Measurement of the ocean surface in low to moderate winds at C-band

Several research flights were conducted over the Gulf of Alaska using a NOAA WP-3D aircraft to study the radar backscatter and radiative emission behavior of the ocean surface under a variety of meteorological conditions in an experiment called the Alaska Rain and Ocean Backscatter Experiment (AROBEX). Particular use was made of the University of Massachusetts C-band scatterometer (CSCAT) and multifrequency C-band radiometer aboard the WP-3D to examine microwave remote sensing techniques for the retrieval of ocean surface winds. A plethora of instrumentation onboard the aircraft was used for simultaneous measurements of surrounding environmental conditions, including a C-Band lower fuselage radar, an X-band tail Doppler radar, and GPS dropsondes. Additionally, flights were planned to take coincident measurements with the RADARSAT satellite, providing collocated synthetic aperture radar measurements of the ocean surface. An examination of these data is presented with particular emphasis on passive microwave retrieval capabilities in the low to moderate wind regime and in the presence of precipitation. GPS dropsonde profiles provide the fine tuning and ground truth information needed for a direct comparison of C-band scatterometer measurements of the ocean surface scattering and multi-frequency C-band radiometer measurements of ocean surface and atmospheric column precipitation emissions. Variability within the multi-frequency radiometer footprint is also examined through comparisons with the high resolution surface roughness measurements of simultaneous RADARSAT passes. The implications of these comparisons to remotely sensed ocean surface winds are discussed, particularly with regard to the use of satellite based passive and active microwave instrumentation.