Update and Make Operational SMOPS with Observations from GCOM-W/AMSR2 and Near-real-time SMOS
Principal Investigator: Xiwu Zhan
NRT SMOS soil moisture retrieved from SMOPS NRT SMOS TB data
ESA SMOS Level 2 soil moisture product
NRT SMOS soil moisture products are comparable with the ESA SMOS Level 2 soil moisture product. SMOPS NRT SMOS soil moisture data has a latency less than 6 hours while the official ESA SMOS soil moisture products are mostly 12 hours late.
The Soil Moisture Operational Products System (SMOPS) is NESDIS' operational global system for providing reliable soil moisture data to the experimental and operational numerical weather prediction models of the National Weather Service (NWS) National Centers for Environmental Prediction (NCEP). SMOPS currently uses data from the Advanced Scatterometer (ASCAT) on MetOp-A and B of the European Organisation for the Exploitation of Meteorological Satellite Data (EUMETSAT), Soil Moisture Ocean Salinity (SMOS) of the European Space Agency (ESA), and WindSat of the Department of Defense (DoD) Naval Research Laboratory (NRL). The SMOS soil moisture data feed has roughly 12-hour latency, but SMOS Level-1 brightness temperature data latency is less than 3 hours. Since 12-hour latency is too long for use in operational numerical weather models, one of the FY15 tasks of the SMOPS project was to use the SMOPS retrieval algorithm to retrieve soil moisture with latency significantly shorter (about 5 hours) than the official SMOS soil moisture product latency.
To obtain an observation of brightness temperature, ESA uses a complicated antenna model with heavy computational costs, which is the main reason why the SMOS official soil moisture product latency is so long. To speed up the retrieval process, we developed a quadratic regression equation to fit the distribution of the brightness temperature as a function of incidence angle in order to obtain fixed- angle near real time (NRT) TBs. This simplified approach produced NRT TB fields similar to ESA SMOS official SMOS L2 TB products in a fraction of the time.
To retrieve soil moisture, surface temperature (Ts) is also required in addition to the optical depth (Τ) of the vegetation cover. SMOPS ingests Ts data from the NCEP Global Forecast System (GFS) and interpolates them to each grid for the time when the TB data are acquired from SMOS. The value of Τ is estimated from Enhanced Vegetation Index (ESI) which is in turn obtained from the Suomi National Polar- orbiting Partnership (S-NPP) Visible Infrared Imaging Radiometer Suite (VIIRS). Using the Single Channel Algorithm (SCA), SMOPS could retrieve soil moisture for an orbit file within two hours after it arrives. The final SMOS soil moisture products obtained from our NRT TB data are also similar to the ESA SMOS official Level 2 soil moisture data products with significantly shorter latency (figures at right). In addition, SMOPS has been updated with data from the Japanese Aerospace Exploration Agency (JAXA)'s Global Change Observation Mission (GCOM)-Water 1 (W1) Advanced Microwave Scanning Radiometer-2 (AMSR2). The Level 2 soil moisture retrievals in swath files are obtained from NESDIS GAAPS which is developed by NESDIS GCOM-W1/AMSR2 project team. The additional sensor improves spatial coverage of the available soil moisture fields, especially for the 6-hour images.