Comparison of ship and satellite bio-optical measurements on the continental margin of the NE Gulf of Mexico

Surface flow-through data were collected three times per year from November 1997 to August 1999 from the continental margin of the NE Gulf of Mexico on hydrographic cruises that surveyed 11 cross-margin transects from the 10 m to the 1000 m isobath. These data, calibrated using standard water sampling and filtration methods, show seasonal and spatial patterns in riverine outflow and bio-optical properties. The ship data are compared with satellite estimates of sea surface temperature (Advanced Very High Resolution Radiometer (AVHRR), National Oceanic & Atmospheric Administration (NOAA)) and ocean colour (Sea-viewing-Wide-Field-of-View Sensor (SeaWiFS), Orbview II). For autumn-winter cruises, the mean relative error of satellite estimates were < ±35% for chlorophyll and coloured dissolved organic matter (CDOM) and the mean error was < +/-0.5degreesC for sea surface temperature. For spring and summer cruises, the error was larger but still < ±50% and < +/-1degreesC. The flow-through method has been found effective in estimating large-scale CDOM absorption. Correlation between CDOM and sea surface salinity was consistently high (R <-- -0.85 or higher for >7500 data points), suggesting that CDOM is a better indicator than chlorophyll to trace sea surface salinity dilution by river plumes in remotely sensed ocean colour data.