L波段对不同盐类土壤的微波介电特性分析

 土壤盐碱化是世界面临的一大难题。微波遥感探测土壤具有优势,L波段对土壤含水量和含盐量较为敏感。为了分析不同盐类对土壤介电特性的影响,本文利用L波段(1.43 GHz)微波谐振腔测量了我国盐碱土中普遍存在的3种盐类(NaCl,Na₂SO₄,NaHCO₃)土壤样品的介电常数,研究了土壤介电常数与含水量、含盐量和盐种类的关系。得出结论:实部主要由土壤的含水量决定,含盐量对实部的影响无明显规律;虚部值随含水量和含盐量的增加而增大;3种盐类土壤介电常数虚部随含盐量变化呈现不同的递增趋势,在含盐浓度一定的条件下,虚部值是ε″ _NaCI>ε″ _NaHCO3>ε″ _Na2SO4;在某一含盐量点3种盐类土壤虚部随含水量变化的斜率不同,以此能将3种盐类区分。该研究为建立含不同盐类土壤介电常数模型和微波遥感监测土壤盐碱化提供了实验的依据。

Study on Microwave Dielectric Properties of Different Salt Soils at L-Band

Soil salinity caused by natural or human-induced processes is a severe environmental hazard all over the world.Approximately 955 M ha of soil have been affected by primary salinization worldwide,whereas secondary salinization affects approximately 77 M ha,with 58% of these in irrigated areas.This requires careful monitoring of soil salinity and mapping of the extent of salinized soils.Microwave remote sensing can significantly contribute to the detection of changes in salt-affected surface features.This paper describes a L-band resonant cavity technique at 1.43 GHz used to measure the complex dielectric constants of salt soils which contain NaCl,Na2SO4 and NaHCO3 respectively.The purpose of the new measurements is to evaluate the real components and imaginary components of dielectric constants as a function of water content,salinity and types of salts.The measurements on the dielectric properties of different salt soils show that the real components are strongly affected by soil moisture,for they increase with the increment of water content,whereas salinity has little influence on them,they tend toward constants.The imaginary components are not only dependent on water content and salinity but also on types of salts.Besides increasing with water content,the imaginary components of the three salt soils show different increasing trends with the increment of salt content.The value of imaginary component is ε″ NaCIε″ NaHCO3ε″ Na2SO4 under the condition of same saline concentration.Moreover,the slopes of the three salt soils vary with the change of water content that can distinguish the three salt soils.This study proves that L-band has a good sensitivity to soil salinity,and provides an experimental basis for the salt soil dielectric constant model building and future soil salinity monitoring using microwave remote sensing.