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首先采用一层非球形粒子植被模型,计算各波段矢量辐射传输方程Mueller矩阵一阶散射解,对比微扰法所得各波段地表粗糙面直接后向散射解,结果证明L波段植被层的散射对观测结果仍有影响,与下垫土壤粗糙表面的散射不易分离。因此,宜采用更低频率的UHF和VHF波段,对地表和次地表层能有较大的渗透深度,并可忽略植被层影响。接着,运用矢量辐射传输的3层土壤全极化Mueller矩阵解,计算UHF/VHF波段分层土壤的散射与传输,分析该两波段探测深度的差异,证实UHF波段可探测大致10—60cm深处的土壤湿度,而VHF波段探测深度能更大一些。根据第3层中土壤体湿度变化0.1时能否引起土壤表面观测的后向散射系数变化0.1dB这一判据,分析VHF波段反演第3层土壤体湿度的必要条件,证实当第2层的体湿度较小时(<0.25)才能反演层3的体温度。基于UHF/VHF两波段探测深度的差异,耗散土壤层的贡献有不同的权重,先后采用UHF和VHF,迭代法实现3层土壤湿度廓线反演。误差分析表明,该方法是有意义的。
First, a non-spherical particle vegetation model is used to calculate the first-order scattering of the Mueller matrix of the radiative transfer equation of each waveband. The direct backscattering solution of the surface rough surface obtained from the perturbation method is compared. The results are still affected, and the underlying surface roughness of the scattering of soil is not easy to separate. Therefore, lower frequencies of UHF and VHF bands should be adopted, which can have greater penetration depth into the subsurface and subsurface layers and neglect the influence of vegetation layers. Then, the scattering and transmission of stratified soil in UHF / VHF band were calculated by using the 3-layer soil fully polarized Mueller matrix solution transmitted by vector radiation. The difference of the detection depth of these two bands was analyzed and it was proved that the UHF band could detect the depth of about 10-60cm Of the soil moisture, while the VHF band exploration depth can be larger. According to the criterion of 0.1 dB change of soil surface observation backscattering coefficient in soil layer 3 in the third layer, the necessary conditions for the inversion of soil layer body humidity in the third layer of VHF band are analyzed. It is confirmed that when the second layer Body temperature of layer 3 can be inverted only when body temperature is small (<0.25). Based on the difference of two depths of UHF / VHF, the contributions of dissipative soil layers have different weights. UHF and VHF are successively used to iteratively measure the three-layer soil moisture profile. Error analysis shows that this method is meaningful.