Remote sensing retrieval of suspended sediment concentration in shallow waters

The dynamics of coastal lagoons and estuarine areas is characterized by a delicate balance between biological and physical processes and the comprehension and monitoring of such processes require observations over a wide range of temporal and spatial scales. Remote sensing techniques in this context are very advantageous and potentially allow overcoming the spatial limitations of traditional in situ point observations, providing new opportunities for a better understanding of the relevant bio-geomorphological processes and for the calibration and validation of spatially-distributed hydrodynamic and transport models. Remote sensing of suspended particulate matter (SPM) concentration in shallow waters must, however, overcome the difficulties associated with i) the influence of bottom reflection, which may interfere with an accurate retrieval; ii) the necessity of accurately knowing the optical properties of the suspended matter, and iii) the importance of providing an assessment of the uncertainty associated with the estimates produced. This work presents a method to estimate SPM concentration in lagoon/estuarine waters by use of a simplified radiative transfer model. We use a calibration/validation method based on cross-validation and bootstrap techniques to provide a statistically sound determination of model parameters and an evaluation of the uncertainty induced by their inaccurate determination as well as by the uncertain knowledge of the bottom sediment reflectance. The method is applied to the Venice lagoon, using observations from a network of turbidity sensors and from several multispectral satellite sensors (LANDSAT, ASTER and ALOS AVNIR). The bootstrap and cross-validation procedures employed show that consistent estimates of SPM concentration can indeed be retrieved from satellite remote sensing, provided that sufficient in situ ancillary information for appropriate calibration is available. The quantification of the estimation uncertainty shows that retrievals obtained from remote sensing are accurate, robust and repeatable. The SPM concentration maps produced show a general coherence with known features in the Venice lagoon and, together with suitable biological information, point to the role played by benthic vegetation in the stabilization of the bottom sediment. © 2010 Elsevier Inc.