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An important component of satellite-based soil moisture algorithm development and validation is the comparison of coincident remote sensing and in situ observations that are typically provided by intensive field campaigns. The planned NASA Soil Moisture Active Passive (SMAP) mission has unique requirements compared to previous soil moisture satellite programs because both active and passive microwave observations are needed. The primary source of these combined observations has been an aircraft-based SMAP simulator called PALS (Passive and Active L-band System). This paper presents an overview of the field experiment data collected using PALS that spans 10 years. Data from the various campaigns were merged to form a single data set. Analyses showed that the data set contains an extensive range of soil moisture values collected under a variety of conditions and that the quality of both the PALS and ground truth data meets the needs of SMAP algorithm development and validation. The study suggests that the data set should be expanded in order to achieve globally representative land cover diversity and that more observations under dense vegetation conditions and longer time series would be desirable.
