|Paper title||Salinity Retrievals near the Sea-Ice Edge using Multi-Spectral Channel Infor-mation from SMAP and AMSR2|
|Form of presentation||Poster|
Retrieving sea-surface salinity near the sea-ice edge using spaceborne L-band radiometers (SMOS, Aquarius, SMAP) is a challenging task. There are several reasons for this. First, in cold water, the sensitivity of the L-band emitted surface brightness temperature to salinity is small, which results in large retrieval errors. Additionally, it is diffi-cult to both detect the sea-ice edge and accurately measure small sea-ice concentrations near the sea-ice edge. We have evaluated several publicly available sea-ice con-centration products (OSI-SAF, NSIDC CDC, NCEP) and found that none of them meet the accuracy that is required to use them as ancillary input for satellite salinity retriev-als. This constitutes a major obstacle in satellite salinity measurements near the sea-ice edge. As a consequence, in the cur-rent NASA/RSS V4.0 SMAP salinity release, salinity cannot be retrieved over large areas of the polar oceans.
We have developed a mitigation strategy that directly uses AMSR2 TB measurements of the 6 – 36 GHz channels to assess the sea-ice contamination within the SMAP antenna field of view instead of external ancillary sea-ice concentration products. The 6 and 10 GHz AMSR2 TB show very good correlation with the SMAP TB when averaged over several days. Moreover, the spatial resolutions of AMSR2 6 GHz and SMAP TB measurements are very comparable.
Based on this, we have developed a machine-learning algorithm that uses the AMSR2 and SMAP TB as input (1) to detect low sea-ice concentrations within the SMAP foot-print and (2) that allows to remove the sea-ice fraction from the SMAP measurements.
This new algorithm allows for more accurate sea-ice detection and mitigation in the SMAP salinity retrievals than the ancillary ice products do. In particular, the detection of icebergs in the polar ocean and salinity retrievals in the vicinity of sea-ice can be significantly improved. We plan to apply this new method in the upcoming NASA/RSS V5.0 SMAP salinity release.