REMOTE SENSING OF TURBID WATERS: A CLOSER LOOK AT THE SWIR

KNAEPS, E.; RUDDICK, K.; DOGLIOTTI, A. I.; DOXARAN, D.; STERCKX, S.

Conferencia; Ocean Optics XXI; 2012

In recent years there is a clear increase of interest in the Short Wave Infrared (SWIR: 1-3µm) for both turbid water atmospheric correction and the retrieval of Total Suspended Matter (TSM). This has led to the inclusion of longer wavelength bands in new ocean colour instruments such as the Ocean and Land Color Instrument (OLCI) on Sentinel 3. However a sound theoretical basis was missing and there were no in-situ observations of the marine reflectance in the SWIR due to thelack of suitable instrumentation.Based on the high absorption of pure water in this spectral region and the lower contribution of ocean substances compared to Visible and Near-InfraRed (VNIR) wavelengths, the water reflectance in the SWIR was generally assumed to be zero, even for highly turbid waters. The only assessments of this assumption are image based. For instance, Wang et al. (2009) assessed the black pixel assumption for the extremely turbid China east coastal and the highly turbid La Plata Estuary regions for the MODIS SWIR bands. Only very recently (Knaeps et al., 2012) water leaving reflectance measurements in the SWIR were presented for the Scheldt river and related to the TSM concentration indicating the limits of this SWIR black pixel assumption and indicating the potential of this spectral region for TSM retrieval. Now also a sound theoretical basis is presented for the SWIR marine reflectance and new field measurements are presented to determine the variability of the water reflectance in the SWIR.