How Earth's land is used

A new global map taken from space is providing scientists with their most detailed picture ever of the Earth's ecosystems and land use patterns.

The data will aid scientists and policy makers involved in land resource management as well as a range of global monitoring objectives such as determining the amount of Carbon released into the atmosphere that could contribute to global warming.

The maps were developed at Boston University, US, using data from the Moderate Resolution Imaging Spectroradiometer (Modis) instrument on Nasa's Terra satellite. The maps are based on data collected between November 2000 and October 2001.

Scientists say the image is an important milestone. "These maps mark a significant step forward in global land cover mapping by providing a clearer, more detailed picture than previously available maps," says Professor Mark Friedl of Boston University.

"With data collected over several years," he adds, "we will be able to create maps that highlight global-scale changes in vegetation and land cover in response to climate change, such as drought.

"We'll also be establishing the timing of seasonal changes in vegetation, defining when important transitions take place, such as the onset of the growing season."

The last global maps of this kind were produced from data collected in 1992 and 1993 by a previous satellite.

Colour coded

Terra was launched on 18 December 1999 and is regarded as the flagship of Nasa's Earth Observing System series of satellites.

The map shows global land cover types in different colours. Each land cover has a different effect on carbon and climate cycles.

There are 17 different land cover types shown in the image, including 11 natural vegetation types such as deciduous and evergreen forests, savannas, and wetlands.

Also show are agricultural land use and land surfaces with little or no plant cover - such as bare ground, urban areas and permanent snow and ice.

"This product will have a major impact on our carbon budget work," says Professor Steve Running of the University of Montana, who uses the land cover maps in conjunction with other weekly observations from Modis.

"With the Modis land cover map we can determine current vegetation in detail for each square kilometre; for example, whether there is mature vegetation, clear cutting, a new fire scar, or agricultural crops.

"This means we can produce annual estimates of net change in vegetation cover. This gets us one step closer to a global picture of carbon sources and sinks."