ETL Airborne Sensor Enables Global Soil Moisture Observations

Contact: Al Gasiewski

Soil moisture has a significant impact on human safety and our economy. It affects land-use and agricultural planning and the cost, quantity, and quality of food. Accurate weather forecasts require the rate of transfer of soil moisture to the atmosphere, whether by evaporation or plant transpiration. Trends in soil moisture are also reflected in climate and regional weather, and affect drought and fire danger levels. Detecting excessive soil moisture is needed for flood warning and mitigation.

To extend sparse observations of soil moisture at ground stations to national and global coverage requires microwave radiometers aboard satellites. A new instrument to be used by NOAA for weather and climate forecasting applications is the Japanese Advanced Microwave Scanning Radiometer E (AMSR-E), recently launched on the NASA Aqua satellite. AMSR-E images the Earth's microwave radiation in C- and X-bands, both of which are sensitive to soil moisture and vegetation cover, but with differing sensitivities that permit separation of soil moisture and vegetation information.

Optimal use of AMSR-E data by NOAA and other agencies requires an understanding of how to use the C- and X-band data for all types of soil and vegetation conditions. Accordingly, NOAA/ETL is working with the USDA and NASA during the Soil Moisture Experiments in 2003 (SMEX03) campaign and to make critical airborne measurements needed to interpret AMSR-E data. SMEX03 was designed to provide data to further develop and validate algorithms to accurately retrieve soil moisture from current satellite radiometers such as AMSR-E as well as future microwave sensors such as the NPOESS Conical Microwave Imager and Sounder (CMIS). SMEX03 includes several study regions (Oklahoma, Alabama, Georgia, and Brazil) to provide a diversity of soil types, moisture levels, and vegetation cover.

SMEX03 uses as its principal airborne instrument the ETL Polarimetric Scanning Radiometer (PSR) system with C- and X-bands (PSR/CX). PSR/CX provides unique conically-scanned airborne microwave imagery with full polarization capability and high spatial resolution. The system also detects and rejects the anthropogenic radio interference that has been shown to corrupt many AMSR-E measurements. The small pixel size of PSR/CX (~0.5 km compared with ~75 km for AMSR-E) provides an important bridge across the large range of sampling scales from that of the SMEX03 ground stations to the AMSR-E satellite imagery.

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