Improving the operational coverage of MISR aerosol retrievals over shallow, turbid, and eutrophic waters

Abstract

<p>Shallow coastal waters are often biologically productive (eutrophic), turbidity from runoff is common, and the atmosphere above is typically more aerosol-laden than over open ocean waters. Although the NASA Earth Observing System’s Multi-angle Imaging SpectroRadiometer (MISR) onboard the Terra satellite has been observing aerosols for 23 years, the current operational retrieval algorithm (V23) does not report results over shallow waters (< 50 m in depth or < 5 km from land), due to the complexity of accounting for water-leaving radiance under these conditions. However, MISR measures radiances at four wavelengths and nine view angles, which makes it possible to distinguish atmospheric from ocean surface contributions to the top-of-atmosphere signal. Here, we implement and validate a "Shallow Water" aerosol retrieval algorithm, following Limbacher and Kahn (2019), which constrains a Lambertian surface reflectivity term to account for water-leaving radiance from shallow, turbid, and eutrophic waters. We develop custom quality filtering and find that this modified retrieval algorithm compares well to independent surface-based observations and is better suited for use over shallow waters than the operational Dark Water retrieval algorithm. Globally, retrieving aerosols over shallow waters increases the number of over-water measurements by more than 7%, preferentially in some of the most biologically active coastal regions of the ocean.</p>