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ROSES Proposals

Atmospheric Correction Over Bright Water Targets with Non-Negligible Radiances in the Near Infrared

PI: Heidi Dierssen - University of Connecticut
Many scientists working with ocean color satellite imagery are required to conduct independent or partial atmospheric correction due to high backscattering in the Near Infrared (NIR). The standard atmospheric correction algorithms typically interpret the enhanced NIR from whitecaps, coccolithophores, cyanobacteria, floating vegetation, suspended sediments, and the benthos as enhanced scattering by aerosols. This creates both omission and commission errors such that the derived water-leaving reflectance and backscattering products are decreased and the aerosol products are increased in magnitude. If the PACE mission aims to derive climate quality aerosol concentrations and ocean biogeochemistry metrics, then better methods must be developed for dealing with water with non-negligible NIR and partitioning top of the atmosphere reflectance into the appropriate streams (aerosol, whitecap, glint). Having published on a variety of bright water targets over the last 15 years, I propose to be considered for the PACE Atmospheric Correction Science Team to bridge the gap between the atmospheric and water column approaches. I currently serve on the International Ocean Colour Coordinating Group and have served on a standing committee of the Space Studies Board, as well as several strategic working groups and satellite project teams. As part of this effort, I also propose to conduct targeted field measurements to provide better estimates of elevated reflectance due to whitecaps, foam and bubbles. Modeling enhanced reflectance due to whitecaps and bubbles requires a more complex treatment than a single windspeed parameterization, which cannot capture the orders of magnitude variability between the parameters. Here, we propose to conduct local measurements of the enhancement in reflectance due to whitecaps from the ultraviolet through the short wave infrared (SWIR). Coincident measurements of bubble entrainment will be conducted, as well as host of physical and bio-optical parameters. These data will be combined with available satellite imagery to evaluate partitioning whitecaps and bubbles from various atmospheric correction schemes. Correctly estimating whitecaps could also be an important climate relevant science parameter for those studying air-sea gas exchange, generation of sea spray aerosols and potentially applicable for estimating mixed layer depth for primary productivity models. Data collected in conjunction with this field effort, and other relevant project we and others have gathered on regions prone to elevated non-negligible NIR will be compiled in an archive of coincident satellite top of the atmosphere reflectance and high quality field measurements of water leaving reflectance. Such a database can be used to evaluate approaches across a variety of challenging bright water targets where common algorithms fail.