SMAP Level 3 CAP sea surface salinity (SSS) standard mapped images contains 60-km spatial resolution SSS data averaged over a range of temporal scales. The selected dataset is the monthly mean JPL SMAP-SSS CAP version 4.2 product.

While the NASA SMAP (Soil Moisture Active Passive) mission was designed principally to measure soil moisture and freeze/thaw state from space, use of a sensitive L-band radiometer and scatterometer as in the case of Aquarius/SAC-D permits also retrieval of remotely sensed SSS observations for the world’s oceans based on extensions to the Aquarius algorithms. Salinity is a key measurement in oceanographic investigations, serving as a tracer of different water masses, aspects of circulation, and water column structure. Sea surface salinity is also an important parameter in studies of the Earth's water cycle and an indicator of the net effect of critical processes implicated, including evaporation and precipitation. Salinity is measured in units of PSU (practical salinity units), and is defined as the number of grams of salt in 1000 grams of water. The typical salinity of seawater is 35 psu with values in the open ocean varying regionally between 33 and 38 psu. More locally in coastal areas subject to riverine flows, values can be lower, with salinities in estuarine areas potentially as low as 0.5 psu.

References: Fore, A.G, S.H. Yueh, W. Tang, B.W. Stiles, and A.K. Hayashi (2016). Combined Active/Passive Retrievals of Ocean Vector Wind and Sea Surface Salinity With SMAP. IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING, VOL. 54, NO. 12. p.7396-7404. doi: 10.1109/TGRS.2016.2601486

NASA Salinity Continuity Project. 2019. JPL SMAP Level 3 CAP Sea Surface Salinity Standard Mapped Image 8-Day Running Mean V4.2 Validated Dataset. Ver. 4.2. PO.DAAC, CA, USA. doi: 10.5067/SMP42-3TPCS