Operational coastal map re-actualization by RADAR SAR images, examples in French Guiana, Mauritania and Cameroon

The French Hydrographic Office has to publish information for navigation security in its responsible zones (French territories, West African coasts (with agreements between these countries and France), Djibouti, Viet-Nam, etc.). Nautical charts on African coasts are old and had often been established in the 1950s. Local geodetic reference systems used are not well known, so maps are not in accordance with GPS navigation. In French Guiana, coastal evolution is so important that nautical charts are obsolete. Sedimentation and erosion of mangrovia vegetation can reach one kilometre per year. We study the contribution of RADAR SAR imagery for nautical chart updates. Our interests are coastline, interidal zone delimitation, harbour structures and bathymetry (<20 metres). We present solutions for different problems. First, for cartographic applications, we reference geographically our ERS images in a global geodetic reference system without ground points, we use precise orbitographic products, differences between geoid and global ellipsoid and ERS annotation files: precision estimation of this step was made by GPS measurements and also comparison between images acquired in ascending and descending mode. Second, ground interpretations permit first in Mauritania and French Guiana to follow coastal evolution and particularly coastline erosion and flood risk zones, and last in Cameroon to understand high and low vegetation distribution in mangrovia and in Wouri estuary, to follow sand banks which obstruct the Douala city channel. We propose a methodology for ERS RADAR SAR use including interferometry, the speckle reduction process and automatic detection tools. Third, we present new coastal cartographic documents for regions with strong changes and a low map update frequency