Pass the Salt: Monitoring Gulf of Mexico Near-Shore Salinity with NASA Earth Observations

Salinity estimates (shaded; blues = lower salinity, reds = higher salinity) for the Northern Gulf of Mexico on Sept. 14, 2011, derived from a combination of Moderate Resolution Imaging Spectroradiometer (MODIS) Total Suspended Sediment and Aquarius Sea-Surface Salinity products.

Team Location: John C. Stennis Space Center, Stennis, Mississippi

Shelby Barrett (William and Cary University)
Jamie Thompson (University of Southern Mississippi)
Maria Arguelles (University of Miami)

Joe Spruce (Computer Sciences Corporation, Stennis Space Center)
Kenton Ross, Ph.D. (NASA, DEVELOP National Science Advisor)
Ross Reahard (DEVELOP Stennis Center Lead)
Jason Jones (DEVELOP Stennis Assistant Center Lead)

Past/Other Contributors:
Aaron Brooks (Tulane University)
2013 Spring Brazil Oceans Team (DEVELOP, Langley Research Center)
2012 Fall Great Lakes Team (DEVELOP, Langley Research Center)


As the Mississippi River flows into the Gulf of Mexico, its freshwater plume carries approximately 550 million metric tons of sediment with it each year.  This plume sits atop the Gulf’s water column with very little mixing.  Monitoring and modeling near-shore sea surface salinity (SSS) along the Gulf Coast region is needed by fisheries managers because the plume can lead to changes in the SSS levels.  These salinity dynamics affect the vitality of multiple fisheries as well as the formation of hypoxic zones that prohibit many forms of aquatic life.  In response, this project was conducted to investigate the feasibility of improving near shore SSS estimates through combined use of total suspended solid (TSS) data derived from NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS) sensor with open water SSS measurements from Aquarius. The moderate resolution 250 meter MODIS data was inputted to an Arc Toolbox script created by the Fall 2012 Great Lakes Project at Langley Research Center. This toolbox was used to derive TSS values from the MODIS images. The coarse spatial resolution of Aquarius data collected over open water were used to derive a linear regression between its salinity estimates and the most temporally and spatially relevant available MODIS data.  The resulting linear regression equation was then applied to only MODIS data to derive a more spatially resolute estimate of SSS for coastal waters near the shore.  This data was partially validated using in situ salinity measurements acquired from multiple agencies.  This technique was applied to multiple image dates to promote a more temporally and spatially robust calibration.  The resulting data provided a much higher spatial resolution that extended closer to the shoreline than Aquarius SSS measurements alone.  The results of this project provide preliminary information on the technical feasibility of measuring SSS in the near-shore Gulf Coast waters.  These methods were communicated to a number of project partners including the Coalition to Restore Coastal Louisiana, a local nonprofit organization whose mission is the protection and restoration of a sustainable coastal Louisiana.  The project offers a potential method for the coastal zone management community to use in concert with in-situ data in the synoptic monitoring of SSS levels in near-shore coastal waters.

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