Aerosol Retrieval Over Ocean From DPC‐2/GF‐5(02): Using RemoTAP Extended With a 3‐Parameter Ocean Bio‐Optical Model and Comparisons With a 1‐Parameter Model

Multi‐angle polarimetric instruments (MAPs) enable the retrieval of essential aerosol properties over oceanic regions. MAPs retrieval algorithms commonly use a 1‐parameter ocean bio‐optical model (OBM), based on chlorophyll‐a concentration only to represent optical properties over open waters (case‐1), whereas the coastal water (mixture of case‐1 and case‐2 waters) representation generally requires multi‐parameter models as demonstrated for sophisticated sensors such as SPEXone. In this study, we investigated whether meaningful improvements in aerosol retrieval over coastal waters can be achieved using data from the Directional Polarization Camera DPC‐2, with a relatively limited spectral configuration, by the addition of bio‐optical degrees of freedom. To this end, the Remote Sensing of Trace Gases and Aerosol Products (RemoTAP) algorithm, developed by the Space Research Organization Netherlands (SRON), is extended by incorporating a 3‐parameter OBM to represent coastal waters. The three parameters are chlorophyll‐a concentration, backscattering coefficient of particulate matter at 660 nm, and the absorption coefficient of non‐algal particles (NAP) and colored dissolved organic matter (CDOM) at 440 nm. We applied the extended algorithm for aerosol retrieval from synthetic and real DPC‐2 observations. Results were compared with those using the 1‐parameter OBM and retrieval results from real observations were evaluated using colocated coastal AERONET data over case‐1 and case‐2 waters. The most important finding from this work is that a simple open ocean 1‐parameter OBM together with fitting a wavelength‐dependent Lambertian correction term provides sufficient accuracy for global aerosol retrieval using DPC‐2 data, even over coastal water.