Initial Publication Date: March 20, 2010

Week 6: Following Rivers Through Time

In 2005, Hurricanes Katrina and Rita ravaged the Gulf Coast. Levees meant to keep the water of Lake Pontchartrain at bay were breached, and massive flooding overtook the city of New Orleans. Scientists now believe that these artificial barriers aren't just failing during major storm events, but are continually weakening the city's natural defenses against flooding. The 350 miles of levees "protecting" New Orleans prevent new sediment from building up in the Mississippi River delta. Without fresh sediment to offset natural subsidence of the land, Louisiana is sinking even further below sea level and losing precious wetlands that buffer the land from storms and serve as important wildlife habitat and nursery grounds. The Louisiana delta is currently sinking 5-10 millimeters and losing 16,000 acres of wetlands every year.

Dr. Zhong Lu, USGS physical scientist.

Zhong Lu is a physical scientist with the USGS Earth Resources Observation and Science (EROS) Center and the Cascades Volcano Observatory (CVO). Dr. Lu specializes in a remote sensing technique called satellite-based Interferometric Synthetic Aperture Radar (InSAR). For most of his career, Dr. Lu has applied this technique to the study of volcano deformation mapping. However, after learning that a hydrology expert had demonstrated that radar waves could bounce off water beneath the thick canopy of the Amazon, Dr. Lu wondered if he could also use the technique to make a map of how land was sinking in and around New Orleans.

Using vegetation maps and RADARSAT-1 Synthetic Aperture Radar (SAR) data distributed by the NASA Alaska Satellite Facility Distributed Active Archive Center (DAAC), Dr. Lu and his colleage Oh-Ig Kwoun generated InSAR images of Southeastern Louisiana wetland vegetation with unprecedented vertical accuracy. Dr. Lu's use of satellite technology to detect and monitor water-level changes in wetlands allows scientists to make measurements over wider areas and at more frequent time intervals. These measurements are crucial for flood hazard modeling, wetland ecology and management, and to create long-term records that will help us understand how swamp forests can regenerate under changing conditions. More importantly for Louisiana, these measurements can help experts identify ways to counteract land subsidence and wetland loss.