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Abstract. Coastal waters serve as transport pathways to the ocean for all agriculturaland other runoff from terrestrial sources, and many are the sites forupwelling of nutrient-rich, deep water; they are also some of the mostbiologically productive on Earth. Estimating the impact coastal waters haveon the global carbon budget requires relating satellite-based remote-sensingretrievals of biological productivity (e.g., chlorophyll  a concentration)to in situ measurements taken in near-surface waters. The Multi-angle ImagingSpectroRadiometer (MISR) can uniquely constrain the “atmosphericcorrection” needed to derive ocean color from remote-sensing imagers. Here,we retrieve aerosol amount and type from MISR over all types of water. Theprimary limitation is an upper bound on aerosol optical depth (AOD), as thealgorithm must be able to distinguish the surface. This updated MISR researchaerosol retrieval algorithm (RA) also assumes that light reflection by theunderlying ocean surface is Lambertian. The RA computes the ocean surfacereflectance ( Rrs ) analytically for a given AOD, aerosol opticalmodel, and wind speed. We provide retrieval examples over shallow, turbid, and eutrophic waters andintroduce a productivity and turbidity index (PTI), calculated from retrievedspectral Rrs , that distinguished water types (similar to the the normalized difference vegetation index,NDVI, over land). We also validate the new algorithm by comparing spectral AOD andAngstrom exponent (ANG) results with 2419 collocated AErosol RObotic NETwork (AERONET)observations. For AERONET 558 nm interpolatedAOD   1.0, the root-mean-square error (RMSE) is 0.04 and linearcorrelation coefficient is 0.95. For the 502 cloud-free MISR and AERONETcollocations with an AERONET AOD  >  0.20, the ANG RMSE is 0.25 and r is 0.89. Although MISR RA AOD retrieval quality does not appear to besubstantially impacted by the presence of turbid water, the MISR-RA-retrievedAngstrom exponent seems to suffer from increased uncertainty undersuch conditions. MISR supplements current ocean color sources in regions where sunglintprecludes retrievals from single-view-angle instruments. MISR atmosphericcorrection should also be more robust than that derived from single-viewinstruments such as the Moderate Resolution Imaging Spectroradiometer (MODIS).This is especially true in regions of shallow,turbid, and eutrophic waters, locations where biological productivity can behigh, and single-view-angle retrieval algorithms struggle to separateatmospheric from oceanic features.

atmospheric measurement techniques

Updated MISR over-water research aerosol retrieval algorithm – Part 2: A multi-angle aerosol retrieval algorithm for shallow, turbid, oligotrophic, and eutrophic waters