含水含盐土壤的微波介电特性分析研究

用微波网络分析仪测量了实验室制备的各种不同含水量,含盐量的土壤样品的复介电常数,研究了介电常数的实部和虚部与频率、盐度、含水量的关系。研究表明:频率、盐度对土壤介电常数实部的影响很小;对于某一特定土壤,其介电常数的实部由土壤的含水量决定;在较低频率范围内（f<2GHz）,虚部随着频率的增大而迅速下降,高频部分则趋向于一定值,波长较长的波段,如P波段或L波段对土壤含盐程度具有更高的敏感性,含盐量对虚部在较低频范围（f<5GHz）影响很大。同时,采集了内蒙古吉兰泰盐湖区的土壤样品,并测量了其复介电常数,与同步过顶的RADARSAT图像进行了相关分析。分析结果表明雷达图像记录的后向散射强度与含盐土壤复介电常数实部的相关系数为0.23,与虚部的相关系数为0.66,即雷达图像观测的含盐含水士壤的后向散射强度与土壤的含盐量相关性较高。这为利用微波遥感进行土壤盐碱化程度监测,提供了可能和实验依据。

Study on Soil Microwave Dielectric Characteristic as Salinity and Water Content

This paper presents the experimental measurements of the complex dielectric constants in two groups of soil samples using the microwave network analyzer. One group is the laboratory prepared soil samples with different moisture and salinity contents. We evaluated real parts and imaginary parts of dielectric constants as a function of microwave frequency , salinity, and water content. The real part is strongly affected by the soil moisture, whereas the frequency and the salinity of soils have little influence on it. The imaginary part is strongly affected by salinity at low frequencies(f< 5GHz) .When f< 2GHz the imaginary part decreases with the increment of frequency; whereas, at higher frequencies it tends toward a constant. The longer wavelength band, such as L-band, has better sensitivity to soil salinity than shorter wavelength. Another group of soil samples were cllected in the Jilantai Salt Lake area. The measurements are well agreed with the group one. Then we analyze the simultaneous pass RADARSAT image at the Jilantai Salt Lake area. The correlation coefficient between the backscattering intensity values of the RADARSAT image and the real parts of the salt soil is 0.23 , whereas the correlation coefficient for the imaginary part is 0.66. That indicates the backscattering coefficient of the radar image well correlated with the salinity of salt-affected soil.This study provides an experimental basis for future soil salinity monitoring using microwave remote sensing.