Abstract
The effects of non-nadir viewing geometry in above-water radiometry data were investigated using field measurements and two different correction approaches: one centered on chlorophyll-a concentration (Chla) developed for Case-1 waters, and the other relying on seawater inherent optical properties (IOP) proposed for any water type. With specific reference to data from the Ocean Color component of the AErosol RObotic NETwork (AERONET-OC), the study focused on the assessment of the uncertainties affecting corrections for non-nadir view of data collected with 40° in-air viewing angle and with 90° relative azimuth between viewing direction and sun. The study analyzed AERONET-OC water-leaving radiance data from different European seas to determine differences between corrections performed with the Chla- and the IOP-based approaches. Additionally, data collected in waters characterized by different optical complexity and comprising water-leaving radiances measured at nadir and with 28.6° in-water viewing angle (corresponding to 40° in-air) and 90° relative azimuth, were used to investigate the uncertainties of the two correction approaches. Results from the analysis of data from AERONET-OC sites characterized by a variety of optically complex waters, indicate corrections with uncertainties between 20% and 35% from 412 nm to 667 nm for the IOP-based approach. Conversely, uncertainties for the Chla-based one largely vary with wavelength and water type, with values of approximately 55% at 412 nm, 20-40% between 490 nm and 551 nm, and exceeding 60% at 667 nm.
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