Measurements of satellite signals bouncing off a calm mountain lake may pave the way for a fleet of spaceborne sensors or groups of seaside towers that can quickly and inexpensively monitor local or global changes in sea level.
Central Oregon's scenic Crater Lake, one of America's deepest bodies of water, sits within the caldera left behind by an ancient volcanic eruption. From an observation point on the edge of the ancient crater and 480 meters above the lake, scientists recorded the signals coming straight from Earth-orbiting Global Positioning System (GPS) satellites, as well as the signals bouncing off the water's surface.
By measuring the slight delay between the direct and the reflected signals, the researchers could calculate the height of their observation point above the smooth lake to within 2 centimeters, says Robert N. Treuhaft, a physicist at NASA's Jet Propulsion Laboratory in Pasadena, Calif. Treuhaft and his colleagues report their field experiments in the Dec. 1 2001 GEOPHYSICAL RESEARCH LETTERS.
If scientists can develop similar methods …