The Salinity Processes in the Upper Ocean Regional Study (SPURS) project is a NASA-funded oceanographic campaign aimed at elucidating key mechanisms responsible for near-surface salinity variations in the ocean. Over the period August 2016 through November 2017, SPURS-2 deployed a suite of in situ sampling technologies to study a low-salinity, high precipitation region in the eastern tropical Pacific, including the state-of-the-art wind and solar powered unmanned surface vehicle (USV) called Saildrone. Saildrone provides observations of salinity, temperature, and other variables that enables 1) a new platform to support remote sensing validation and 2) detailed characterization of oceanic structure over a continuum of spatio-temporal scales when combined with remote sensing data.
The following animation provides a comparison of Saildrone sea surface salinity (SSS) and satellite SMAP SSS, as well as Saildrone sea surface temperature (SST) and satellite MUR SST during the SPURS-2 campaign. The animation illustrates good agreement between satellite-derived and in situ data. Variations between SSS datasets are likely the result of different spatio-temporal resolutions and higher patchiness in surface salinity signatures due to rain events and other processes. Saildrone provides high frequency observations (sub-minute resolution) at the local scale and SMAP at 70 km resolution with an eight day precise orbital repeat, or 3 day partial swath coverage overlap. The coarser SMAP resolution smooths the SSS signal in the domain, as demonstrated by the inability of SMAP SSS to reproduce Saildrone SSS peaks and valleys associated with higher variability. Deviations between SST datasets can be explained by unresolved daily variability, wherein MUR only uses nighttime data.