Measuring earth from outer space.

Radio astronomers have constructed detailed profiles of the atmospheres of five planets in the solar system, mapping temperature, density, and pressure at various elevations. None of the five is Earth. Now, a team of Stanford University and Lockheed scientists proposes adapting one of the methods they've perfected on Venus and Jupiter - radio occultation - in which radio waves, beamed from a spacecraft, travel through a planet's atmosphere, bending and changing speed, and thus revealing details about the Earth's composition. The technique would provide the first systematic, global view of atmospheric conditions at many altitudes - data even weather satellites can not supply.

Such studies of Earth have been prohibitively expensive because they required radio signals to be sent and received from outside the planet's atmosphere. The method is economically feasible for the first time because the U.S. military's NAVSTAR Global Positioning System (GPS) is fully operational and available for industry and research use. The 16 GPS satellites...