Assessment of the SMAP L3/AP soil moisture product using international ground observation network

Considering the high sensitivity of radiometer signature to soil moisture and the fine spatial resolution of radar system, the objective of this study is to evaluate the performance of soil moisture retrieval using the combination of active and passive microwave remote sensing. To achieve this objective, the quality of the SMAP (Soil Moisture Active Passive mission) L3/AP active-passive soil moisture retrieval product is quantitatively evaluated with respect to ground measurement acquired from the international ground observation networks. The time series of retrieved soil moisture are compared to the ground measurements over two representative test sites located in northern hemisphere and southern hemisphere respectively. The obtained RMSEs are 0.044 m
³
/m
³
and 0.057 m
³
/m
³
for the two sites, which are close to 0.04 m
³
/m
³
and satisfy the original scientific requirement of SMAP mission. However, a slight overestimation around 0.03 m
³
/m
³
is observed on both experimental sites.