Unfinished Business: Shuttle to Chart Earth's Environment

SIX astronauts are ready to take the space shuttle Endeavour into orbit on Thursday to complete an environmental survey the spacecraft began last April. That's when Endeavour first carried the Space Radar Laboratory - the most advanced imaging radar yet sent into space for civilian purposes.

It charted 44 million square miles of widely varied terrain in 44 countries during the Northern Hemisphere spring and the Southern Hemisphere fall. Now the radar lab is to cover much of the same area on a 10-day mission. A group of international scientists want to chart the changes that have come with the Northern Hemisphere summer and Southern Hemisphere winter.

The $366-million radar is a joint product of the German and Italian space agencies and the United States National Aeronautics and Space Administration (NASA). Unhindered by clouds or fog, the radar can map areas even when other satellites cannot ``see'' them. It can often see beneath dry snow and sand, revealing buried ancient river beds or archaeological sites, and it can distinguish desert from jungle, wetlands from savannas.

Taken at different times over many years, the charts can show how environments are changing and how different factors in an environment work together. Often, this may be the only way to get such an overview in inaccessible regions. This is especially useful for assessing the health of the habitat of endangered wildlife, such as gorillas in war-torn Rwanda or pandas in remote parts of China.

Eventually similar equipment may be orbited permanently on unmanned satellites to continuously monitor Earth.

Once again, Endeavour's astronauts will also be tracking an environmental factor the radar cannot see - carbon monoxide (CO) gas. This is a major pollutant produced by cars, coal-burning furnaces, and the burning of vegetation. Locating its sources, tracing its spread or reduction, and monitoring its destruction helps scientists understand how well the atmosphere is cleaning itself of manmade pollution.

Earlier surveys had shown more CO concentration over the tropics and Southern Hemisphere than over the Northern Hemisphere generally. They also identified biomass burning in Africa and South America as major sources. Endeavour's April survey surprised scientists by showing relatively high CO concentrations over the Northern Hemisphere.