Evaluation of the United States Geological Survey's 1-Arc Second National Elevation Dataset (NED) for propagation studies Donald Draper Campbell 19 May 2015

The National Elevation Dataset (NED) is the primary elevation data product of the United States Geological Survey (USGS). The NED is generated at various horizontal resolutions (NED layers) to serve the needs of local, regional and nationwide applications. Three of these layers are nationally seamless and are distributed in geographic coordinates at 1/3, 1, and 2 seconds of arc. They were originally created by USGS laying 1/3-second and 1-second grids over the 7.5-minute maps and extracting the data points, and by laying a 2-second grid over the 1:63,360 scale maps of Alaska. It should be noted that the USGS 3-Arc Second NED is no longer maintained by USGS, and that the 1-Arc Second NED is presently being maintained/updated as new data comes in as additional areas are re- surveyed. The following four slides provide information on areas updated, sources of elevation data, currency of data, and methods of production.

The FCC’s Office of Engineering and Technology (OET) is responsible for the analysis of the potential reconfiguration of television channel assignments in the spectrum allocated to the broadcast television service in the context of the Broadcast Television Incentive Auction. This analysis process required the creation of a new propagation analysis tool, TVStudy. In the past, prior television channel assignment analysis tools relied on the USGS 3-Arc Second NED. The new TVStudy program is capable of supporting the USGS 1-Arc Second NED, as well as the older 3-Arc Second NED. The new program defaults to the use of the 1-Arc Second NED and some users of the old software have raised concerns in switching from the 3-Arc Second NED. Using the National Geodetic Survey's (NGS) Survey Mark data set consisting of some 680,000 data points, we compared the USGS 3-Arc Second NED and the USGS 1-Arc Second NED. In a geodetic context, the terms “Survey Mark” and “Bench Mark” are not the same. A Bench Mark is a specific type of Survey Mark that has a known elevation above or below an adopted surface or datum. A Survey Mark refers to any permanent marks or disks placed in the ground or attached to a permanent structure with known latitude, longitude and height information. The 1-Arc Second NED more accurately represents the topography of the earth.

As visualized by the next four slides, the statistical distribution of errors in comparison with the Survey Mark data set is significantly higher in the case of the 3-Arc Second NED versus the 1-Arc Second NED. In comparing these maps, the 3-Arc Second map has more red dots (and deeper shade of red dots) then the 1-Arc Second. The differences between the elevations of the Survey Mark and the corresponding point from each dataset are in meters. Note the use of the same scale for both sets of maps. Quadrilinear interpolation was used to approximate the elevation from each terrain dataset at precisely the same locations as the benchmark point. Quadrilinear interpolation programs were developed by Nam Pham, another Senior Electronics Engineer in OET. The following four slide sdisplay the errors between the USGS terrain databases (3 and 1-Arc Second) and the National Geodetic Survey’s Survey Mark data set for both the 48 States and Alaska. The legends in each of the four images show the delta difference between USGS terrain databases and NGS Survey Mark data ranging from dark green (little error) to dark red (a great error) in meters along with the frequency of occurrence of error.

Error between USGS 3-Arc Second terrain database and NGS’s Survey Mark data set

Error between USGS 1-Arc Second terrain database and NGS’s Survey Mark data set

Error between USGS 3-Arc Second terrain database and NGS’s Survey Mark data set -- Alaska

Error between USGS 1-Arc Second terrain database and NGS’s Survey Mark data set -- Alaska

The Spectrum Utilization Study Software (SUSS) developed by OET, was used to create a database containing a number of geospatial data fields, including ground elevation above mean sea level for: – 1) all officially registered structures on which antennas of site-specific licensees were mounted along with – 2) unofficially reported locations of structures of commercial tower companies leased to site-specific and market-based licensees. Data is not available for structures on which wireless carriers own or lease structures on their own. A comparison of the ground elevation of these structures was made to the 1-Arc Second NED and the 3-Arc Second NED. It should be noted that this data set is not all-inclusive for market-based licensees, since such licensees do not have to report to the Commission the location of their base stations, nor can there be any guarantee on the accuracy of the self-reported data we do have.

Even considering that there may be some errors in this data set, it is apparent that the statistical distribution of errors in comparison with reported ground levels at these antenna structures is significantly higher in the case of the 3-Arc Second NED versus the 1-Arc Second NED. In comparing the maps on the next two slides, the 3-Arc Second map has more red dots (and deeper shade of red dots) then the 1-Arc Second. Again, the maps are of similar scales for comparison. Again, quadrilinear interpolation was used to approximate the elevation from each terrain dataset at precisely the same locations as the antenna structure locations. Quadrilinear interpolation programs were developed by Nam Pham, another Senior Electronics Engineer in OET.

The error between USGS 3-Arc Second terrain database and the Ground Elevation of Antenna Structures

The error between USGS 1-Arc Second terrain database and the Ground Elevation of Antenna Structures

The Spectrum Utilization Study Software (SUSS) is a suite of software tools that are designed to create a composite assignment database of all FCC licensing records, plus the records of the Antenna Structure Registration database. Additionally, the programs also creates a Tower Database, comprised of over 763,416 site records derived from FCC records. There is also a program in the SUSS suite that extracts record from about 50 commercial tower companies that have been posted the web consisting of over 250,000 antenna structure sites. Some of these records do not contain ground elevation information. The program makes a best attempt to match these records with FCC records. If a match is not found, the data is not added to the Tower Database, and there are 47,399 records of these over 250,000 entries that do not match FCC records. Many wireless carriers do not publish site location information on the web and there are smaller tower companies that may or may not have posted information on the web or I have not found them. The SUSS software can be downloaded from The TVStudy program is also available from the FCC's website at

The complete NED data sets can be either downloaded from the web site as individual data files (there several thousand) or can be acquired as a complete data set by contacting USGS. It should be noted that these data sets are not static, and are dynamically updated on a non-regular basis as new data are included. The current USGS point of contact is Charles Pederson or telling him what data sets and formats you Data Sets are: NED 2-Arc Second Alaska, NED 1-Arc Second, NED 1/3-Arc Second and NED 1/9-Arc Second and are available in the following formats: ArcGrid, GridFloat and IMG. You will be instructed to send a 4-TB USB hard drive and return postage to U.S. Geological Survey c/o Charles Pederson, Room Independence Road Rolla, MO

There is no charge for either data service regardless of customer type (commercial, private, government, educational). More detail information can be found on these two web pages Questions?