Sea-surface salinity (SSS) in the high latitudes are one of the critical links that ties up ocean, atmospheric, and cryospheric interactions and their respective roles in ocean circulation and the global water cycle. Though, polar SSS is a critical parameter, it is one of the least understood or measured parameters currently.
ESA and NASA have launched a series of passive microwave radiometry missions at L-band (1.4 GHz) to measure ocean salinity and soil moisture. ESA's SMOS (Soil Moisture Ocean Salinity), NASA's Aquarius, and SMAP (Soil Moisture Active Passive) missions have been retrieving global ocean salinities continuously. L-band radiometry measurement sensitivity at polar regions and cold waters is nearly 3-4 times less than that in warm tropical regions. As a result, currently we do not have polar salinity measurements with high sensitivity.
We will describe L-band radiometry measurements made from an airborne campaign (SASSIE) over the Beaufort Sea during September 2022, with the primary goal of salinity retrievals. We will present retrieval results of salinity and discuss other confounding factors during the retrieval process such as low cold-water sensitivity, radio frequency interference, wind-speed and SST contribution to radiometer measurements that had to be corrected for salinity retrieval. We used the Klein-Swift salinity model to convert radiometric brightness temperature (Tb) to salinity.
Another, technique to improve sensitivity in cold-waters is to measure at frequencies lower than 1.4 GHz. As the frequency decreases, the sensitivity of Tb to salinity increases at colder water temperatures. We will present modeling results that demonstrate the potential retrievals possible with lower frequency radiometers, and associated error statistics of derived salinity.
We will also briefly present a wide-band radiometer (LOBSTER) built from 1.1-1.7 GHz and deployed in a ground-based experiment observing the Piscataqua River flowing into the Atlantic Ocean during the winter of March 2023. The daily tides, allowed a daily large dynamic salinity range to be observed by the instrument at temperatures as cold as 2 degree C. We will present initial salinity retrieval results at these frequencies.