Optimizing Performance of a Microwave Salinity Mapper: STARRS L-Band Radiometer Enhancements

Abstract

Airborne microwave radiometers for salinity remote sensing have advanced to a point where operational surveys can be conducted over the inner continental shelf to observe the evolution of freshwater plumes emanating from rivers and estuaries. To determine seawater microwave emissivity, and hence conductivity and salinity, precisely and accurately demands high instrument sensitivity, stability, and sampling rates; such requirements involve significant design trade-offs. The Salinity, Temperature, and Roughness Remote Scanner (STARRS) was developed to enhance these features relative to existing instruments. The authors describe here key elements of the STARRS design and the results of early performance assessments and deployments. During early deployments, the instrument performed well in areas of moderate to high salinity signal-to-noise ratio, but more homogenous areas revealed band-limited random signal fluctuations on the order of a 6-min period and ?1-K amplitude that were of internal origin. Detailed analyses of laboratory and field tests revealed that internal ?flicker,? or 1/f noise (having spectral roll-off proportional to the reciprocal of frequency f?), was the main source of these fluctuations. The instrument was modified to eliminate the random fluctuations and to further enhance sensitivity and stability. Laboratory tests and recent field deployments show that the upgrade improved instrument performance dramatically, to the extent that continental shelf scale areas with relatively homogenous salinity distributions can now be surveyed reliably using STARRS.