Hyperspectral Remote Sensing of the Amazon River Plume

The Amazon River is the largest river in the world and discharges more than 200,000 m³ s^-1 into the Western Tropical North Atlantic Ocean. At its peak, the low salinity plume extends more than 2000 km from the mouth and overs an area greater than 1 million square kilometers. Hyperspectral remote sensing measurements of downwelling irradiance and water-leaving radiance using the Sky Blocked Approach (SBA) were made in the Amazon River plume and surrounding oceanic waters during a field survey in May 2019. These measurements were quality controlled using a tilt filter to remove measurements that exceed a 5 degree tilt threshold from nadir and an outlier filter that removed artifacts such as the cone of the SBA being completely out of water or submerged. Over 4000 measurements were acquired at each station and the rigorous quality control resulted in about 1% of these measurements to be used for subsequent analysis. The particulate and dissolved absorption spectra and HPLC diagnostic pigments were also measured at the same locations. The Quasi-Analytical Algorithm and OC4 with SeaWiFS coefficients were used to derive bio-optical parameters. Comparison with results derived from the spectra and in situ measurements of particulate absorption, colored dissolved organic matter and diagnostics phytoplankton pigments is presented.