Polarized Shipboard LIDAR Ocean Profiler for Subsurface Bio-Optical Layer Characterization

A shipboard Nd-Yag LIDAR with the ability to measure co- and cross- linear and circular polarization has been deployed in several oceanic conditions to examine the ability to detect subsurface optical layers and characterize their corresponding particles. The system has a vertical resolution of 0.20 meters and can resolve up to depths of approximately 2 diffuse attenuation lengths. Deployments include environments with strong and weak bio-optical layers (East Sound, WA), a coastal frontal boundary, and Lake Erie during an extensive harmful algae bloom. Change in the polarization return for each mode within these environments is shown to provide information on particle mixing dynamics demonstrated by variation in the co and cross polarization during the evolution and break-up of a bio-optical layer associated with the passage of a tidal front. The differences in the linear and circular polarization return and ability to use these measurements to characterize particles is evaluated for environments that include small phytoplankton in gelatinous masses (Microcystis), long chains (Planktothrix), helical chains (Anabaena), and long (up to 2 mm) of oriented chains (Ditylum). While some differences between depolarization and the magnitude of co and cross linear versus circular polarization states are observed there is weak evidence that information about particle composition, size, and shape is provided in the polarized LIDAR data.