What can polarized oceanographic lidar reveal about ocean particle assemblages? Insights from a mesoscale coccolithophore bloom.

Brian Collister, NASA Langley Research Center, Hampton, VA, United States, Richard Carl Zimmerman, Old Dominion University, Ocean, Earth, & Atmospheic Sciences, Norfolk, VA, United States, Victoria J Hill, Old Dominion University, Ocean, Earth, & Atmospheric Science, Norfolk, VA, United States, Charles I Sukenik, Old Dominion University, Physics, Norfolk, VA, United States and William M Balch, Bigelow Laboratory for Ocean Sciences, East Boothbay, ME, United States
Oceanographic lidar is a remote sensing technique that can measure vertical profiles of optical properties in the upper ocean. When related to the biogeochemical properties of materials in the ocean, these measurements have the potential to greatly improve our ability to investigate processes controlling the production, transport, and transformation of ocean particles. While most oceanographic lidar investigations have focused on inversion of the lidar attenuation (Ksys) and backscattering coefficients to retrieve estimates of particle concentration (e.g. chlorophyll, particulate organic carbon [POC]), recent experimental and theoretical evidence suggests that the extent to which the lidar return signal is depolarized, the lidar depolarization ratio (σ), may provide information on the intrinsic properties of the particle assemblage (i.e. shape, size, composition). To explore this capability further, a polarized oceanographic lidar was deployed from the R/V Endeavor during a research expedition (Coccomix 2018) to sample the New England mesoscale coccolithophore bloom. Throughout the expedition, measurements of Ksys and σ were made in parallel with underway measurements of inherent optical properties using a flow-through optics package, and above-water radiometric measurements using a HyperSAS radiometer system mounted to a solar tracker at the bow. Vertical profiles of particulate backscatter and downwelling irradiance were measured at nine discrete stations, alongside of a variety of biogeochemically relevant properties of the particle assemblage including [POC], particulate inorganic carbon, coccolithophore and free coccolith abundance, and FlowCam measurements of particle shape and size. Characterization of the lidar return signal response to the diverse array of particle and optical properties encountered as we transited the bloom lead to a greater understanding of the ability for polarized oceanographic lidar to characterize complex ocean particle assemblages.