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Pass the Salt: Monitoring Gulf of Mexico Near-Shore Salinity with NASA Earth Observations
>> [Shelby]: I'm Shelby Barrett, and I attend William and Cary University.
>> [Jamie]: My name is Jamie Thompson, and I attend the University of Southern Mississippi.
>> [Maria]: My name is Maria Arguelles, and I attend the University of Miami.
>> [Shelby]: This project focuses on improving estimations of sea surface salinity in near-shore
environments through the use of NASA remote sensing.
>> [Shelby]: Our study area focuses on the Northern Gulf of Mexico, specifically the
Louisiana and Mississippi coastal waters near the mouth of the Mississippi and Atchafalaya
Rivers.
>> [Jamie]: Monitoring salinity here is important because the Mississippi-Atchafalaya River
systems collectively drain 40% of the continental US, which affects the Gulf�s coastal salt
concentration. Since salt water is denser than freshwater, the river output sits atop
the water column with little mixing near shore.
>> [Maria]: Gulf of Mexico coastal salinity is currently observed using in situ monitoring
data collected by buoys, drifter instruments, and shipboard instruments. This can become
costly and can be affected by biofouling.
>> [Dr. Stephen D. Howden]: Salinity, along with temperature and pressure, control the
density of the water. And the density of the water, variations of the density of the water,
can affect how well, how easily water can be mixed vertically. Which in the Gulf of
Mexico is important for phenomena such as hypoxia, or when bottom DO gets very low to
where many marine animals can't survive.
>> [Dr. Stephen D. Howden]: It's very costly to maintain a conductivity sensor, it costs
more than thermistors and, they cost more to maintain, and then you have to calibrate
them. So it's a lot more difficult to get funding to have a whole lot of conductivity
cells for measuring salinity.
>> [Dr. Stephen D. Howden]: Remote sensing is a way, is a good way, to get, if you can
measure salinity, to measure it over the whole Gulf of Mexico or the whole world ocean.
>> [Shelby]: The Aquarius sensor on board the SAC-D satellite was utilized for its salinity
data, which was collected from the Ocean Color Web database. The MODIS sensor onboard the
Aqua and Terra satellites weas used to create estimates of total suspended solids, or TSS,
using MODIS images from the USGS GloVis interface.
>> [Maria]: Once the MODIS images were acquired, specific bands were selected to run through
a model created in a previous DEVELOP term to create a TSS raster in ArcMap.
>> [Jamie]: Next, the Aquarius data was made into an easy to use format for ArcMap to plot
the points of the Aquarius measurements. A raster was created from these points and was
resampled to match the pixel size of the MODIS raster. Both the TSS and Aquarius rasters
were then cut to one another in order to compare the overlapping points on a graph. A linear
regression was run on the graph and the equation of the line of best fit was used in ArcMap�s
raster calculator with the un-cut TSS image to calculate a new map of derived salinity.
>> [Shelby]: In situ data was then downloaded from the World Ocean Database and Gulf of
Mexico Coastal Ocean Observing System. This data was plotted in ArcMap over our derived
salinity estimations in order to validate our results.
>> [Maria]: 18 maps of calculated Sea Surface Salinity from August 2011 to May 2013 were
created using available cloud free MODIS imagery that lined up with Aquarius data. Most of
these showed reasonable near-shore salinity values, showing promise in our methodology
with appropriate TSS models for specific locations.
>> [Jamie]: Statistics were also created for all 18 days to see the relation between our
calculated salinity and in situ measurements.