Satellite image acquisitions will be synchronised with the tides as part of an ambitious new project to map coastlines from space.
Formally beginning in September, European Space Agency’s COASTCHART project aims to develop and qualify a specialised coastline information system that provides satellite-derived coastal data products suitable for operational use by hydrographic organisations.
Accurate up-to-date marine charts are essential for safe shipping navigation. They also increasingly serve as management tools for coastal zones — areas that are economically and environmentally important as sites of harbours, fisheries, oil and gas fields, tourism sites, wildlife habitats and home to the majority of the human race.
National hydrographic organisations, as co-ordinated by the International Hydrographic Organisation (IHO), have the global task of mapping the sea and also the ‘littoral’ – that is, the stretch of shore affected by the sea. Their work is based on surveying campaigns using ships and air-based platforms Updates may also be provided by shore-based authorities or those working in the near shore waters.
However the world has around 860000 km of total coastline, and coasts are always changing: sand and mud banks have been known to shift hundreds of metres during a single year. Aerial surveying can cover hundreds of kilometres in a day, but is costly and can only be performed if weather conditions are right. Both tropical and polar coasts may stay enshrouded in cloud and precipitation for weeks or months at a time.
Radar sensors such as the Advanced Synthetic Aperture Radar (ASAR) aboard ESA’s Envisat can penetrate cloud cover as well as local darkness. They work on the basis of detecting reflected radar pulses to measure surface roughness.
To qualify the COASTCHART system the plan is to map 6000 km of West African coastline covering 15 countries extending from Senegal to the Republic of Congo. ESA is partnering with European hydrographic organisations working in the region: Spain’s Instituto Hidrográfico de la Marina(IHM), Portugal’s Instituto Hidrográfico (IHPT), France’s Service Hydrographique et Océanographique de la Marine (SHOM) and the United Kingdom Hydrographic Office (UKHO).
Paper and digital map products of the entire coastline will be delivered to a scale of 1: 50000, with 14 key sites including harbours, maritime facilities and river approaches to be delivered to a very-high-resolution 1:15000 scale. The project is making use of Envisat ASAR imagery, together with SPOT 5 optical imagery for precision mapping.