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Feb 2, 2007

Flood Map Modernization Elevations Inadequate; New Map Using Lidar Proposed

The Flood Map Modernization program currently being undertaken by the Federal Emergency Management Agency (FEMA) has inadequate elevation information to map the shape of the land surface in three dimensions, a committee of the National Research Council reported. Such information is critical in determining the likely direction, velocity, and depth of flood flows. The committee found that most of the publicly available elevation data for the U.S. is more than 35 years old.

The committee called for a new elevation mapping program, which it named Elevation for the Nation. This new mapping program should employ light detection and ranging (Lidar) to acquire elevation data it was recommended. Lidar projects short laser pulses of light from a low-flying aircraft and measures the time it takes for the light to bounce back from the surface. The committee found that Lidar is the only technology to produce elevation data accurate enough to meet FEMA's elevation accuracy requirements.

Congress requested the report because of concerns that underlying base map information currently available for much of the nation is not adequate to support the new digital maps being prepared by FEMA. The committee's report found that there is sufficient two-dimensional imagery available from digital "orthophotos" -- aerial and satellite photographs -- to meet FEMA's standards for mapping landmarks such as streams, roads, and buildings that show the context necessary for mapping flood hazard areas.

While the costs for the Lidar mapping program would be significant, the report emphasized that a seamless nationwide elevation dataset would have many applications beyond FEMA's flood insurance maps. The proposed program should first focus on those areas of the country where flood risk to the population justifies collecting new data, the committee said.

You can read the committee's complete report here.

See also: FEMA's Flood Map Modernization Under Fire and FEMA Flood Map Modernization: A Plan For Local GIS Cooperation.

Photo courtesy FEMA.

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