Dynamic b_p in the L Band and Its Role in Improving the Accuracy of Soil Moisture Retrieval

【摘要】 The parameter b_p in the tuo-omega(τ–ω)model is important for retrieving soil moisture data from passive microwave brightness temperatures.Theoretically,b_p depends on the observation mode(polarization,frequency,and incidence angle)and vegetation properties and varies with vegetation growth.For simplicity,previous studies have taken b_p to be a constant.However,to reduce the uncertainty of soil moisture retrieval further,the present study is of the dynamics of b_p based on the SMAPVEX12 experimental dataset by combining a genetic algorithm and the L-MEB microwave radiative transfer model of vegetated soil.The results show the following.First,b_p decreases nonlinearly with vegetation water content(VWC),decreasing critically when VWC becomes less than 2 kg/m~2.Second,there is a power law between b_p and VWC for both horizontal and vertical polarizations(R~2=0.919 and 0.872,respectively).Third,the effectiveness of this relationship is verified by comparing its soil-moisture inversion accuracy with the previous constant-b_p method based on the HiWATER dataset.Doing so reveals that the dynamic b_p method reduces the root-mean-square error of the retrieved soil moisture by approximately 0.06 cm~3/cm~3,and similar improvement is obtained for the calibrated SMAPVEX12 dataset.Our results indicate that the dynamic b_p method is reasonable for different vegetation growth stages and could improve the accuracy of soil moisture retrieval.更多还原

【Abstract】 The parameter b_p in the tuo-omega(τ–ω)model is important for retrieving soil moisture data from passive microwave brightness temperatures.Theoretically,b_p depends on the observation mode(polarization,frequency,and incidence angle)and vegetation properties and varies with vegetation growth.For simplicity,previous studies have taken b_p to be a constant.However,to reduce the uncertainty of soil moisture retrieval further,the present study is of the dynamics of b_p based on the SMAPVEX12 experimental dataset by combining a genetic algorithm and the L-MEB microwave radiative transfer model of vegetated soil.The results show the following.First,b_p decreases nonlinearly with vegetation water content(VWC),decreasing critically when VWC becomes less than 2 kg/m~2.Second,there is a power law between b_p and VWC for both horizontal and vertical polarizations(R~2=0.919 and 0.872,respectively).Third,the effectiveness of this relationship is verified by comparing its soil-moisture inversion accuracy with the previous constant-b_p method based on the HiWATER dataset.Doing so reveals that the dynamic b_p method reduces the root-mean-square error of the retrieved soil moisture by approximately 0.06 cm~3/cm~3,and similar improvement is obtained for the calibrated SMAPVEX12 dataset.Our results indicate that the dynamic b_p method is reasonable for different vegetation growth stages and could improve the accuracy of soil moisture retrieval.更多还原