Observing sea surface salinity in coastal domains using an airborne surface salinity mapper

Sea Surface Salinity directly affects the status of coastal ecosystems and serves as a tracer for seawater constituents associated with freshwater runoff. As part of an NRL-sponsored study of the dynamics of coastal buoyancy jets (CoJet), which began in July, 2000, the original Scanning Low Frequency Microwave Radiometer (SLFMR) was deployed in various coastal locations to evaluate its performance for mapping sea surface salinity, and demonstrate its application to studies of coastal plumes and buoyant jets. In a sequence of three campaigns, the radiometer was flown repeatedly over the Cheseapeake and Mobile Bay plumes and over the northern Gulf of Mexico and Florida Bay using a twin-engine Piper Navajo aircraft. Extensive surveys of sea surface salinity distributions were conducted on time scales of a few hours. The instrument was field calibrated using in situ data from oceanographic research vessels and the resulting salinity maps were corrected for known environmental influences. The logistical convenience and broad dynamic range of the instrument allowed surface maps to be generated quickly over waters that were either significantly fresher or more saline than standard seawater. The instrument performance and resulting map quality were thus found to meet the requirements of coastal oceanographic studies that are characterized by large buoyancy signals, and a variety of forcing effects that evolve relatively rapidly in time and space. The instrument and data processing system are first described and two new methods of field calibration method are presented. Examples of surface salinity maps of rapidly evolving coastal plume features are then described and interpreted using supporting in situ data. Finally, the overall capability and utility of the system is evaluated, and recent advances in the technology and future prospects are briefly considered.