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GCN : April 2014
CASE STUDY GEOSPATIAL GAME CHANGER Big storms have a way of exposing poor planning and outdated technolo- gies. The Federal Emergency Management Agency took a lot of heat for its response to Hurricane Katrina in 2005. And when Hur- ricane Sandy struck major parts of New York and New Jersey in October 2012, many buildings that were not in flood-prone ar- eas -- at least according to FEMA s Flood Risk Information Maps -- were swamped. FEMA shouldn t be blamed too quickly for the inaccuracy of its flood-risk maps, however. While there have recently been revolu- tionary improvements in the ac- curacy of flood maps and in the predictive power of hydrologic modeling, by 2012 only a fraction of the country had been mapped using the newer technologies. "The biggest change in the ac- curacy of flood zones and flood hazard maps in general is due to LiDAR," said Marie Peppler, flood and hazards program coordina- tor at the U.S. Geological Survey. LiDAR (light detection and ranging) devices emit laser puls- es and measure the time required for the pulse to reflect back to the device. According to Mark DeMulder, chief of USGS s Na- tional Geospatial Program, cur- rent LiDAR equipment deployed on aircraft by USGS contractors can measure the elevation of the underlying terrain within 9.25 centimeters. Prior to LiDAR -- from the early 1900s to the early 21st century -- most elevation maps were creat- ed using manual surveying meth- ods. The old contour maps have a margin of error in elevation accuracy as high as plus or minus 20 feet. "So we re going from plus or minus 20 feet to 9.25 centime- ters," DeMulder said. And when it comes determin- ing flood risk, elevation mea- surements are the most critical factor, according to Peppler. "The accuracy of the map is 110 percent dependent on the accu- racy of your elevation data," she said. "As we get better elevation data sets we can do better mod- eling on top of that." Elevation mapping, of course, is useful for many other purpos- es besides assessing flood risk. Among other things, LiDAR data can be used to monitor the health of crops, to detect archeological artifacts, to measure the biomass of forests and to perform mineral exploration. As a result, a group of fed- eral agencies -- including USGS, the National Oceanic and At- mospheric Administration and NASA -- work in close concert to manage collection of LiDAR data. In fact, most of the actual collection of LiDAR data is per- formed by contractors. "We con- tract with the private sector for acquisition of the data," DeMul- der said. "One of the advantages of operating that way is that the capital investment in equipment and refresh of technology hap- There have been revolutionary improvements in the accuracy of flood maps, but only a fraction of the country has been mapped using newer LiDAR technologies Flood planners await next-gen laser mapping BY PATRICK MARSHALL 28 GCN APRIL 2014 • GCN.COM "The biggest change in the accuracy of flood zones and flood hazard maps in general is due to LiDAR." -- MARIE PEPPLER, U.S. GEOLOGICAL SURVEY