Projet de recherche S0/67/036 (Action de recherche S0)
Context and objectives
To assure the accessibility of ports, shipping channels must be dredged regularly to maintain an adequate water depth. Dredging operations are subjected to strong environmental regulations which require that the sediment dynamics are monitored, temporally as well as spatially, in an ever increasing manner. IMDC, the private partner in this project, prepares specifications and recommendations of techniques, equipment and methods for any dredging project. IMDC requires information on the spatial variation of turbidity for e.g. the optimization of the dredging locations to minimize the recirculation of sediments towards harbors after dumping.
To support IMDC in their activities, a service is developed in the ORMES project which provides suspended sediment maps from remote sensing images in an efficient way.
This project aims: (1) to develop a simple and robust procedure for near surface (or 2 D) sediment concentration mapping from remote sensing data (2) to operationalise and automate the procedure and (3) to implement the procedure/software at the private partner.
Methodology
In the ORMES project the Scheldt Estuary has been chosen as main study site mainly because of its dynamic complexity. A large dataset consisting of a series of airborne hyperspectral images was obtained at different stages of the tidal cycle. Simultaneously with the airborne campaign a field survey took place. Using these field data and the high resolution airborne data, a reliable semi-empirical algorithm has been developed to derive near-surface suspended matter maps in an operational way. The produced TSM maps were in very good agreement with known variations of the suspended sediment content over the tidal cycle. The ORMES project focused mainly on the full capability of state-of-the-art airborne hyperspectral sensors, with some minor tasks devoted to satellite based TSM derivations. The final product of the ORMES project is a user-friendly software for the production of suspended matter maps.
This software will be implemented at IMDC and TSM concentration maps can be generated from remote sensing data with a limited number of water samples for calibration.
Results
The following results have been obtained :
We have had a very successful field and airborne campaign. On the basis of this campaign a large database has been generated which contains
- hyperspectral data cubes at different processing levels (radiometrically, atmospherically and geometrically calibrated) covering several stages in tidal cycle.
- turbidity data measured almost continuously during the campaign
- in-situ spectral reflectance measurements
- specific inherent optical properties (backscattering and absorption spectra)
- suspended sediment concentration of a large number of water samples
- chlorophyll content of several water samples
A reliable semi-empirical algorithm, based on a band difference term log-linear regressed against suspended sediment concentration, has been developed to generate suspended sediment maps from airborne hyperspectral data.
The suspended sediment maps produced describe well the known variation of sediment behaviour in the Lower Sea Scheldt area and contribute to the improvement of our knowledge of spatial and temporal sediment distribution in this complex river system. The suspended sediment maps also agreed well with sediment transport model simulations and cross-section turbidity measurements.
A user friendly software has been developed (see next point description of the end product)
Products and services
User-friendly software for the production of suspended matter maps has been written. The user can interact with the software by a self-evident graphical user interface. A manual describing input, output and operation is also delivered. The software will be implemented at the private partner’s and personnel will be trained.
