Context and objectives
The main objective of the study consists to the process of radar images from ERS-1, ERS-2 and the Canadian satellite RADARSAT, in order to extract the swell plan and to study their anomalies. This information is necessary to explain the localisation of the eroded areas on the coastal zone. The radar images must also be used to validate the swell simulation model by comparison with the swell plan extracted from the radar images.
The second objective consists to complete the results obtained during the multitemporal comparison between the aerial photographs of 1952 and of 1993, by using the SPOT XS images and LANDSAT TM images. The documents will allow mapping the areas of erosion and the areas of sedimentation and to establish a relation with the swell plan obtain by simulation. A comparison with the tide currents will be also realised.
Expected scientific results
The first objective has not been reached, because no radar image were acquired during the specific meteo-marine conditions allowing the location of the swell plan. Only the radar image acquired on 04/06/1997 shows a front-line between two water bodies, that has different physical and chemical patterns. Therefore, the simulation model has not been validated during this study.
The map of erosion and sedimentation areas was carried out from the RADARSAT image acquired on 15/12/1996 and from the SPOT XS image acquired on 31/08/1992. This colour composition is used as the background of the map. Over this raster layer, we have put a vector layer that represents the coastline in 1939 (extracted from a topographical map) and the one in 1992 (extracted from aerial photos). Both coastline were crossed using the ArcInfo GIS software, in order to obtained the surface value for eroded and sediment areas.
The map of the areas of sedimentation and erosion shows that the sedimentation is often located along the channels and along the rivers. The areas of erosion are located on the coastal line. The phenomena of erosion seem to be due to the effects of the tide currents and to the swell that occur during very strong tempests. Most frequent swells, that occur during the standard meteorological conditions, breaks before to reach the coast-line and, therefore, has almost no influence on the coastal zone evolution.
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