Soil Moisture Mapping During SMEX03 Using Airborne NOAA C- and X-band Polarimetric Scaning Radiometer (PSR)

Remote sensing of soil moisture can be accomplished using L-band (~1.4 GHz) microwave radiometry, and such data provides reasonable penetration of crop vegetation canopy as well as measurements of soil moisture at soil depths of up to ~10 cm. Radiometry using higher microwave frequencies provides progressively less penetration of vegetation and soil probing depth, but is more amenable to implementation using airborne or spaceborne antennas of practical size. The Japanese AMSR-E imaging radiometer on board the NASA EOS Aqua satellite is one such sensor capable of retrieving soil moisture using a microwave channel at 6.9 GHz with ~75 km spatial resolution. Aqua was launched in May 2002, and will provide a global soil moisture product based on AMSR-E data The Soil Moisture Experiments in 2002 and 2003 (SMEX02/03) campaign were designed to provide early post-launch validation for Aqua via an airborne imaging study that simulates AMSR-E low-frequency microwave imagery. The airborne sensor used for the simulation is the NOAA Polarimetric Scanning Radiometer (PSR) operated on the NASA Wallops Flight Facility's P-3B aircraft. The PSR is the only operational airborne radiometer system to provide multiband polarimetric brightness imagery. It was developed at the Georgia Institute of Technology and the NOAA Environmental Technology Laboratory starting in 1995 in response to a general national need for high-resolution multiband polarimetric imagery for satellite algorithm development and calibration/validation studies. Objectives of the PSR flights during SMEX03 included: (1) providing high-resolution AMSR-E (55° incidence) underflight data at vertical and horizontal polarization, (2) developing algorithms using combined C- and X-band data for soil moisture retrieval in the presence of several types of vegetation canopies, (3) studying the detailed spatial and temporal signatures associated with soil moisture variations on a sectional (~1-km) spatial scale, (4) developing algorithms relating C- and X-band soil moisture imagery with coincident L-band imagery for future L-band satellite development purposes, (5) developing hardware and algorithms for mitigating anthropogenic radio frequency interference in soil moisture radiometry, and (6) providing soil moisture data at field scale for land surface hydrology studies. We will present composited quick-look PSR/CX images of eight high-altitude flights conducted over two regional areas in Oklahoma during the July 2--14, 2003 period. Images show general drying in both regions interspaced with short periods of increased soil moisture following brief rainfall events.