A Next Generation Microwave Instrument for Cold Water Salinity Measurement
[14-Dec-2018] Misra, S., Ramos, I., Felten, C., Bosch-Lluis, J., Brown, S.T., Yueh, S.H., Latham, B., and Lee, T.
Presented at the 2018 AGU Fall Meeting
NASA's Aquarius and SMAP (Soil Moisture Active Passive) missions operating at 1.4 GHz (L-band) successfully demonstrated the ability to measure sea-surface salinity (SSS) at a high precision. Though successful, a narrow band-width of 24 MHz on both of the passive sensors limited retrievals of sea-surface salinity to global regions with warmer sea-surface temperatures, due to reduced SSS sensitivity at L-band at lower sea surface temperatures (SST). A narrow bandwidth also requires external ancillary wind speed (WS) and sea surface temperature (SST) data to inform the retrieval algorithms.
Thus, there exists an observing system capability gap with respect to SSS at SST less than 5°C. This observation gap limits our ability to study the interface between the ocean and cryosphere over the polar regions. Sea water freshening around the polar regions has a direct link to polar ice melting, sea ice forecast and thus sea level projections.
In order to overcome such measurement limitations, low microwave frequency radiometric measurements around 500 MHz (P-band) that have a theoretical sensitivity of nearly 3 times that of L-band are required. Continuous measurements from P- to L-band also enable concurrent retrieval of WS and SST without the need of any ancillary information.
We will present a JPL developed polarimetric wideband prototype active/passive microwave sensor that currently operates from 500 MHz to 1.5 GHz. The instrument has been developed for airborne as well as ship-borne measurements. We will discuss instrument design challenges in order to develop such a wide-band instrument. These challenges include developing a continuous wide-band RF system with digital backend capable of ingesting a GHz of signal, ability to deal with man-made interference operating at frequencies within the bandwidth, integrating an active channel within a passive radiometer band.
We will present preliminary field campaign measurements of ship based cold-water salinity retrievals made during an Arctic Ocean campaign. These campaign results will compare passive retrievals of SSS with in-situ
measurements made over large range of SSS, SST and WS conditions. The ship cruise will occur during the months of September-October 2018 from Alaska to the Beaufort Sea. These measurements represent a new microwave remote sensing technique.