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土壤介电常数是开展微波土壤水分和冻融状态的监测的基础,也是植被和积雪的下垫面边界条件,然而目前已有的介电常数研究都没有对高有机质含量的土壤开展系统观测。本文将土壤中的自然有机物质分为腐殖质和植物性残留物两类。采用控制变量实验方法,通过测量5种不同有机质含量的东北黑土和加入不同比例毛白杨碎屑的扁都口草甸土,研究了腐殖质和植物性残留物的对土壤介电常数的影响。结果表明,腐殖质会降低干燥土壤的容重,从而发挥间接作用,使介电常数降低;而对于相同容重下观测的潮湿土壤,腐殖质含量较多的土壤介电常数更大。与Dobson模型的比较显示,在29℃室温下,腐殖质对25%重量含水量潮湿土壤实部的影响在±2左右,虚部能达到1。与腐殖质相比,植物性残留物对风干土壤和潮湿土壤的影响都十分明显。植物性残留物能有效地疏松土壤并代入植物组分的介电特征。当重量含水量为30%时,含毛白杨含量为20%的混合土壤比纯扁都口土壤在实部平均减小3—7左右,虚部减小1—3左右。因此,根据实验观测以及和模型的比较,土壤中的有机物质会改变土壤介电性质,对微波遥感造成影响。
The soil dielectric constant is the basis for the monitoring of moisture and freezing-thawing states in microwave soil and the boundary condition of vegetation and snow-covered underlying surface. However, none of the existing dielectric constant studies systematically observed the soil with high organic matter content . In this paper, the natural organic matter in soil is divided into two types of humus and plant residue. The effects of humus and plant residues on soil dielectric constant were studied by using controlled variable experiment method by measuring five kinds of northeast black soil with different organic matter content and flattened meadow soil with different proportions of Populus tomentosa. The results showed that humus could reduce the bulk density of dry soil and thus play an indirect role in reducing the dielectric constant. For the wet soil observed at the same bulk density, the soil with higher humus content had a higher dielectric constant. Comparison with the Dobson model shows that the humus affects the real part of the moist soil at 25% moisture content at ± 2% and the imaginary part at 1% at room temperature of 29 ° C. Compared with humus, plant residues on the air-dried soil and moist soil are very obvious. Phytic residues can effectively loosen soil and substitute the dielectric characteristics of plant components. When the water content was 30%, the mixed soil with 20% Populus tomentosa decreased by about 3-7 on the real part and about 1-3 on the real part. Therefore, based on the experimental observations and comparison with the model, organic matter in the soil will change the soil dielectric properties, affecting microwave remote sensing.