ENVIRONMENTAL BASELINE MAPPING OF TOTAL SUSPENDED MATTER CONCENTRATIONS IN THE WESTERN SCHELDT ESTUARY SUPPORTED BY THE USE OF SPOT IMAGES

摘要

The construction of a tunnel below the Western Scheldt estuary (Netherlands) and the associated sediment dumping in the estuary may influence the sediment budget and the ecology. For monitoring the effects of the dumping, it is essential to know the baseline situation of sediment distribution and variability. It was decided to use remote sensing as an instrument to provide spatial Total Suspended Matter (TSM) information to support the baseline inventory. Nine selected SPOT images were processed to TSM maps. An optical model was parameterised using in-situ measured inherent optical properties. Simulations with this model were performed with the aim to predict in situ-measured R(0-) spectra. By matching R(0-) simulations to observations, the bac-scattering to scattering ratio and the shape factor could be assessed. Next, the simulation model was used to derive a TSM retrieval algorithm for various SPOT sensors. A sensitivity study was done to examine the robustness of the TSM retrieval algorithm. All SPOT images were corrected for atmospheric influences and for the effects of the air-water interface. A procedure was developed which allows using known reflectance values of dark water bodies to calibrate the atmospherical correction. Some semi-invariant reflectance features were used for extra calibration and validation. As a last step, the atmospherically corrected images were transformed to TSM maps using the TSM retrieval algorithm. All maps were validated using long term averaged TSM measurements and continuous in situ data measurements. The validation proved that the TSM maps correctly described both overall mean concentrations and the local variability.