REMOTE-SENSING OF OCEAN COLOR AND AEROSOL PROPERTIES - RESOLVING THE ISSUE OF AEROSOL ABSORPTION

Current atmospheric correction and aerosol retrieval algorithms for oc ean color sensors use measurements of the top-of-the-atmosphere reflec tance in the near infrared, where the contribution from the ocean is k nown for case 1 waters, to assess the aerosol optical properties. Such measurements are incapable of distinguishing between weakly and stron gly absorbing aerosols, and the atmospheric correction and aerosol ret rieval algorithms fail if the incorrect absorption properties of the a erosol are assumed. We present an algorithm that appears promising for the retrieval of in-water biophysical properties and aerosol optical properties in atmospheres containing both weakly and strongly absorbin g aerosols. By using the entire spectrum available to most ocean color instruments (412-865 nm), we simultaneously recover the ocean's bio-o ptical properties and a set of aerosol models that best describes the aerosol optical properties. The algorithm is applied to simulated situ ations that are likely to occur off the U.S. East Coast in summer when the aerosols could be of the locally generated weakly absorbing Marit ime type or of the pollution-generated strongly absorbing urban-type t ransported over the ocean by the winds. The simulations show that the algorithm behaves well in an atmosphere with either weakly or strongly absorbing aerosol. The algorithm successfully identifies absorbing ae rosols and provides close values for the aerosol optical thickness. It also provides excellent retrievals of the ocean bio-optical The algor ithm uses a bio-optical model of case 1 waters and a set of aerosol mo dels for its The relevant parameters of both the ocean and atmosphere are systematically varied to find the best (in a rms sense) fit to the measured top-of-the-atmosphere spectral reflectance. Examples are pro vided that show the algorithm's performance in the presence of errors, e.g., error in the contribution from whitecaps and error in radiometr ic calibration. (C) 1997 Optical Society of America properties. operat ion.