Context and objectives
This study focuses on the detection of sediment plumes and sediment contents brought down by large rivers. The knowledge of the main currents and the amount of sediment is important with regard to the development of deltas and consequently with regard to the navigableness of the rivers. The condition of sediment plumes is traditionally examined through direct measurements from a ship. These observations are point tied along the ship's course. This traditional approach doesn't offer a survey of the total condition of the sediment plumes. To come to such an overall picture the observation grid has to be refined in the conventional way, implying that the costs will sharply increase. Due to the synoptic capacity, the use of remote sensing documents could offer a solution. However the question rises to what extent these data can be used to determine the sediment contents and sediment plumes. This question is asked by the companies HAECON N.V. and DEME N.V./Dredging International, for the case of the outlet of the Rio de la Plata (Argentina and Uruguay). Both companies are co-operating to elaborate a project of dredging-works to keep the ship's course in the Rio de la Plata open and to control the influence of the dredging-operations on the environment.
With regard to the theme of this research satellite images with information on the visual reflected light will be needed. This study aims a multiscale approach :
- First of all a detailed interpretation has to be set up by means of relatively fine resolution images; this interpretation is a tool for the following up of the dredging-works in the channel. For that it is necessary to correlate the field data with the digital values of the visual bands of the Landsat TM images. This will be done in two periods: one during high discharge of the Rio de la Plata, another during low discharge. The compiled correlations allow to carry out the image classification for both periods. As the branches of the Rio de la Plata reach a maximum depth of about 9-m, the digitised bathymetrical maps will be used to improve the image classification processes.
- A second approach is situated on a ?regional? level and will happen by means of medium resolution images (Resurs-01) in order to study the environmental effects of dredging-works on the different water catchments at the Rio de la Plata. To obtain an interpretation of the Resurs-01 image a correlation between the Resurs-01 bands and the similar bands of the Landsat TM will be compiled.
- A third approach is situated on a ?global? level and wants to observe the course of the sediment plumes in the Atlantic Ocean. For that purpose rough resolution images of the SeaWifs sensor will be used. A comparison will be made between former achieved results and the SeaWifs images.
In a last step an error analysis will be made showing to what extent the satellite images and the proposed method give an accurate view on the situation of the suspension material in the Rio de la Plata. At the same time an analysis will be made of costs and benefits comparing the conventional field measure methods and the use of remote sensing methods.
Expected scientific results
1. Digital Elevation Models for the Rio de la Plata and adjoining part of the Atlantic Ocean and for a detailed part (LANDSAT 7 ETM+ scene) of the Rio de la Plata (resolution: 30m)
2. Color composites of the LANDSAT 7 ETM+ and SeaWIFS data
3. Classification of the LANDSAT 7 ETM+ image based on 'Density Slicing' indication the sediment plumes
Based on these results it can be concluded that it is possible to detect patterns of sediment transport in large delta systems used remote sensing techniques. The LANDSAT 7 ETM+ sensor can be used to make a detailed study, while the SeaWIFS gives the opportunity to have a synoptic view of the Rio de la Plata and adjoining part of the Atlantic Ocean. Also a model can be developed to detect the 'cross points' of the sediment plumes over the man-made channels. This model can be used to optimize the dredging activities.
Deliverables: Digital Elevation Model of the Rio de la Plata, classified image based on relative sediment loads, 3D views