SMAP Level 4 Soil Moisture (L4_SM)
The objective of the SMAP Level 4 Soil Moisture (L4_SM) product is to provide estimates of surface and root zone soil moisture that are informed by and consistent with SMAP observations. Such estimates are obtained by merging SMAP observations with estimates from a land surface model in a soil moisture data assimilation system.
Version 2 of the L4_SM product was released on April 29, 2016 and provides validated data products.
On May 8, 2016, a major rain event in the interior of Australia was observed by the Bureau of Meteorology (A) but poorly represented in the global input data for the L4_SM system (B). The precipitation observations rely on high-quality, local gauge measurements from the Bureau of Meteorology. The precipitation used in the L4_SM system is based on the daily, global, 0.5° gauge product from the NOAA Climate Prediction Center (CPC).
Due to the lack of rainfall in the L4_SM system, the soil moisture in the model forecast for 21:00 UTC was too dry, and therefore the modeled L-band brightness temperature (Tb) was too high compared to SMAP observations (C).
The L4_SM analysis of SMAP Tb observations thus resulted in a substantial correction of the model forecast soil moisture (D) and, consequently, an improvement in the L4_SM data product.
The L4_SM algorithm is a variant of the NASA GEOS-5 land data assimilation system and includes the following components:
- Distributed ensemble Kalman filter (EnKF)
- NASA GEOS-5 Catchment land surface model
- Surface meteorological forcing from NASA GEOS-5 Forward Processing system
- Precipitation corrections with NOAA Climate Prediction Center &dquot;Unified&dquot; global, 0.5 degree gauge-based product
- SMAP L1C_TB observations
- Seasonal Tb bias correction
References
De Lannoy, G. J. M., and R. H. Reichle (2015), Global Assimilation of Multi-Angular SMOS Brightness Temperature Observations into the GEOS-5 Catchment Land Surface Model for Soil Moisture Estimation, Journal of Hydrometeorology, 17, 669-691, doi:10.1175/JHM-D-15-0037.1.
Entekhabi, D. et al. (2014), SMAP Handbook–Soil Moisture Active Passive: Mapping Soil Moisture and Freeze/Thaw from Space. Pasadena, CA USA: SMAP Project, JPL CL#14-2285, Jet Propulsion Laboratory.
Reichle, R. H., and Q. Liu (2014), Observation-Corrected Precipitation Estimates in GEOS-5. NASA/TM2014-104606, Vol. 35. Global Modeling and Assimilation Office, Goddard Space Flight Center, Greenbelt, MD. Available from http://gmao.gsfc.nasa.gov/pubs/tm/
Reichle, R. H., R. Koster, G. De Lannoy, W. Crow and J. Kimball (2014), SMAP Algorithm Theoretical Basis Document: L4 Surface and Root-Zone Soil Moisture Product. SMAP Project, JPL D-66483, Jet Propulsion Laboratory, Pasadena, CA. http://nsidc.org/sites/nsidc.org/files/files/272_L4_SM_RevA_web.pdf, 1.4 MB
Reichle, R. H., R. A. Lucchesi, J. V. Ardizzone, G.-K. Kim, E. B. Smith, and B. H. Weiss (2015), Soil Moisture Active Passive (SMAP) Mission Level 4 Surface and Root Zone Soil Moisture (L4_SM) Product Specification Document. GMAO Office Note No. 10 (Version 1.4), 82 pp, NASA Goddard Space Flight Center, Greenbelt, MD, USA. Available from http://gmao.gsfc.nasa.gov/pubs/office_notes/
Reichle, R. H. et al. (2015), Soil Moisture Active Passive (SMAP) Project Assessment Report for the Beta-Release L4_SM Data Product. NASA/TM2015-104606, Vol. 40. Global Modeling and Assimilation Office, Goddard Space Flight Center, Greenbelt, MD. Available from http://gmao.gsfc.nasa.gov/pubs/tm/
Reichle, R. H., et al. (2016), Soil Moisture Active Passive Mission L4_SM Data Product Assessment (Version 2 Validated Release), NASA GMAO Office Note, No. 12 (Version 1.0), 55pp, National Aeronautics and Space Administration, Goddard Space Flight Center, Greenbelt, Maryland, USA. Available from http://gmao.gsfc.nasa.gov/pubs/office_notes/
Reichle, R., G. De Lannoy, R. Koster, W. Crow, and J. Kimball (2016), SMAP L4 9 km EASE-Grid Surface and Root Zone Soil Moisture Analysis Update. Version 2. Boulder, Colorado USA: NASA National Snow and Ice Data Center Distributed Active Archive Center. DOI:10.5067/JJY2V0GJNFRZ.
Reichle, R., G. De Lannoy, R. Koster, W. Crow, and J. Kimball (2016), SMAP L4 9 km EASE-Grid Surface and Root Zone Soil Moisture Geophysical Data. Version 2. Boulder, Colorado USA: NASA National Snow and Ice Data Center Distributed Active Archive Center. DOI:10.5067/YK70EPDHNF0L.
Reichle, R., G. De Lannoy, R. Koster, W. Crow, and J. Kimball (2016), SMAP L4 9 km EASE-Grid Surface and Root Zone Soil Moisture Land Model Constants. Version 2. Boulder, Colorado USA: NASA National Snow and Ice Data Center Distributed Active Archive Center. DOI:10.5067/VBRUC1AFRQ22.
