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林下枯枝落叶层会衰减来自土壤的微波辐射信号,降低微波辐射亮温对地表参数变化的敏感性,从而影响林下地表参数的反演精度。为了定量研究枯枝落叶层的衰减特性,基于τ-ω模型,通过严格的理论推导证明了利用不同厚度下的枯枝落叶层亮温计算衰减系数的可行性,并基于该理论方法设计可控实验,获取了双频段(18.7GHz和36.5GHz)上不同厚度、不同重量含水量的枯枝落叶层亮温值,然后定量分析了枯枝落叶层的衰减系数随重量含水量的变化过程,同时根据计算的消光系数,分析了不同厚度、不同重量含水量下的枯枝落叶层透过率。结果表明:较干燥的枯枝落叶层的衰减系数较小,透过率较高,但是随着含水量增大,衰减系数会出现急剧的增加,从而造成透过率骤减;高频波段的衰减系数变化更加迅速,由枯枝落叶层引起的衰减作用更加明显;单次散射反照率ω随重量含水量的变化趋势为先升高后降低。该研究有利于理解森林系统中微波辐射传输过程,纠正森林区微波辐射亮温,提高森林下地表参数遥感反演精度。
The litter layer under the forest will attenuate the microwave radiation signal from the soil and reduce the sensitivity of the microwave radiation temperature to the variation of the surface parameters, thus affecting the inversion accuracy of the surface parameter under the forest. In order to quantitatively study the decay characteristics of litter layer, based on the τ-ω model, the feasibility of calculating the attenuation coefficient using the light temperature of litter layer under different thicknesses is proved through strict theoretical derivation. Based on the theoretical method, the design of controllable Experiments were conducted to obtain the brightness temperature of litter layer with different thicknesses and different weights in the two bands (18.7GHz and 36.5GHz), and then the decay coefficient of the litter layer with the change of weight and water content was quantitatively analyzed. Meanwhile, Based on the calculated extinction coefficient, the permeability of litter layer under different thicknesses and moisture contents was analyzed. The results showed that the dry litter layer had a small attenuation coefficient and a high transmittance, but its attenuation coefficient increased sharply with the increase of water content, resulting in a sharp decrease of transmittance. In the high frequency band The attenuation coefficient changes more rapidly and the decay effect caused by the litter layer is more obvious. The change tendency of the single scattering albedo ω with weight water content firstly increases and then decreases. The study is helpful to understand the microwave radiation transmission in forest system, correct the bright temperature of microwave radiation in forest area, and improve the accuracy of remote sensing inversion of surface parameters under forest.