在基于TDR、FD和SWR等不同方法的土壤水分测量仪器中多针土壤探头作为采样传感器的一个重要组成部分，深入研究它的阻抗计算方法对于改进这些仪器的测量精确度具有很高的理论与应用价值。由于描述多针土壤探头电磁特性的麦克斯韦尔方程的边界条件很难确定，所以试图利用麦氏方程的解析解分析其阻抗特性从理论上说是“可望而不可及”的。本文依据高频传输线阻抗变换理论与数学分析中夹逼定理的思想提出了一种土壤探针阻抗计算模型。进一步通过对该模型的计算机仿真与实验研究，发现土壤探针的阻抗特性可随着测试频率与针长等相关参数的改变在感性负载与容性负载间相互转化。此外，当这些相关参数改变时，土壤探针的阻抗计算模型还存在着周期性的间断点。

A polarized He-Ne laser light was used in a laboratory environment to measure soil moisture content. Depolarization of the light beam was used as an indicator of dielectric constant, which, in turn, indicated soil moisture content. Fourier analysis was used to analyze the signals. The DC component and the second harmonic of the Fourier spectrum were used to calculate the degree of depolarization. This method greatly reduced the effects of noise from various sources on the measurement of degree of depolarization. Three soil types (silt-loam, loam, and loam-sand) were tested. For all three soil types, degree of depolarization decreased with an increase of moisture content. The change was most significant for loam, followed by silt loam and loam sand.

基于电流-电压四端法的“polar-djpole array”形式，以壤土作为研究对象，对土壤含水率和土壤盐分与土壤电导率之间的相互关系进行了试验研究。结果表明，在土壤盐分和含水率2个相关因素中，土壤盐分对土壤电导率的影响较土壤含水率要大得多。

Determination of soil water content in situ is complicated due to variations in dielectric constant of porous media. Time domain reflectometry (TDR) may meet the need for measurement of soil moisture with high accuracy. However, TDR-type instruments are expensive. A theory, which is called standing-wave ratio (SWR) of transmission line, is proposed in this paper. This theory has been proven a valuable tool for measuring soil water content. A method for calculating the characteristic impedance of a four-wire probe was developed. Furthermore, a prototype of a SWR-type sensor equipped with a new soil probe was designed.The measurement error was found to be within

土壤介电常数是影响土壤含水率快速、准确和可靠测量的关键参数。通过检测土壤介电常数换算出土壤含水率的测量方法已成功地应用在基于TDR原理的现代先进测量仪器中。文中依据传输线理论探讨了基于驻波比原理的土壤介电常数测量方法，解决多针探头特征阻抗的计算，实验结果证实了理论分析的正确。