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Contribution of SAR (RADARSAT) and AVNIR (ADEOS) images to the study of bathymetry and wave field in the Bay of Hai Phong (Vietnam)
www.belspo.be/belspo/fedra/proj.asp?l=en&cod=t4/dd/18#descr

More:  Institutes 
Dutch title: Bijdrage van SAR (RADARSAT) en AVNIR (ADEOS) beelden tot de studie van de bathymetrie en het golfvlak in de Baai van Hai Phong (Vietnam)
Parent project: Research action SPSD-I: Sustainable management of the North Sea, more
Reference no: T4/DD/18
Period: March 1997 till November 1997
Status: Completed

Institutes (2)  Top 
  • Belgian Science Policy (BELSPO), more, sponsor
  • Université de Liège; Laboratoire de Géomorphologie et Télédétection (Ulg/GEOMO), more

Abstract:
  • 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.

  • Methods :

    1. Geometrical correction of each satellite image and of the aerial photos in UTM co-ordinates in order to carry out the overlay map.
    2. Speckle suppression of the radar images with a median filter 5X5.
    3. Directional filters to extracted the linear structures at the sea surface (swell).
    4. Overlay between each image and the bathymetry measured in situ.
    5. DTM realised with Arcinfo in order to realise the swell simulation model.
    6. Mapping of the areas of sedimentation and erosion by overlaying the different images (multitemporal study). Overlaying of RADARSAT (15/12/1996) and SPOT XS (31/08/1992) images overlaid with the coast-lines in 1939 and in 1992.

  • 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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