Presented at the 2013 SMOS-Aquarius Science WorkshopValidating satellite remote sensing data against in situ measurements is always a complex task. For the Aquarius and SMOS salinity satellites, one additional challenge arises due to the fact that the salinity value retrieved from the satellite observations represents salinity at a "skin" depth no more than a few centimeters below the sea surface, while the validation data sets are usually collected at the "bulk" depth of several meters below the sea surface. The "skin-bulk" salinity difference can be as large as 0.2 psu, comparable to the accuracy requirement established by the Aquarius satellite mission.Salinity Processes in the Upper Ocean Regional Study (SPURS) research effort is actively addressing essential role of the ocean in the global water cycle. A series of cruises is exploring the salinity maximum region in the Atlantic Ocean using a plethora of oceanographic equipment and technology, including salinity-sensing satellites. Researchers are studying salinity changes that span thousands of miles simultaneously with those happening in one centimeter of water. SPURS is also providing much-needed data for computer models to improve our basic understanding of the water cycle over the oceans and its ties to climate.To quantify the "skin-bulk" difference of salinity, this talk will analyze the upper ocean salinity stratification using in situ measurements collected from the SPURS (Salinity Processes in the Upper Ocean Regional Study) field experiment during September-October 2012. A variety of in situ platforms were deployed during the 33-day cruise. The wave glider measures salinity at 0.2 m. Surface drifting buoys (i.e., drifters) measure salinity at 0.6 m below the sea surface. While conventional profiling floats stop measuring salinity at about 5 m, the newly developed STS (Surface Temperature/Salinity) floats can measure salinity all the way to the skin layer close to the surface. Results describing the upper ocean salinity stratification from these in situ data and their comparisons with the Aquarius data will be presented.