Remote sensing of coastal salinity: naval needs and developing capability

Inability to routinely map sea surface salinity (SSS) has often prevented accurate analysis and prediction of ocean surface features. In the open ocean, precipitation and evaporation create horizontal and vertical gradients of salinity that impact buoyant mixing and heat and moisture exchange with the atmosphere. Thin lenses of fresh or saline water at the surface can confuse satellite derived estimates of air-sea fluxes and create a significant bias in the lower boundary condition provided to operational atmospheric prediction models. Estimates of the ocean vertical structure are often derived largely from remote sensing of ocean surface parameters. Great strides have recently been made in the assimilation of altimeter heights and infrared sea surface temperature (SST) observations. However, density gradients due to salinity are rarely identified by these observations and can lead to erroneous extrapolation of surface conditions into the interior of the ocean. Coastal sources of fresh water greatly complicate salinity structure in the littoral. The Salinity Temperature and Roughness Remote Scanner (STARRS) has been designed to make the primary L-band measurement with about six times lower noise levels than SLFMR. It is of a pushbroom design allowing longer integration times. It has improved antenna loss characteristics and needs less time for internal calibration. It also includes an improved IR sensor for SST which is required for salinity retrieval. Sea surface roughness is also a significant factor in salinity retrieval but was not measured by SLFMR. STARRS will include a multifrequency C-band radiometer for that purpose.