Utilising the Vibrational-Raman-Scattering signal of Oceanic Waters in Hyperspectral Satellite Measurements.
Dinter, Tilman1; Rozanov, V.1; Wolanin, A.1; Taylor, B.2; Soppa, M.2; Bracher, A.2; Burrows, J.P.1
1Institute of Environmental Physics, University of Bremen, GERMANY; 2Alfred-Wegener-Insitute for Polar and Marine Research, GERMANY
The determination of the penetration depth of solar light into oceanic waters from satellite remote sensing data is still a challenging and high defective task. The most widely used value for the availability of light in the water column is the diffuse attenuation coefficient for downwelling solar radiation Kd(z,λ).
In this study a new approach to retrieve the diffuse attenuation coefficient of oceanic waters based on the spectral signatures of Vibrational Raman Scattering (VRS) detected in hyper-spectral satellite data is introduced. VRS is an inelastic scattering effect of the water itself where energy is transported from the photon to the molecule during the scattering process to excite the water molecule to vibrations (Stokes lines, anti-Stokes lines are neglected). The emitted photon has another energy, i.e. a different wavelength. As a transpectral process VRS contributes significantly to the filling-in of solar Fraunhofer lines. This signal is clearly identified in hyper-spectral satellite measurements, as shown for data of the satellite sensor SCIAMACHY and was exploited as a proxy for the radiation availability in the ocean column [Vountas et al., 2007]. Therefore we directly connect the strength of the VRS signal in SCIAMACHY measurements to the diffuse attenuation coefficient Kd. No further knowledge on the absorption and scattering coefficients of water constituents (IOPs) are required. To model the relationship between VRS and Kd extensive radiative transfer calculations with the coupled ocean-atmosphere RTM SCIATRAN [Rozanov et al., 2002;Blum et al., 2012] have been performed. Comparisons with the MERIS GlobColour Kd(490) product shows reliable agreement between this two completely different approaches.
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