基于水云模型的Sentinel-1A双极化反演植被覆盖区土壤水分

Inversion of Soil Moisture in Vegetation-Covered Areas by Sentinel-1A Dual Polarization Based on Water Cloud Model

根据开展的景县地区玉米农田主被动微波遥感协同反演土壤水分监测试验,提出利用FY-3 B WMRI被动微波数据计算微波极化差异指数(MPDI),建立了植被层含水量反演模型,去除植被含水量对于农田土壤水分反演的影响,然后结合植被层含水量反演模型和水云模型,以及Sentinel-1A主动微波数据和部分实测样点土壤体积含水量数据建立植被覆盖区农田土壤水分半经验反演模型,最后验证分析Sentinel-1A VV/VH不同极化条件下土壤水分反演模型的精度。结果表明:VV极化条件下土壤水分反演模型反演精度为R^2=0.7422,RMSE=0.0674 cm^3/cm^3,MAE=0.0305 cm^3/cm^3,MaxE为0.1196 cm^3/cm^3,MinE=0.0024 cm^3/cm^3;VH极化模型为R^2=0.1898,RMSE=0.0768 cm^3/cm^3,MAE=0.0474 cm^3/cm^3,MaxE=0.1933 cm^3/cm^3,MinE=0.0190 cm^3/cm^3。研究区VH极化模型反演值存在普遍偏低现象,VV极化模型土壤水分反演结果优于VH极化模型。VV极化方式具有更强的穿透性,受到植被层衰减作用影响较小,对土壤水分含量变化也更为敏感。建立的VV极化条件下土壤水分反演半经验模型能较好地表征研究区土壤水分空间分布情况。

A collaborative inversion monitoring experiment of active and passive microwave remote sensing for soil moisture in maize farmland in Jingxian County was carried out.Firstly,the microwave polarization difference index(MPDI)was calculated by using FY-3 B WMRI passive microwave data,and the water content of vegetation layer inversion model was established to remove the influence of vegetation water content on farmland soil moisture inversion.Then,a semi-empirical inversion model of farmland soil moisture in vegetation-covered area was established by combining with the vegetation water content inversion model,water cloud model,the Sentinel-1 A active microwave data and some measured soil water content data.Finally,the accuracy of semi-empirical inversion model was verified and analyzed under different sentinel-1 A VV/VH polarization conditions.The results show that the accuraces of soil moisture inversion values under VV polarization condition can be characterized by R2(0.7422),RMSE(0.0674)cm3/cm3,MAE(0.0305 cm3/cm3),Max R2,(0.1196 cm3/cm3),MinE(0.0024 cm3/cm3);R2(0.1898),RMSE(0.0768 cm3/cm3),MAE(0.0474 cm3/cm3),MaxE(0.1933 cm3/cm3),MinE(0.0190 cm3/cm3)under VH polarization condition.The inversion values of the VH polarization model in the study area were generally low,and the soil moisture inversion results of the VV polarization model were better than that of the VH polarization model.The VV polarization mode has stronger penetrability which is less affected by the attenuation of the vegetation layer,and is more sensitive to the changes in soil moisture content.The semi-empirical model of soil moisture inversion under VV polarization condition can better reflect the spatial distribution of soil moisture in the study area.