Interagency project measures impact of Hurricane Bonnie
- By L. Scott Tillett, L. Scott Tillett, Margret Johnston
- Sep 13, 1998
Three federal agencies are collaborating on a coastline mapping project used this month to help determine Hurricane Bonnie's impact on North Carolina's dunes and other coastal structures.
NASA, the National Ocean-ic and Atmospheric Administration and the U.S. Geological Survey have teamed up to collect and proc-ess data, which is used to create detailed maps and cross-sectional diagrams of the coastline. State and local land managers use the material to decide zoning issues and determine the location and extent of dredging projects.
NASA and NOAA scientists collected data from the coasts of Virginia, North Carolina and South Carolina during the first week of September. They will turn the data over to USGS coastal geologists, who will conduct ground surveys of impacted areas to verify the data. The scientists will compare this data with existing topographical maps to assess any changes brought about by the storm.
The NASA Wallops Flight Facility, Wallops Island, Va., originally developed the laser beach-mapping technology to monitor changes in the polar ice caps, said Bill Krabill, NASA's project scientist for arctic ice mapping in Greenland. The laser can map in a week what would take months to map using traditional surveying methods, he said.
The 6-year-old polar ice cap mapping project uses NASA's Airborne Topographic Mapper, which is a laser altimeter that sends out a beam over a 300-kilometer swath of beach from a NOAA aircraft flying at about 109 mph.
This beam hits a target on the surface and bounces some of the energy back to the plane, Krabill said. The laser system scans and collects 5,000 samples per second. "We produce incredibly dense measurements of the topography as we fly along," he said.
Laser Altimeter Meets GPS
The laser altimeter system is precise enough to detect a formation as small as a basketball, Krabill said. It works by measuring the time it takes the pulse of energy to bounce back, determining the distance— within 2 inches— between the beach and the plane.
But scientists still need to know the exact location of the plane to correlate that data. That is where the Global Positioning System comes in, Krabill said. GPS receivers, one on the plane and one on the ground, tell the scientists the location of the aircraft within 2 inches, he said.
Once collected, the data makes its way into the hands of NOAA technicians such as Mike Hearne, a contractor who works as a spatial data specialist for NOAA. Hearne uses the data to produce digital contour maps on CD-ROMs that coastal managers at state and local agencies can use to assess damage to fragile dunes and to see how well dune rebuilding or "renourishment" projects fared.
"We're interested in whoever is interested in beaches at the state and local level," Hearne said. Coastal managers want the data to determine where government agencies can issue building permits or to determine where dune renourishment is needed, Hearne said.
Hearne said NOAA hopes to provide coastal managers with the data in a form that is more interactive than a contour map on a CD-ROM. NOAA officials envision providing data that can be plugged into a geographic information system (GIS), allowing managers to conduct more detailed planning and assessment of coastal erosion or buildup.
"We would like to have the data available to them either on CD-ROMs or even over the Web...in something they can bring into a GIS package," Hearne said.
For now, beach mapping is the fastest and least expensive way to measure shoreline changes after a storm, and the technology could be used to validate the data that ultimately will be collected by a laser altimeter on a satellite, Krabill said.
The beach measurement project also is giving NASA a jump on plans to launch a laser altimeter on a satellite in 2001, he added.
Other laser beach-mapping studies include mapping the coast of the Delmarva Peninsula, which stretches from Delaware to Virginia, and the coasts of California, Oregon and Washington state, where scientists are documenting changes caused by the El Nino weather phenomenon.