EARSeL eProceedings Vol. 3, No. 1, 54-68, 2004

Abstract
The study concerns the quantification of suspended sediments in turbid estuarine waters from high spatial resolution remotely sensed data (SPOT-HRV, Landsat-ETM+). It is applied to the following areas: the Gironde and the Loire estuaries (France), where suspended sediment concentrations (SPM) in surface waters vary from 10 to 2000 mg l^-1.
The methodology is essentially empirical. Based on in situ optical measurements, calibration relationships are established between the remote sensing reflectance (R_rs) signal and SPM. These relationships, obtained using reflectance ratios between near-infrared (NIR) and visible (VIS) wavebands, are relatively independent of the sediment grain-size and mineralogy, and of the illumination conditions (e.g. the cloud cover). Consequently, they can be applied to satellite images, even if no simultaneous in situ measurements were carried out concurrently with the satellite overpass.
A bio-optical model is used to explain the obtained empirical results. It relates the inherent and apparent optical properties of the considered estuarine waters. Scattering by sediments is modelled using the Mie theory. Absorption by sediments is modelled according to the existing knowledge in the domain. The modelled optical properties are validated by comparison with in situ measurements.
The established calibration relationships allow an accurate estimation of concentrations, once satellite data are corrected for atmospheric effects. Resulting SPM maps permit to observe the seasonal movements of the maximum turbidity zone (MTZ) and the resuspension phenomena in the Gironde estuary.

ISSN 1729-3782