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U.S. Geological Survey Open-File Report 2011-1127

Construction of a 3-Arcsecond Digital Elevation Model for the Gulf of Maine

National Elevation Data

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National Elevation Data

Figure 13. Map showing the extent of data for the Gulf of Maine from the National Elevation Dataset of the U.S. Geological Survey.

The 1-arcsecond resolution (approximately 30-m) National Elevation Dataset (NED) is a raster product assembled by the U.S. Geological Survey (USGS) (fig. 13). The NED is designed to provide national elevation data in a seamless form with a consistent datum, elevation unit, and projection. Data corrections are made in the NED assembly process to minimize, but not eliminate, artifacts, perform edge matching, and fill sliver areas of missing data.

Data Properties:
  • Vertical Datum:  NAVD88
  • Vertical Accuracy:  Unknown
  • Coordinate System:  Geographic decimal degrees
  • Horizontal Datum:  NAD83
  • Horizontal Accuracy:  Unknown
  • Resolution:  1 arc second (approximately 30 m)
  • Year Data Collected :  1999
  • Format:  ESRI Arc Grid
  • Date Data Downloaded:   October 2009
The first step in processing the data was to convert the files from the ESRI binary grid format to ASCII XYZ format. ESRI grid data were read and converted to GMT .grd format to using the GDAL 'gdal_translate' tool and the GMT 'grd2xyz' tool.

The GMT 'blockmedian' command was used to resample the data from 1-arcsecond (approximately 30 m) to 3-arcseconds (approximately 90 m).

The final processing step was to clean the data by removing any points that fell offshore from the coast. The ArcMap 9.2 ArcToolbox Analysis 'near' tool was used to clip all the data lying within the "Medium Resolution Digital Vector U.S. Shoreline" shapefile for the contiguous United States and save the points lying within the boundaries of the shapefile into a new file to be input into the gridding algorithm.

NED data within 1000 m of The National Aeronautics and Space Administration’s Shuttle Radar Mission Topography (SRTM) and NOAA NOAA’s National Ocean Service (NOS) Coastal Services Center (CSC) coastal LIDAR data were removed to avoid overlapping.

For more information on blockmedian and manual data removal, see Common Processing Steps and Data.
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