盐渍土壤的微波介电模型研究

Absence of soil structure factor and thus can’t quantitatively retrieve the salinity of saline soil is the main problem of existing empirical and semi-empirical microwave dielectric models. In order to solve this problem, on the basis of the theories of dielectric phenomenological model and two channel model of soil electrical conductivity, we select typical saline soils as the sample plots, and plan to measure their dielectric constant by the free space method, and measure their conductivity, water content and temperature and other parameters by 100W.E.T soil conductivity meter in the field. And with the indoor analysis of soil texture and the analysis of the conductivity of soil soluble salts under different temperatures, we aim to study the change rule of microwave relaxation type and the static dielectric constant of saline soil with the variation of its water content and clay content. In addition, we will carry out the research of the relationship between soil electrical conductivity and soil internal geometry, temperature, moisture and salt content. Finally, based on the above research results we expect to establish a new microwave dielectric model which can be used to quantitatively retrieve the salt content and water content of saline soil. Obviously, our research work is in favor of the promotion and application of high-resolution Earth Observation System, and this model will provide critical technical support for regular dynamic monitoring and forecasting of salinization land area, salinization degree and soil drought degree. It is no doubt that our project is of great significance for the further survey and research of environmental carrying capacity as the economic development in Chinese arid and semi - arid regions.

针对现有的盐渍土的经验和半经验微波介电模型缺失土壤结构信息，不能定量反演盐渍土壤的含盐量问题，项目在电介质唯象模型和土壤电导率的二通道模型的基础上，选取典型的盐渍土作为实验样地，利用自由空间波法和土壤电导仪等设备实地测量盐渍土壤的介电常数、土壤电导率、土壤含水量和土壤温度等参数，并配合实验室的土壤质地和不同温度下的土壤可溶性盐的电导率分析，研究盐渍土壤的微波弛豫类型和静态介电常数随土壤含水量和粘土含量的变化规律，研究土壤电导率与土壤内部的几何结构、温度、含水量和含盐量的关系，并最终研究建立能够定量反演盐渍土含盐量和含水量的微波介电模型。显然，这一模型的研究，将为我国高分辨率对地观测系统的推广和应用，为微波遥感技术定期动态监测和预报盐渍化土地面积、土壤干旱程度、盐碱化程度，以及为我国干旱半干旱地区经济发展的环境承载力的调查和研究提供关键的技术支持。

以往单纯用NaCl溶液在实验室配制的土壤样品来研究盐渍土微波介电模型方法是不够充分的，其模型是不能够定量反演干旱半干旱地区苏打盐和硫酸盐盐渍土含水量和含盐量的。根据需要，项目研制了测量大损耗（tanδ≥1）盐渍土和土壤溶液介电常数的1.43GHz（TE011模）圆柱谐振腔测量系统，测量了人工配制的氯盐、硫酸盐和苏打盐土壤溶液以及NaCl、Na2SO4和NaHCO3水溶液的介电常数，并在Collie电解质水溶液介电模型的基础上，给出了Na+、Cl-、SO42-、CO32-和HCO3- 五种离子的复影响因子温度函数，研究建立了三种类型盐渍土土壤溶液的微波介电模型。这一模型的研究将为简化估算各类盐渍土复杂离子的总盐度，以及为不同类型盐渍土微波介电模型的研究奠定基础。项目又用NaCl、Na2SO4和NaHCO3溶液和田间土壤，分别配制了三种盐类型的含水含盐土壤样品，并用谐振腔测量了这些样品的介电常数。项目在Dobson半经验模型的基础上，研究建立了能够定量反演氯盐、苏打盐和硫酸盐三种盐渍土盐度和含水量的TSS微波（1.43GHz）介电模型。项目还对TSS模型的反演精度进行了检验。TSS模型与来源于NaCl溶液配制的土壤样品的HQR模型比较，研究TSS模型反演氯盐盐渍土含水量和含盐量的精度。项目还利用谐振腔测量野外采集的盐渍土样品的介电常数来比较，分析TSS模型反演苏打盐和硫酸盐盐渍土含水量和含盐量的精度。通过对比分析，HQR模型仅适合于高含盐量和高含水量的氯盐盐渍土盐度的反演，而TSS模型适合于所有类型盐渍土含盐量和含水量的高精度反演。TSS模型还具有自洽性，也即当土壤盐分S趋近于0时，TSS模型还原到Dobson模型。TSS模型介电常数虚部不仅与土壤的含水量和含盐量建立了关系，而且其介电常数实部也与含水量和含盐量建立了紧密的关系，因此，TSS模型具有对称性和普适性。TSS模型的获得，必将为微波遥感业务化定量监测盐渍土盐度，预报盐渍土盐渍化程度和面积奠定了技术基础，为我国干旱半干旱地区经济发展的环境承载力的调查和研究提供关键技术支持。