Atmospheric correction of ocean colour rs observations (2)

IOCCG Summer Lecture Series 2012

This lecture will provide an overview of atmospheric correction approaches for remote sensing of water properties for open oceans and coastal waters. Beginning with definitions of some basic parameters for describing ocean and atmosphere properties, the radiative transfer equation (RTE) for ocean?atmosphere system will be introduced and discussed. Various methods for solving RTE, in particular, the successive?order?of?scattering method will be described. We examine various radiance contribution terms in atmospheric correction, i.e., Rayleigh scattering radiance, aerosol radiance (including Rayleigh?aerosol interaction), whitecap radiance, sun glint, and water?leaving radiance. Atmospheric correction algorithms using the near?infrared (NIR) and shortwave infrared (SWIR) bands will be described in detail, as well as some examples from MODIS?Aqua measurements. The standard NIR atmospheric correction algorithm has been used for deriving accurate ocean color products over open oceans for various satellite ocean color sensors, e.g., OCTS, SeaWiFS, MODIS, MERIS, VIIRS, etc. Some specific issues of atmospheric correction algorithm over coastal and inland waters, e.g., highly turbid and complex waters, strongly absorbing aerosols, will also be discussed. The outline of the lectures is provided below. Outline of the Lectures Introduction Brief history Basic concept of ocean color measurements Why need atmospheric correction Radiometry and optical properties Basic radiometric quantities Apparent optical properties (AOPs) Inherent optical properties (IOPs) Optical properties of the atmosphere Molecular absorption and scattering Aerosol properties and models Non? and weakly absorbing aerosols Strongly absorbing aerosols (dust, smoke, etc.) Radiative Transfer Radiative Transfer Equation (RTE) Various approaches for solving RTE Successive?order?of?scattering method Single?scattering approximation Sea surface effects Atmospheric diffuse transmittance Normalized water?leaving radiance Atmospheric Correction Define reflectance and examine the various terms Single?scattering approximation Aerosol multiple?scattering effects Open ocean cases: using NIR bands for atmospheric correction Coastal and inland waters Brief overviews of various approaches The SWIR?based atmospheric correction Examples from MODIS?Aqua measurements Addressing the strongly?absorbing aerosol issue The issue of the strongly?absorbing aerosols Some approaches for dealing with absorbing aerosols Examples of atmospheric correction for dust aerosols using MODIS?Aqua and CALIPSO data Requirements for future ocean color satellite sensors Summary Bibliography Chandrasekhar, S. (1950), “Radiative Transfer,” Oxford University Press, Oxford, 393 pp. Van de Hulst, H. C. (1980), “Multiple Light Scattering,” Academic Press, New York, 739pp. Gordon, H. R. and A. Morel (1983), “Remote Assessment of Ocean Color for Interpretation of Satellite Visible Imagery: A Review,” Springer?Verlag, New York, 114pp. Gordon, H. R. and M. Wang (1994), “Retrieval of water?leaving radiance and aerosol optical thickness over the oceans with SeaWiFS: A preliminary algorithm,” Appl. Opt., 33, 443?452. Gordon, H. R. (1997), “Atmospheric correction of ocean color imagery in the Earth Observing System era,” J. Geophys. Res., 102, 17081?17106. Wang, M. (2007), “Remote sensing of the ocean contributions from ultraviolet to near?infrared using the shortwave infrared bands: simulations,” Appl. Opt., 46, 1535?1547. IOCCG (2010), “Atmospheric Correction for Remotely?Sensed Ocean?Color Products,” Wang, M. (ed.), Reports of International Ocean?Color Coordinating Group, No. 10, IOCCG, Dartmouth, Canada. (http://www.ioccg.org/reports_ioccg.html)