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Because of recurring
flooding, Austin, Texas, needs new flood-hazard rate maps for the
south part of the municipality. The City of Austin asked the Bureau
to collect elevation data over the Williamson and Onion Creek watersheds
using the Bureau's airborne lidar mapping system. Airborne lidar
mapping uses a powerful laser scanning system and Global Positioning
System (GPS) to measure the Earth's topography with great precision
from a fixed- or rotary-winged aircraft.
In May 2002,
researchers, working with the Texas State Aircraft Pooling Board,
collected approximately 260 million lidar measurements over 92 mi2
of the city. Flood-hazard analysis requires an accurate representation
of the ground surface and the stream network free of trees and buildings
and necessitates classification of lidar topographic points. Using
computer algorithms developed by the Center for Space Research,
we identified the Austin lidar data as reflections from the ground,
buildings, or vegetation. Classified lidar data thus provide detailed
information for hydrologic, geologic, and environmental investigations.
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