Turbidity analysis in Sicilian coastal zones by means of remote sensing images and spectroradiometric measurements

Abstract

Water turbidity has a wide range of variability both spatially and temporally. Rivers transport sediments to the river mouth following a seasonal behaviour and occasionally during flood events (Doxaran et al., 2006; Pribble et al., 2001). Once in the sea, sediments are spatially driven by currents, and re-suspended by waves from the bottom, changing water turbidity in the tidal and sub-tidal zones (Cloern et al., 1989; Uncles et al., 2002; Wolanski & Spagnol, 2003). Moreover human activities such as transport and dredging occasionally and locally influence turbidity magnitude and distribution (Schoellhamer, 1996). In recent years the pollution of the maritime environment suggests that only operational monitoring activities can improve the preservation of this vulnerable and valuable ecosystem. Furthermore, these practices can aid the understanding of the anthropic impact on the maritime ecosystem. Within this framework, monitoring the spatial-temporal distribution of coastal water quality parameters plays a fundamental role. To this aim remote sensing techniques represent a suitable tool for water quality assessment, and for continuous monitoring of the Sicilian coastal waters. A chain of automatic processes has been developed in order to assess the Nephelometric Turbidity (NT). An algorithm has be calibrated using in situ data, obtained by intensive field campaigns undertaken in the three Sicilian gulfs (Castellammare, Augusta and Gela gulfs) during three periods in 2008 (at the beginning of July, August and September for each gulf).