A Long-Term Consistent Multi-Satellite Soil Moisture ESDR with Uncertainty Information

Principal Investigator (PI): Steven Chan, NASA's Jet Propulsion Laboratory

As a surface hydrosphere state variable, soil moisture plays a key role in global terrestrial hydrology. It controls the partitioning of water and energy fluxes at the land surface. This partitioning affects not only the relative propensity between infiltration and surface runoff during precipitation, but also the energy exchange between the land and atmosphere systems. This energy exchange has been shown in recent studies to have a strong impact on the feedbacks between land and atmosphere that lead to climate anomalies.

Because of their unique vantage in space, satellites remain the only practical means for obtaining soil moisture observations at sufficient resolution, frequency, and coverage. We propose to develop such a ESDR using two composite sets of multi-satellite cross-calibrated brightness temperature observations:

• X-band (10.7 GHz) brightness temperatures cross-calibrated among:
  • GPM Microwave Imager (GMI),
  • Advanced Microwave Scanning Radiometer-2 (AMSR2),
  • WindSat, Advanced Microwave Scanning Radiometer-EOS (AMSR-E), and
  • the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) from the Global Precipitation Measurement (GPM) Level 1C Common Calibrated Brightness Temperatures (GPMXCAL), and
• L-band (1.4 GHz) brightness temperatures cross-calibrated between:
  • Soil Moisture Active Passive (SMAP) and
  • Soil Moisture and Ocean Salinity (SMOS)

When considered together, the combined passive microwave observations cover a period of more than two decades (1997–present), providing the basis for producing a long-term consistent multi-satellite soil moisture ESDR, with soil moisture estimates from different contributing soil depths available during the overlap period of the X- and L-band satellites considered above.

Soil moisture estimates will be derived from brightness temperatures at both frequencies using established algorithms, validated physical models, and robust ancillary data leveraged from the team’s direct involvement in the development of previous and current official NASA-sponsored single-satellite soil moisture data products including AMSR-E (2002–2011, Njoku, 2004), Aquarius (2011–2015, Bindlish and Jackson, 2015), SMAP (2015–present, O'Neill et al., 2016), near real-time AMSR2 (2016–present, Njoku and Jackson, 2016), and multi-satellite soil moisture data product (AMSR-E/AMSR2 Unified [2002–present, Jackson et al., 2016]).

Stochastic sensitivity analysis will be performed to determine the uncertainty associated with each estimate on a pixel-by-pixel basis (Crow et al., 2005). Established performance metrics such as unbiased RMSE, RMSE, bias, and correlation of the final ESDR will be further assessed against multi-year in situ soil moisture ground measurements collected at USDA watershed sites across the U.S. as well as other archived datasets. The proposed ESDR has a tentative retrieval accuracy target of unbiased RMSE (aka anomaly RMSE) of 0.06 m³/m³ or less for the X-band product and 0.04 m³/m³ or less for L-band over non-frozen land surfaces that are free of excessive snow, ice, mountainous terrain, and dense vegetation coverage.

Publications:

• Bindlish, R. and Jackson, T. (2015). Aquarius L2 Swath Single Orbit Soil Moisture, Version 4. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center (NSIDC DAAC). doi:10.5067/Aquarius/AQ2_SM.004
• Crow, W. T. et al., (2005). “An observing system simulation experiment for Hydros radiometeronly soil moisture products,” in IEEE Transactions on Geoscience and Remote Sensing, vol. 43, no. 6, pp. 1289-1303. doi:10.1109/TGRS.2005.845645
• Jackson, T. J., Chan, S., Bindlish, R., and Njoku, E. G. (2016). AMSR-E/AMSR2 Unified L2B Half- Orbit 25 km EASE-Grid Surface Soil Moisture, Version 1. Boulder, Colorado USA. NASA NSIDC DAAC doi:10.5067/IKQ0G7ODMLC7
• Njoku, E. G. (2004). AMSR-E/Aqua L2B Surface Soil Moisture, Ancillary Parms, & QC EASEGrids. Version 2. Boulder, Colorado USA: NASA NSIDC DAAC doi:10.5067/AMSR-E/AE_LAND.002
• Njoku, E. and Jackson, T. (2016). NRT AMSR2 Unified L2B Half-Orbit 25 km EASE-Grid Surface Soil Moisture. Dataset available online from NASA LANCE AMSR2 at GHRC DAAC. doi:10.5067/AMSR2/A2_Land_NRT
• O'Neill, P. E., Chan, S., Njoku, E. G., Jackson, T., and Bindlish, R. (2016). SMAP L2 Radiometer Half-Orbit 36 km EASE-Grid Soil Moisture, Version 4. Boulder, Colorado USA. NASA NSIDC DAAC doi:10.5067/XPJTJT812XFY.