Wednesday, June 30, 2021

The PO.DAAC is pleased to announce the release of the Multi-Mission Optimally Interpolated Sea Surface Salinity (OISSS) Level 4 V1.0 dataset. This dataset grids the Level-2 orbital swath data from the AQUARIUS/SAC-D mission (25 August 2011 to 7 June 2015), the Soil Moisture Active Passive (SMAP) mission (April, 2015 - present) and Soil Moisture and Ocean Salinity (SMOS) onto a 0.25-degree spatial and 4-day temporal grid using Optimal Interpolation (OI) . The product is available from August 28, 2011 to present. Three years and 9 months of AQUARIUS data were used between August 28, 2011 and June 7, 2015. SMAP data, available since April 2015, extends the product to present. The two-month overlap between Aquarius and SMAP was used to ensure consistency and continuity in data record. SMOS data were used only to fill the SMAP data gap during 19 June – 24 July, 2019, when the SMAP satellite was in a safe mode.

The product covers the global ocean, including the Arctic and Antarctic in the areas free of sea ice, but does not cover internal seas, such as the Mediterranean and the Baltic Sea. It has been evaluated against in-situ data from Argo floats and moored buoys for error quantification. The global mean root-mean-square difference between the OISSS and concurrent in-situ data is around 0.19 psu. The in-situ data are also used for satellite large-scale bias correction, which results in near-zero bias in OISSS. The estimated spatial feature resolution of the gridded fields is about 125 km derived by comparing the meridional wavenumber spectra of the AQUARIUS OISSS and SMAP OISSS. The product follows CF/ACDD metadata conventions and includes an estimated SSS uncertainty field.

The multi-mission OISSS Level 4 V1.0 dataset is produced by the International Pacific Research Center (IPRC), University of Hawaii at Manoa in collaboration with Remote Sensing Systems (RSS), Santa Rosa, California, who provided SMAP L2 data. It is discoverable and accessible via the PO.DAAC data portal. More details about this product, including the OI methodology, product validation, and uncertainty quantification etc. can be found in its technical documentation (user guide). General information regarding the Aquarius, SMAP and SMOS missions are available from the respective mission websites.




Oleg Melnichenko, Peter Hacker, James Potemra, Thomas Meissner, and Frank Wentz (2021). Aquarius/SMAP sea surface salinity optimum interpolation analysis, IPRC Technical Note No. 7, May 7, 2021.


Melnichenko, O., P. Hacker, N. Maximenko, G. Lagerloef, and J. Potemra, 2014: Spatial Optimal Interpolation of Aquarius Sea Surface Salinity: Algorithms and Implementation in the North Atlantic, J. Atmos. Oceanic Technol., 31, 1583-1600.

Melnichenko, O., P. Hacker, N. Maximenko, G. Lagerloef, and J. Potemra, 2016: Optimum interpolation analysis of Aquarius sea surface salinity, J. Geophys. Res. Oceans, 121, 602-616, doi:10.1002/2015JC011343.

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