关键词: 土壤盐度, 介电常数, 盐种类, 微波谐振腔

Abstract:

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″ _NaCI>ε″ _NaHCO3>ε″ _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.

Key words: dielectric constant, microwave resonant cavity, soil salinity, types of salts