Atmospheric Correction for Satellite Ocean Color Radiometry * * * * * * * * A Tutorial and Documentation of the Algorithms Used by the NASA Ocean Biology Processing Group

This tutorial is an introduction to atmospheric correction in general and also documentation of the atmospheric correction algorithms currently implemented by the NASA Ocean Biology Processing Group (OBPG) for processing ocean color data from satellite-borne sensors such as MODIS and VIIRS. The intended audience is graduate students or others who are encountering this topic for the first time. The tutorial is in two parts. Part I discusses the generic atmospheric correction problem. The magnitude and nature of the problem are first illustrated with numerical results generated by a coupled ocean-atmosphere radiative transfer model. That code allow the various contributions (Rayleigh and aerosol path radiance, surface reflectance, water-leaving radiance, etc.) to the topof-the-atmosphere (TOA) radiance to be separated out. Particular attention is then paid to the definition, calculation, and interpretation of the so-called “exact normalized water-leaving radiance” and its equivalent reflectance. Part I ends with chapters on the calculation of direct and diffuse atmospheric transmittances, and on how vicarious calibration is performed. Part II then describes one by one the particular algorithms currently used by the OBPG to effect the various steps of the atmospheric correction process, viz. the corrections for absorption and scattering by gases and aerosols, Sun and sky reflectance by the sea surface and whitecaps, and finally corrections for sensor out-of-band response and polarization effects. One goal of the tutorial—guided by teaching needs— is to distill the results of dozens of papers published over several decades of research in atmospheric correction for ocean color remote sensing. Any subsequent modifications to the originally published techniques are noted in the documentation. This content of this tutorial is available online as the Atmospheric Correction chapter of the Ocean Optics Web Book, beginning at http://www. oceanopticsbook.info/view/atmospheric_correction/chapter_overview. A pdf version of the report can be downloaded as Mobley et al. (2016) in the publications section of the Ocean Optics Web Book.

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