Retrieval of solar-induced fluorescence spectral shape of oil slicks from the infilling of solar Fraunhofer lines

Abstract

In this paper we present the spectral behavior of the Solar Induced Fluorescence (SIF) of a crude oil, retrieved from its radiance spectrum acquired in eight selected spectral windows of the visible spectrum from about 389 nm to 659 nm. Each spectral window was chosen to cover one or more solar Fraunhofer Lines (FL) so as to retrieve the in-filling due to the oil fluorescence contribution induced by the solar irradiance. The selected Fraunhofer lines were chosen within the solar lines rather than the telluric ones since the former ones offer several advantages for the application from air- or space-borne platform. Solar FL, compared with telluric ones, require a simpler atmospheric model to evaluate ground solar irradiance. Besides, the signal measured at the sensor is not affected by re-absorption effects. For each spectral window, oil fluorescence contribution and reflectance were evaluated by comparing the measured total radiance of the oil with the incident sun irradiance spectrum measured in the same conditions. Fluorescence and reflectance spectral shapes were evaluated within each measured spectral window by applying a spectral fitting method (SFM) and polynomial modeling. Solar-induced fluorescence data were then used to evaluate the fluorescence spectrum of the oil. The SIF spectrum of the same oil was also simulated by using emission-excitation fluorescence data and a simulated solar irradiance. The measured and simulated spectra were then compared.