Hyperspectral Above-Water Radiometry for Characterization of Phytoplankton Community Composition in Complex Coastal Waters

Optically complex coastal waters present a challenge for ocean color remote sensing because of the high degree of spatial heterogeneity and limitations in the performance of algorithms. Ship-based underway and fixed location hyperspectral observations of remote sensing reflectance provide a means for improved spatial resolution and greater degrees of freedom for semi-analytical algorithms. Here, we describe a series of complementary observations of surface hyperspectral radiance and irradiance and in situ measurements of apparent and inherent optical properties and key constituents in coastal waters of the northern Gulf of Mexico and southeastern Massachusetts. The Hyperspectral Surface Acquisition System (HyperSAS) was used to provide above-water measurements of radiance and irradiance in conjunction with ship-based underway sampling in the northern Gulf of Mexico and at a fixed location off coastal Massachusetts. Additional complementary measurements of in situ multispectral and above-water radiometry were also available for comparison. In addition to radiometry measurements, in situ measurements of spectral absorption and backscattering as well as spectrophotometric measurements of particulate and dissolved absorption were made using conventional methods. Observations were considered in the context of contemporaneous satellite ocean color imagery (MODIS Aqua, Suomi-NPP VIIRS). Spatial and temporal trends in optical indices of phytoplankton community composition were examined in relation to ecological and environmental drivers. Clear seasonal patterns in phytoplankton community composition were evident in both regions as well as strong spatial gradients in relation to river-influenced coastal waters in the northern Gulf of Mexico. The results illustrate the utility of above water radiometry as a complement to other methodology for characterizing phytoplankton and associated biogeochemical dynamics in optically-complex coastal regimes.