system embodiment, since it basically corresponds to the method embodiment, the description is relatively simple, and for the relevant points, reference may be made to the partial description of the method embodiment.

Claims (10)

1. A dielectric constant model construction method suitable for microwave inversion of soil moisture comprises the steps of extracting soil salinity data, and is characterized by further comprising the following steps:
step 1: constructing an improved saline soil dielectric constant model, and dividing the optimized saline soil dielectric constant model into two-stage models, wherein the two-stage models comprise a high-salinity saline soil dielectric constant model and a low-salinity saline soil dielectric constant model;
and 2, step: according to a salinity division rule, bringing soil salinity data into the high-salinity saline soil dielectric constant model or the low-salinity saline soil dielectric constant model, and calculating a saline water dielectric constant;
and step 3: and (4) substituting the dielectric constant of the saline water into a Dobson model to obtain the dielectric constant of the saline soil.
2. The method for constructing the dielectric constant model suitable for microwave inversion of soil moisture according to claim 1, wherein the soil salinity data comprises soil salinity S and volume water content m v 。
3. The method for constructing the dielectric constant model suitable for microwave inversion of soil moisture according to claim 2, wherein the salinity division rule comprises that when the soil salinity is more than 20g/kg and the volume water content is more than 0.3m 3 /m 3 And selecting the high-salinity saline soil dielectric constant model.
4. The method for constructing the dielectric constant model suitable for microwave inversion of soil moisture according to claim 3, wherein in the high-salinity saline soil dielectric constant model, the soil solution concentration S is mv And the conductivity sigma of the salt water sw A linear relationship exists between the salinity S of the soil and the volume water content m v The concentration of the soil solution is expressed to obtain the conductivity sigma of the brine sw 。
5. The method for constructing a dielectric constant model suitable for microwave inversion of soil moisture according to claim 4, wherein the brine conductivity σ is sw Is expressed as
σ sw ＝a·S wv ＝a·ρ b ·S b /m v
Where α and b are empirical coefficients, ρ b Is the soil volume weight, and S is the soil salinity.
6. The method for constructing the dielectric constant model for microwave inversion of soil moisture according to claim 5, wherein the brine conductivity σ is determined sw The expression of (a) is substituted into the Debye equation to obtain the imaginary part representation of the dielectric constant of the brine as follows:
Figure FDA0003751667830000021
wherein f is the microwave frequency, τ sw As relaxation time of saline water,. Epsilon sw0 Is the static dielectric constant of brine,. Epsilon sw∞ Dielectric constant of brine at extreme frequency,. Epsilon 0 The dielectric constant of a vacuum.
7. The method for constructing the dielectric constant model suitable for microwave inversion of soil moisture according to claim 6, wherein the salinity classification rule further comprises that when the soil salinity is less than or equal to 20g/kg or the volume water content is less than or equal to 0.3m 3 /m 3 Then, the dielectric constant model of the low-salinity saline soil is selected.
8. The method for constructing the dielectric constant model suitable for microwave inversion of soil moisture according to claim 7, wherein in the low-salinity saline soil dielectric constant model, the brine conductivity σ is sw And said soil salinity S, said volume water content m v Is expressed as
Figure FDA0003751667830000022
Wherein S is soil salinity.
9. The method for constructing a dielectric constant model suitable for microwave inversion of soil moisture according to claim 8, wherein the brine conductivity σ is determined sw The expression of (A) is substituted into the Debye equation to obtain the imaginary part expression of the dielectric constant of the brine as follows
Figure FDA0003751667830000023
10. The method for constructing the dielectric constant model suitable for microwave inversion of soil moisture according to claim 9, wherein the expression of the dielectric constant of the saline soil is
Figure FDA0003751667830000024
Figure FDA0003751667830000025
Wherein is epsilon' soil Is the real part of the dielectric constant, ρ, of saline soil s Is the true density of the soil, epsilon s Dielectric constant of solid particles of soil, m v Is the volume water content of the soil, epsilon' sw Is the real part of the dielectric constant, ε, of brine " soil Is the imaginary part of the dielectric constant, epsilon, of saline soil " sw Being the imaginary part of the dielectric constant of brine, β "and β' are empirical parameters related to soil composition.
CN202210844179.3A 2022-07-18 2022-07-18 Dielectric constant model construction method suitable for microwave inversion of soil moisture Pending CN115219795A (en)

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN117609686A (en) * 2024-01-23 2024-02-27 云南农业大学 Soil moisture content evaluation method based on frequency domain dielectric spectrum

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN117609686A (en) * 2024-01-23 2024-02-27 云南农业大学 Soil moisture content evaluation method based on frequency domain dielectric spectrum
CN117609686B (en) * 2024-01-23 2024-04-12 云南农业大学 Soil moisture content evaluation method based on frequency domain dielectric spectrum

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