冬小麦覆被农田地表多层非均质混合电磁散射模型研究

Electromagnetic Scattering Model of Farmland Surface Covered with Winter Wheat

冬小麦种植区域分布广泛,为监测与评估其生长信息和生长环境,本文通过引入三相混合介质模型表征植被层,引入高斯随机粗糙面表征农田粗糙地表,构建了一种冬小麦覆被农田地表的多层非均质混合电磁散射模型。首先分别对比本文提出的多层非均质混合模型与水云模型、Oh模型在冬小麦拔节期及孕穗期的后向散射系数预测结果,对本模型的有效性进行分析和验证;随后,通过分析该模型等效介电常数,并求解其电磁散射及辐射传输方程,获取植被生长信息、植被含水率及土壤粗糙度等因素对覆被农田地表等效介电常数和雷达后向散射系数的影响规律。结果表明,本文提出的多层非均质混合模型与水云模型及Oh模型预测结果有较好的一致性,同时与双弥散模型获得的小麦层等效介电常数R2分别为0.9817、0.9922、0.9863、0.9711,同样具有较好的一致性;此外,本文提出的模型对拔节期、孕穗期小麦含水率的预测结果与实际测量值的均方根误差分别为0.88%、4.65%,该模型能够较好地模拟覆被农田地表电磁散射特征,为后续无人机微波反演冬小麦生长及土壤水分信息提供坚实理论基础。

In order to monitor and evaluate the growth information and environment of winter wheat,a multilayer non⁃homogeneous hybrid electromagnetic scattering model was constructed for winter wheat overlaying farmland surface by introducing a three⁃phase mixed⁃media model to characterize the vegetation layer and a Gaussian random roughness surface to characterize the rough surface of the farmland.Firstly,the validity of the model was analyzed and verified by comparing the backward scattering coefficient prediction results of the proposed multilayer non⁃homogeneous hybrid model with those of the water cloud model and the Oh model in the nodulation and tasseling stages of winter wheat.Subsequently,the model equivalent dielectric constant was analyzed and the electromagnetic scattering and radiative transfer equations were solved to obtain the effects of the vegetation growth information,the water content of vegetation and the soil roughness on the surface of the covered farmland.The effect of factors such as vegetation growth information,vegetation water content and soil roughness on the surface equivalent dielectric constant and radar backscattering coefficient of the covered farmland was obtained.The results showed that the multilayer non⁃homogeneous hybrid model proposed was in good agreement with the prediction results of the water cloud model and the Oh model,and in good agreement with the equivalent dielectric constant R2 of the wheat layer obtained by the double dispersion model with the values of 0.9817,0.9922,0.9863,0.9711,respectively.Moreover,the R2 of the model proposed for the prediction results of the water content of the wheat at the stage of pulling out and the stage of spiking were the same as the actual measurement values,and the R2 of the predicted results were the same as the predicted results of the model.The RSME of the prediction results and the actual measured values were 0.88%and 4.65%,respectively,and the model can better simulate the electromagnetic scattering characteristics of the surface of the overlying farmland,which provided a solid theoretical basis for the subsequent UAV microwave inversion of winter wheat growth and soil moisture information.