Wetlands satellite mapping scheme yielding first results

Abundant water makes wetlands the most biologically diverse ecosystems on Earth, more productive even than tropical rainforests. Unlike rainforests, they are scattered across the world, providing regional flood and erosion prevention, water purification and nutrient recycling.

For much of the 20th Century, wetlands were drained or otherwise degraded. However growing understanding of the vital importance of wetlands led to the signing in 1971 of the Ramsar Convention on Wetlands. Today more than 1424 wetlands have been designated as Wetlands of International Importance, a total area of 129 million hectares. The Convention's 145 national signatories commit to maintaining the ecological character and are obliged to reporting on the state of listed wetlands they have designated.

Taking place as part of ESA's Earth Observation Data User Element, the aim of Globwetland is to utilise satellite imagery to provide detailed wide-area views of individual wetlands and their surrounding catchment areas, and how they are changing. This will assist with Ramsar reporting, and also aid national and local conservation efforts – the success of which ultimately comes down to individual wetland managers.

For this reason Globwetland is user-oriented, developing and demonstrating a space-based information service based on the specific requests of local and national users across 50 sites in 21 countries worldwide.

"Our aim is to provide what the wetland managers think is useful," explained Kevin Jones of Vexcel Canada, the company managing Globwetland. "So the first phase was carrying out a detailed survey of user requirements, to know what sites should be acquired, in what style.

"We also need to ensure that products that can be employed locally are also standardised to be of use nationally and internationally.

"Now comes the stage of prototyping products, with specific products being developed based on user requirements. In turn, wetland managers are helping us with ground truthing our products – verifying that what is shown in an image is really there."

Based on the user requirements, Globwetland core products include base maps, land use-land cover (LULC) maps and change detection maps – with historical satellite images being compared with current acquisitions to see what changes have occurred during the last ten years or more. Water cycle regime monitoring maps are also being created using Envisat and Radarsat radar data to show flood and retreat patterns.

Specialised products available if requested include digital elevation models (DEMs) and biophysical data acquired from multispectral satellite sensors, showing vegetation health based on chlorophyll levels or the sediment contents of wetland water bodies.

Cooperation in Canada

Canada's Creston Valley Wildlife Management Area is a Ramsar site in British Columbia, whose management team is working with Globwetland on the developing of prototype products.

Its area manager is Brian Stushnoff, who explains: "The Wildlife Area covers 7 000 hectares. It is a pretty wild area, and there are some difficult and waterlogged parts. What we need is an effective, economic means of knowing how the entire area responds to changing water levels.

"Globwetland has presented our team with a collective opportunity to learn more about satellites, what they can and cannot do. Before the project began, we never realised there were so many different types of data available."

Managing a wetland such as the one in Creston Valley is a complex task. To ensure continued high biodiversity, the water levels of its marshes must be periodically drawn down. Such cycles of wet and dryness mimic nature's droughts, providing oxygen to decompose dead plant material and release nutrients.

In addition, this practice helps stop invasive plant species, such as cattails or reed canary grass, filling open water and pushing out other plants.

"We try to keep up an early stage of succession, and a high level of wetland vegetation can tend to reduce diversity," Stushnoff explained. "We have to rehabilitate areas that get choked with vegetation, drying them up and then ploughing up the ground to get rid of the seed bank that develops over time.

"What satellite multispectral or radar images can do is allow us to map vegetation species, and see where there are concentrations of invasive plants to give us problems. Reed canary grass can stand two to three metres high, so shows up well in a radar image. Radar also shows up the extent of flooded areas well, so we can see how water levels are changing.

"Historical satellite images are useful to see patterns over time – a lot can happen in 30 years, or just a decade. Annual satellite updates will help us into the future."

Classifying wetlands from space

Another advantage of the project is that it should increase our ability to recognise different types of wetlands using Earth Observation, and by extension more accurately classify them within land cover maps.

"Wetlands have been very difficult to identify from space," explained Doug Taylor of Wetlands International, a non-governmental organisation that maintains the Ramsar Sites Database and is a Globwetland partner. "The Millennium Ecosystem Assessment remote sensing group identified this ecosystem as the least well recognised from space.

"Although sensors detecting water are useful, most wetlands are also associated with vegetation, so characteristic wetland surfaces may be anything from forested or floating plants to rice paddies or wet grassland. Building up a catalogue of characteristic signatures for all latitudes has only just started, so the Globwetland project, by virtue of its wide geographical and temporal reach, is a very useful platform."

Globwetland should mean that, for the first time, wetlands should be capable of being recognised solely through Earth Observation imagery.

In preparation, Wetlands International has worked with the European Environment Agency to develop an extension to their Corine Land Cover classification system, developed for the 300-metre-resolution Corine European land cover map derived from satellites. This extension is based on the globally authoritative 'Ramsar Classification for Wetland Type' system, covering all known wetland types.

Kampala COP 9 will present progress

The Ninth Meeting of the Conference to the Parties (COP 9) of the Ramsar Convention is due to take place in Kampala, Uganda from 8 November 2005. The meeting will include a presentation from the Globwetland team on the project's progress so far.

Globwetland involves sites across four continents: North and South America, Europe (including European Russia) and Africa, the countries involved here being Algeria, Egypt, Cameroon, Central African Republic, Chad, Niger, Kenya, Nigeria, Senegal and South Africa.

"This will be an important opportunity to demonstrate the innovative work of the Globwetland project, showing how Earth Observation can be used fruitfully to support wetland managers on the ground in their management planning for Ramsar sites" says Nick Davidson, the Ramsar Convention's Deputy Secretary General. "Many of us recognise the huge potential for satellite-derived information to help,but for the non-expert it's much harder to find out just what Earth Observation tools and sources can help us for each site-specific management issue.

"The experience of the Earth Observation analysts and site managers at these 50 Ramsar sites, many of them in Africa, will help all of us involved in the conservation and wise use of wetlands, wherever we are."

Globwetland partners

Vexcel Canada Inc is leading the Globwetland consortium for ESA's DUE, with subcontractors Remote Sensing Solutions GmbH of Germany and Synoptics Remote Sensing and GIS Applications of the Netherlands. The Netherlands-based Wetlands International organisation is also taking part, both as a sub-contractor and also as a link to the global wetland science community.