A convolution algorithm of differential coefficients of liquid water based on vibrational Raman scattering

Abstract

Inelastic vibrational Raman scattering by liquid water is one significant limitation to the accuracy of the retrieval of trace gas constituents in atmosphere over waters, particularly over clear ocean waters, while using satellite data with differential optical absorption spectroscopy technique (DOAS). The effect which is similar to the Ring effect in atmosphere results in the filling-in of Fraunhofer lines, which is known as solar absorption lines. The inelastic component of the liquid water scattering causes a net increase of radiance in the line because more radiations shift to the wavelength of an absorption line than from this wavelength to other wavelengths. The solar spectrum transmitting atmosphere is convolved with vibrational Raman scattering coefficient of liquid water, divided by the original computed spectrum, with a cubic polynomial subtracted off, to create differential water Ring spectrum. This method is suggested in order to obtain an effective differential water Ring coeffient for the DOAS fitting process, which could be used to improve the accuracy of the retrieval of the trace gases concentration. The method does not rely on radiative transfer model of water, which would be time-consuming and depending on lot of parameters. Therefore, it is very fast and convenient.