Abstract
Sensitivity analysis is critically needed to better understand the microwave emission model for soil moisture retrieval using passive microwave remote sensing data. The vegetation b-factor along with vegetation water content and surface characteristics has significant impact in model prediction. This study evaluates the sensitivity of the b-factor, which is function of vegetation type. The analysis is carried out using Passive and Active L and S-band airborne sensor (PALS) and measured field soil moisture from Southern Great Plains experiment (SGP99). The results show that the relative sensitivity of the b-factor is 86% in wet soil condition and 88% in high vegetated condition compared to the sensitivity of the soil moisture. Apparently, the b-factor is found to be more sensitive than the vegetation water content, surface roughness and surface temperature; therefore, the effect of the b-factor is fairly large to the microwave emission in certain conditions. Understanding the dependence of the b-factor on the soil and vegetation is important in studying the soil moisture retrieval algorithm, which can lead to potential improvements in model development for the Soil Moisture Active-Passive (SMAP) mission.
Highlights
Soil moisture is a very important variable in hydrology because its variations influence the evolution of weather and climate
Understanding the dependence of the b-factor on the soil and vegetation is important in studying the soil moisture retrieval algorithm, which can lead to potential improvements in model development for the Soil Moisture Active-Passive (SMAP) mission
Considering the effect of the b-factor to the soil moisture retrieval, which is the main factor of the optical depth along with the vegetation water content, the sensitivity analysis for the microwave emission model is carried out
Summary
Soil moisture is a very important variable in hydrology because its variations influence the evolution of weather and climate. Microwave remote sensing in low frequency has been optimal to estimate soil moisture since it is very sensitive to the dielectric properties of the soil [4,5]. Because of relatively longer penetration in low frequencies, the L-band has been assumed to have lower sensitivity to the vegetation so far, and is relatively transparent [3,4,8]. Further investigation of the b-factor depends on vegetation types in low frequencies are studied here by analyzing previously published data and evaluating with SGP99 experiment. The relative sensitivity of the b-factor is carried out through a comparison with soil moisture, vegetation water content, soil roughness and surface temperature in different soil and vegetation condition. The relationship between the b-factor and different vegetation types is analyzed using field soil moisture and vegetation water content data from SGP99
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