Study on the Hai-Phong Bay coastal evolution over a sixty year period using remote sensing data

In this present paper, we firstly present the results of the SAR images of ERS-1, ERS-2 and RADARSAT satellites analysis to extract the wave pattern. Such information has been proved to be necessary to explain the beacg-h erosion areas. The second step is to confirm and complete the results derived from a diachronic analysis of aerial photos of 1952 and 1993 completed by SPOT-HRV together with LANDSAT-TM satellite images. The results of this comparison allow (i) the cartography of the erosion and sedimentation areas and (ii) to highlight the relation between these coastal geomorphological processes and the wave patterns. A second cartography of the erosion and sedimentation areas has been established from the comparison of the RADARSAT and the SPOT-HRV images. These data have been used afterwards as a back-image. Over this raster layer, we have superposed a vector layer wich presents the coastal boundaries digitized from the topographic map of 1939 and the aerial photos of 1992. The two coastal lines have been crossed thanks to the ARC/INFO software to obtain a precise estimation of the surface values of the eroded or prograded areas. From this map, it can be concluded that sedimentation mostly occurs along channels and estuaries while erosion areas generally located on the sea front. Coastal erosion processes seem to be driven by the wave and tidal currents in case of storms. In this particular case study, remote sensing data allow the reconstitution of the littoral environment on both long (53 years) and short (4 years) periods of time. This is made possible because the yearly coastal erosion rate can be up to ten meters. It appears that, in this case, the SPOT-XS image is the best choice for the detection of sediment concentration in the estuaries and for the cartography of the coastal evolution. Furthermore, the results are getting better with the ERS-1, ERS-2 and RADARSAT and SPOT-XS data fusion because of the combination of high spectral resolution (SPOT-XS) with a high spatial resolution (ERS-1, ERS-2 and RADARSAT, 12.5 meters).