The digital sea gauge network of the French Navy's hydrographic and oceanographic service-Reseau d'Observatoires du NIveau de la Mer-RONIM

Since 1992, in order to obtain accurate and high frequency sea level variation data, the French Hydrographic Service, the SHOM, has installed a permanent sea gauge network in co-operation with certain French ports and some other agencies like the French National Geographical Institute (IGN). Today, 8 ports are equipped with the SHOM instrumentation and many other sites will be studied for possible installation. The aim is to have obtained a complete coverage of the ports in metropolitan and overseas France by the year 2003. The accuracy and the permanency of sea level measurements interest the SHOM and its partners for many reasons. The first one is maritime safety (publication of tide tables and maritime charts). This is one of the missions of all the hydrographers around the world and a permanent subject of international co-operation. The SHOM is also a member of the Global Sea Level Observing System (GLOSS) program co-ordinated by the International Oceanographic Commission. The SHOM provides these necessary data to the international scientific community which studies the increase of the mean sea level and climatic changes. The national community is also interested in the statistical studies of the extreme sea levels-the positive and negative surges. These studies are a tool for the coastal and environmental managers who build new piers and ports but this kind of calculation needs long term observation. The technological solution chosen by the SHOM is digital technology linked with ultrasonic sensors. The digital tide gauge is equipped with a modem. The SHOM collects data every week and validates them.