Monitoring Earth's Vital Signs; April 2000; Scientific American Magazine; by King, Herring; 6 Page(s)

Flying 705 kilometers above the earth's surface, a satellite called Terra is conducting a comprehensive health examination of our world. Everything from clouds and plants to sunlight and temperature and fire and ice influences climate, and Terra is just beginning to collect this information every day over the entire earth. As the bus-size satellite circles the globe from pole to pole, its sensitive instruments track the planet's vital signs as each region comes into view.

Certain environmental changes are occurring today at rates never seen in our planet's recent history. Imagine, for instance, the hundreds of fires set deliberately every year to clear land for agriculture, a practice that has quadrupled during the past century. Humans today burn an average of 142,000 square kilometers of tropical forests-an area roughly the size of Arkansas-every year. Some of Terra's sensors can track the flames and gauge their intensity, whereas others measure the extent of burn scars and observe how smoke particles and gases move through the atmosphere. One of these sensors can even distinguish changes at a resolution of 15 meters-a view close enough to pick out spots where smoldering embers may again burst into flame.