Optical scattering and backscattering by organic and inorganic particulates in US coastal waters

Code 7230, US Naval Research Laboratory, Washington, DC 20375-5320, USA.
Applied Optics (Impact Factor: 1.78). 03/2008; 47(5):666-77. DOI: 10.1364/AO.47.000666
Source: PubMed


We present the results of a study of optical scattering and backscattering of particulates for three coastal sites that represent a wide range of optical properties that are found in U.S. near-shore waters. The 6000 scattering and backscattering spectra collected for this study can be well approximated by a power-law function of wavelength. The power-law exponent for particulate scattering changes dramatically from site to site (and within each site) compared with particulate backscattering where all the spectra, except possibly the very clearest waters, cluster around a single wavelength power-law exponent of -0.94. The particulate backscattering-to-scattering ratio (the backscattering ratio) displays a wide range in wavelength dependence. This result is not consistent with scattering models that describe the bulk composition of water as a uniform mix of homogeneous spherical particles with a Junge-like power-law distribution over all particle sizes. Simultaneous particulate organic matter (POM) and particulate inorganic matter (PIM) measurements are available for some of our optical measurements, and site-averaged POM and PIM mass-specific cross sections for scattering and backscattering can be derived. Cross sections for organic and inorganic material differ at each site, and the relative contribution of organic and inorganic material to scattering and backscattering depends differently at each site on the relative amount of material that is present.

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Available from: Michael Sydor, Nov 22, 2014
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    • "Spectral shape parameters Y, ζ, and ξ For practical reasons, Y, the spectral slope of in situ measurements of b bp , was estimated in LIS from the spectral slope of b p as described in Aurin et al. (2010). This approach assumed a spectrally independent backscattering ratio and was supported by Mie theory (Ulloa et al., 1994) and field data (Whitmire et al., 2007), although studies have challenged this assumption for natural waters (McKee & Cunningham, 2005; Snyder et al., 2008), and more extensive multi-spectral measurements of b bp in LIS are clearly warranted. Y has been shown to be related to the particle size distribution, whereby polydispersions of larger particles such as those found in coastal and estuarine waters tend to lead to a weaker spectral dependence in b bp (Babin et al., 2003; Morel & Ahn, 1990), although empirical corroboration remains limited. "
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