Monitoring Sea Water Turbidity by means of the Robust Satellite Technique (RST)

Monitoring Suspended Solid Material (SSM) concentration in coastal areas is important because of its impact on water quality, especially in terms of phytoplankton and benthic algae productivity that decrease as a consequence of the reduction in the photic depth associated to increases of SSM concentrations. Remote sensing techniques have already demonstrated their potential in supporting, at least, traditional in situ methodologies for SSM measurements. Data acquired in the Visible - Near Infrared spectral region (VNIR) of the electromagnetic spectrum have been generally used for this application, exploiting the spectral behaviour of clear/turbid water. One still open challenge is the low sensitivity of these methodologies in shallow waters where discriminating the SSM contribution from the sea bottom one is not trivial. Another problem of EO-based techniques is that, being often calibrated at local scale, their exportability at global scale is generally difficult. In this paper, the Robust Satellite Technique (RST) has been applied for monitoring SSM concentration variations in different Mediterranean coastal areas by using VNIR MODIS data. Thanks to the natural RST independence on the investigated signal as well as on the analyzed area, such a technique can be more easily exported at a global scale than other traditional EO methods. In addition, being a differential approach, RST automatically allows us to discriminate just the contribution of reflectance due to the sea bottom, previously characterized through the multi-temporal analysis, providing a reliable detection of SSM variation. In this paper, some RST-based SSM products developed in the framework of the projects IOSMOS (IOnian Sea water quality MOnitoring by Satellite data, OP ERDF Basilicata), MOMEDAS (MOnitoraggio delle acque del mar MEditerraneo mediante DAti Satellitari, OP Basilicata SRF) and RITMARE (La Ricerca Italiana per il Mare, CNR-MIUR), will be described.