The SMAP Level-1, -2, -3, and -4 data sets from the NASA National Snow and Ice Data Center Distributed Active Archive Center (NSIDC DAAC) will be updated in summer 2020 as part of a scheduled annual reprocessing campaign. Several improvements will be implemented to these data sets, both standard and enhanced, and include the following highlights:
- Improved calibration methodology will be applied to the SMAP Level-1 radiometer brightness temperatures based on the internal instrument noise diode, deep-space measurements during monthly Cold Sky Maneuvers, stable open-ocean targets, and antenna system signal losses. The Level-2, -3 and -4 algorithms will be updated to use the new Level-1 observations.
- Soil temperatures from the NASA Global Modeling and Assimilation Office (GMAO) will be used to estimate the soil microwave emission temperature needed to produce the SMAP Level-2 and -3 soil moisture estimates. GMAO transitioned to using an improved land surface model in early 2020, which required adjustments of the procedure used to estimate soil microwave emission temperatures from the GMAO soil temperature data.
- Data quality flags will be updated and corrected where faulty.
- Improvements will be applied to the Dual Channel Algorithm (DCA). This algorithm, which was first introduced last year as the Modified “DCA” (MDCA) in the Level-2 data sets as “option 3” algorithm, produces simultaneous estimates of soil moisture and vegetation optical depth.
- Improved estimates of soil clay fraction and bulk density will be used to produce Level-2 and -3 soil moisture estimates. The new soil texture database avoids artifacts of political boundaries and watershed/geologic delineations that existed in the older composite data set.
As is done for each version update, each data set will be accompanied by Assessment Reports that provide performance metrics for the improved algorithms over a longer time period (2015-2020) than used in computing previous performance metrics.
Access to SMAP data sets and related documentation can be found at https://nsidc.org/data/smap/smap-data.html.