AERMAP has been revised (beginning with version 09040) to support processing of terrain

elevations from the National Elevation Dataset (NED) developed by the U.S. Geological Survey

(USGS, 2002). The revised AERMAP program supports the use of NED data in the GeoTIFF

format. AERMAP still supports terrain elevations in the DEM format, and has also been

enhanced to process DEM files of mixed format (e.g., 7.5-minute and 1-degree DEM files) in the

same run. AERMAP currently does not support processing of elevation data in both the DEM

format and the GeoTIFF format for NED data in the same run.

The USGS DEM archives are now static and will not be updated in the future, while the NED

data are being actively supported and checked for quality. Therefore, NED represents a more

up-to-date and improved resource for terrain elevations for use with AERMAP. Due to a

number of problems that have been encountered with DEM data, AERMOD users are

encouraged to transition to the use of NED data as soon as practicable. Problems encountered

with DEM data include incorrect geo-referencing information for entire DEM files and

elevations that reflect the tops of buildings and trees in some cases. The use of NED data should

avoid these issues, and provides additional advantages over the use of DEM data, including the

ability to download a single NED file to cover the entire modeling domain of interest, with a

consistent horizontal resolution and reference datum (generally NAD83). Some applications of

AERMAP using DEM data may involve inconsistent reference datums for adjacent DEM files,

which can result in receptors being located within gaps between files due to the datum shift.

Gaps may also occur within DEM files generated by various software tools to convert from one

format to another when a NAD conversion is involved, e.g., converting1-degree DEM data to the

7.5-minute DEM format to fill areas not covered by available 7.5-minute data. The AERMAP



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