|
|
News  Coast-mapping satellites will follow the tides
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, ESA'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.
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.
"We began using radar data from Envisat's predecessor satellites ERS back in the early 1990s to update maps of French Guiana, in co-operation with the French military. Coastal changes occur very rapidly but satellites make possible the easy updating of charts in a way that ships and aircraft cannot."
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).
The coastline is defined as the precise shoreline at the time of high water. This being so, the partner hydrographic organisations are supplying tidal data enabling satellite acquisitions to be planned to coincide with local high tides. For improved accuracy the findings will also be assessed against regional Digital Elevation Models (DEMs) that record topographic relief.
The partner hydrographic organisations will also assist with interpretation and validation of COASTCHART results.
"For example, there is a growing interest in the detailed spatial mapping of coasts as a tool for environmental monitoring and managing marine resources, as shown by Europe fostering a major new strategy on Integrated Coastal Zone Management."
Laurent Louvart of SHOM agreed: "There is a new appreciation of the need to accurately chart the coastal areas as well as inland territories. Environmental emergencies such as the Prestige oil spill in 2002 have underlined this. And with mean sea level rising it is crucial to document the part of the land that will be most affected by this development.
The €1 million COASTCHART project is being managed for ESA by LogicaCMG UK, and takes place as part of the Data User Element of the Earth Observation Envelope Programme. It is due to conclude in late 2006.
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
