Coast-mapping satellites will follow the tides

Sep 23, 2004
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.

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.

"The textures of land and sea surfaces are quite different, so radar imagery shows up coastlines very well in most cases," said Professor Jean-Paul Rudant of the Université de Marne La Vallée in Paris, a pioneer of the use of radar imagery for coastal mapping and scientific advisor to the COASTCHART project.

"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 makes 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).

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.

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.

"Participating in COASTCHART is a means of testing how well Earth Observation can meet our needs in delivering charting in this area," said John Pepper of UKHO. "Potentially space represents an extra source of information in areas where reliable and up-to-date information is at a premium. By capturing coastal information, we will better be able to deliver solutions to users both on shore as well as at sea."

"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.

"Earth Observation promises to be a cost-effective way of maintaining our charts, although it will supplement ground-based surveying, not replace it. The need for people on the ground is always there, because it is very difficult to interpret imagery without a ground presence."

The ˆ1 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.

Source: ESA

Explore further: Computer model shows moon's core surrounded by liquid and it's caused by Earth's gravity

add to favorites email to friend print save as pdf

Related Stories

Physicists discuss quantum pigeonhole principle

11 hours ago

The pigeonhole principle: "If you put three pigeons in two pigeonholes at least two of the pigeons end up in the same hole." So where's the argument? Physicists say there is an important argument. While the ...

Giant crater in Russia's far north sparks mystery

13 hours ago

A vast crater discovered in a remote region of Siberia known to locals as "the end of the world" is causing a sensation in Russia, with a group of scientists being sent to investigate.

NASA Mars spacecraft prepare for close comet flyby

14 hours ago

NASA is taking steps to protect its Mars orbiters, while preserving opportunities to gather valuable scientific data, as Comet C/2013 A1 Siding Spring heads toward a close flyby of Mars on Oct. 19.

Recommended for you

Comet Jacques makes a 'questionable' appearance

12 hours ago

What an awesome photo! Italian amateur astronomer Rolando Ligustri nailed it earlier today using a remote telescope in New Mexico and wide-field 4-inch (106 mm) refractor. Currently the brightest comet in ...

Image: Our flocculent neighbour, the spiral galaxy M33

12 hours ago

The spiral galaxy M33, also known as the Triangulum Galaxy, is one of our closest cosmic neighbours, just three million light-years away. Home to some forty billion stars, it is the third largest in the ...

Titan offers clues to atmospheres of hazy planets

12 hours ago

When hazy planets pass across the face of their star, a curious thing happens. Astronomers are not able to see any changes in the range of light coming from the star and planet system.

Having fun with the equation of time

12 hours ago

If you're like us, you might've looked at a globe of the Earth in elementary school long before the days of Google Earth and wondered just what that strange looking figure eight thing on its side was.

User comments : 0