SAN FRANCISCO -- Ohio State University researchers have demonstrated that a satellite radar system can be used to gauge water levels in vegetated wetlands.
C.K. Shum, professor of earth sciences at Ohio State, and his colleagues hope to develop the technique to aid studies of wetland hydrology -- including the role that wetlands play in quelling storm surges caused by large hurricanes.
They examined data from the TOPEX/Poseidon satellite, taken from four selected sites around Louisiana from 1992-2002. Using an innovative data processing technique, called "retracking," they were able to remove signal errors such as those caused by wetland vegetation.
TOPEX/Poseidon measures the altitude of objects with radar. Since 1992, the joint mission of NASA and the French Space Agency has used this technology, called altimetry, to measure global sea height.
In the Ohio State study, the radar altimeter signal showed that water levels were rising in some Louisiana wetlands and dropping in others -- results which agreed with available water-level gauges on the ground.
Graduate student Hyongki Lee developed the technique to chart how the wetland water level changed over the ten years. He presented the results in a poster session Tuesday, December 12, 2006 at the American Geophysical Union annual meeting in San Francisco.
This preliminary study doesn't say much about the general state of the Louisiana wetlands, but it does reveal water level changes in selected sites over that decade, including changes caused by seasonal rainfall.
"These kinds of observations could one day help quantify the depletion or rise of water level in wetlands. In this first study, we were mainly just trying to show that the technique works," Lee said.
Wetlands pose two challenges to radar altimeter studies, he explained. Wetland plants diffuse the radar signal, while open patches of water are often so calm that their surface
Contact: C.K. Shum
Ohio State University