L-band microwave observations over land surface using a two-dimensional synthetic aperture radiometer

Antenna size is a major factor that has limited realization of the potential capabilities of L-band (1.4 GHz) microwave radiometry to estimate surface soil moisture from space. However, emerging interferometric technology, called aperture synthesis, has been developed to address this limitation. The Soil Moisture and Ocean Salinity (SMOS) mission will apply the technique to monitor these parameters at a global- scale in the near future. The first airborne experiment using an aircraft prototype called the Two-Dimensional Synthetic Aperture Radiometer (2D- STAR) was performed during Soil Moisture Experiment in 2003 (SMEX03). To gain insight, the L- band brightness temperature data acquired by 2D-STAR in Alabama was compared with C-band data collected simultaneously by another aircraft instrument called the Polarimetric Scanning Radiometer ( PSR), and also compared with surface soil moisture measurements from in- situ observations sites. Results show that there was fairly good radiometric sensitivity of the synthetic aperture radiometer to the soil moisture both in pasture and also in forest areas. The overall performance of the L-band synthetic aperture radiometer in the presence of vegetation appears to be better than the C-band real aperture radiometer.