Study On Microwave Dielectric Model Of Saline Soil

Soil salinization is one of the main causes of environmental damage.Soil salinization will affect soil properties,and lead to soil degradation and productivity decline in agricultural areas,thus jeopardizing China's food security.In order to quickly monitor the area and degree of soil salinization in large areas,remote sensing technology has been developed.Compared with visible light and infrared remote sensing,microwave remote sensing has more advantages in monitoring saline soil.Due to the electromagnetic wave penetrating to a certain extent,microwave remote sensing can be all-weather,all-day access to data.Just as optical remote sensing needs to establish a specific absorption spectrum of saline soil types when identifying saline soil information,microwave remote sensing also needs to establish a functional model between soil texture,water content,salt content and soil dielectric response when identifying saline soil types and inverting saline and water content.Dielectric constant is an important parameter for microwave remote sensing inversion.It can not only directly invert the soil moisture content,but also directly invert the soil salinity through the dielectric constant,so as to accurately obtain the soil moisture and salinity information.At present,there are HQR model,WYR(C-band)model and so on for microwave dielectric models of saline soil.However,these models are all soil samples prepared with a single Na Cl solution in the laboratory to study and obtain the microwave dielectric model of saline soil.The model itself still has limitations.These models are not suitable for the inversion of salt content and water content of soda-saline and sulphate-saline soils in arid and semi-arid regions.Therefore,it is a key technology for dynamic monitoring and prediction of salinized land area,soil drought degree and salinization degree to establish a universally applicable microwave dielectric model which can accurately and quantitatively invert water content and salt content of saline soil.The purpose of this paper is to study the microwave dielectric properties of different types of saline soils,and to establish a microwave(1.43GHz)dielectric(TSS)model suitable for different types of saline soils.For this purpose,the main research contents and methods of this paper are as follows:1.In this experiment,the dielectric constants of the prepared chlorine salt,sulfate and soda salt soil solutions as well as the electrolyte solutions of Na Cl,Na HCO₃ and Na₂SO₄ were measured with an L-band resonator,and the complex influence factors of Na⁺,Cl^-,SO₄^2-,CO₃^2-and HCO₃^-were given.Based on the Collie dielectric model,the influence factors of a single aqueous solution of Na Cl,Na HCO₃ and Na₂SO₄ were used to replace the complex influence factors of complex chloride,sulfate and soda salt soil solutions,respectively.The study of this model will lay the foundation for simplifying the estimation of the total salinity of complex ions in various types of saline soils,and for the study of microwave dielectric models of different types of saline soils.2.Three types of salt solutions(Na Cl,Na HCO₃ and Na₂SO₄)were prepared in the laboratory and different concentrations and types of salt solutions were added to the collected field soil samples.The prepared saline soil types were mainly divided into three types of saline soil,namely chlorine salt,sulfate and soda salt,and the water content and salt content of the soil samples were six different gradients.The dielectric constants of prepared samples of water-bearing saline soil and saline solution were measured with a 1.43GHz resonator at different temperatures.On the basis of Dobson's semi-empirical model,the TSS microwave dielectric model was developed to invert the salinity and moisture information of chloride,soda and sulfate saline soils.3.Regarding the test of TSS model of chloride saline soil,the TSS model was compared with the HQR model of soil samples prepared from Na Cl solution,and the accuracy of inversion of the water content and salt content of chloride saline soil by two models was studied.For the TSS model test of soda and sulfate saline soil,this paper compared the dielectric constant of saline soil samples collected in the field by resonant cavity measurement,and analyzes the accuracy of the TSS model to invert the water content and salinity of soda and sulfate saline soil.Through comparative analysis,the HQR model is only suitable for the inversion of salinity of chlorine-saline soil with high salinity and water content,while the TSS model is suitable for the quantitative inversion of moisture and salinity of three types of saline soil.The sensitivity equation can be used to estimate the accuracy of the L-band microwave radiometer in the inversion of salinity and humidity of saline soil at a certain sensitivity level.4.The TSS microwave dielectric model given in this paper not only has high inversion accuracy,but also has self-consistent and symmetrical properties.When the soil salinity tends to 0,the soil solution salinity also tends to 0,and then the salt ion influence constants _s??and _s??in the soil solution also tend to 0.At this time,the TSS model is reduced to the Dobson model,which is mutually consistent.When the soil is full salt,that is,when S=1,S_mv becomes the amount only related to water content and bulk density,which is consistent with the objective existence of fact.Therefore,the TSS model is self-consistent.5.The TSS model is a dielectric model based on the 1.43 GHz frequency point that is more sensitive to salinity.The full-band dielectric model needs further research.It should be further pointed out that the TSS model is open,and some of its parameters need further research,verification and improvement in the application.