Office of Geomatics

Enabling GEOINT accuracy through geodetic, geophysical and photogrammetric sciences and content.

"Geodesy remains our life blood"

-- Robert Cardillo, NGA Director
The Director's Intent, 10/3/14
Products and/or services described may only be available to authorized customers.

Elevation

The NGA Office of Geomatics provides foundational expertise for the production, validation and management of terrain elevation content in support of academia, disaster relief, humanitarian aid, international cooperation, scientific research, and national security objectives. NGA provides expertise in the development, assessment and integration of elevation processes, specifications, and sources.


ArcticDEM

ArcticDEM is a National Geospatial-Intelligence Agency and National Science Foundation (NSF) public-private initiative to automatically produce a high-resolution, high-quality digital surface model (DSM) of the Arctic using optical stereo imagery, high-performance computing and open source photogrammetry software. NGA and NSF partnered with the University of Minnesota and other members of the academic research community, private sector and international partners to create this first-ever publicly available, high-resolution, satellite-based elevation dataset.

ArcticDEM data depicts the reflective surface and includes a collection of time-dependent, 2-meter DEM strips and an 8-meter seamless mosaic that can be distributed without restriction. ArcticDEM data will encompass all land area north of 60° north latitude. In addition, coverage will include all territory of Greenland, the entire state of Alaska, and the Kamchatka Peninsula of the Russian Federation. The producers did not intend the final product to be a single "eyes on" or edited product, but rather a collection of time-dependent elevation models and the infrastructure to process the flow of imagery from an ever-expanding constellation of satellites producing an ever-increasing volume of high-quality data.

See NGA's Arctic Support page for additional information.

Digital Terrain Elevation Data (DTED)

DTED is a uniform matrix of terrain elevation values and provides basic quantitative data for systems and applications that require terrain elevation, slope, and gross surface roughness information. DTED products are produced at three levels of resolution described below:

  • DTED Level 0 corresponds to small scale hardcopy products, and has a post spacing of 30 arc-seconds, or one kilometer nominal resolution.
  • DTED Level 1 corresponds to medium scale hardcopy products, and has a post spacing of three arc-seconds, or 100 meter nominal resolution.
  • DTED Level 2 corresponds to medium to large scale hardcopy products, and has a post spacing of one arc-second, or 30 meter nominal resolution.

Distribution of DTED and the Digital Data Products catalog is authorized to the Department of Defense, U.S. DOD contractors, and to U.S. Government agencies that support DOD functions (by authority of the Director, National Geospatial-Intelligence Agency, 30 May 1990).

Digital Bathymetry and Elevation Data (DBED)

DBED is a point prediction of global bathymetry and elevation values in meters stored in the format of DBED Level 0. It allows for a gross representation of the Earth's physical surface for general model and assessment activities. DBED is currently based upon the WGS 84 Earth Gravity Model 1996 (EGM 96).

Shuttle Radar Topography Mission (SRTM)

The SRTM mission began in 2000 as a joint venture between NASA and NGA to use a modified radar system onboard the Space Shuttle Endeavour to acquire reflective surface elevation data for over 80 percent of the Earth's land mass. SRTM data is available at two resolutions: 1 arc-second (nominal 30-meter) and 3 arc-seconds (nominal 90-meters). As part of an ongoing commitment to open data and international data sharing, SRTM datasets were released to the public and are currently available through USGS's Earth Explorer website.

TanDEM-X (SRTM)

TanDEM-X data is a reflective surface elevation dataset produced at a ground sample distance of approximately 12 meters. TanDEM-X data may be either raw (TDR) or finished (TDF). The TDR product is the result of a fully automated processing chain and may still contain undesirable artifacts. NGA participates in the TanDEM-X High Resolution Elevation Data Exchange Program established to produce a seamless, homogenous, edited TDF product from the initial raw data.

Elevation Surface Types: Digital Surface Model (DSM) vs. Digital Terrain Model (DTM)

Digital elevation models (DEM) are divided into two different surface types: reflective and bare earth. A bare earth DEM, also known as a digital terrain model (DTM), portrays what the terrain would look like if all vegetation and cultural features are removed. This surface type can be used to determine slope and characterize terrain. A reflective surface DEM, also known as a digital surface model (DSM), portrays vegetation and cultural features such as buildings. This type of data may be used for general situational awareness, navigation and detection of vertical obstructions.

Data Type: Finished vs. Raw

Finished data products are created or derived from a raw format, processed, and then finished to a certain product specification. Raw data do not conform to the same strict standards as finished products and users should be aware of potential data errors when using raw data which may include:

  • Spikes and Wells
  • Void
  • Missing or incorrectly portrayed landforms
  • Random Noise
  • Unfinished hydrology. Most methods used to create raw elevation data do not detect or process hydrology. Hydrology surfaces may be represented as void or noise in raw data.
Levels of Data Resolution

Level of data resolution refers to the ground sampling distance, or post-spacing, of elevation data. Resolution is typically defined in either geographic reference (arc second), or rectangular grid (precise meter) spacing. A smaller post-spacing gives the data a higher resolution and therefore more terrain detail. High resolution data comes with a price in terms of larger file sizes, potential increase in processing times, limited coverage areas, and typically higher production costs. The following table defines data levels and resolutions:

Level
Post Spacing
Arc-Seconds
0
1
2
3
4
5
Approximately 1,000 meters
Approximately 100 meters
Approximately 30 meters
Approximately 12 meters
Approximately 3 meters
Approximately 1 meter
30 Arc seconds
3 Arc seconds
1 Arc seconds
0.4 Arc seconds
N/A
N/A
Elevation Accuracy

Closely related to resolution is accuracy. The accuracy of an elevation dataset is defined in terms of Absolute Horizontal, Absolute Vertical, and Relative Vertical. Absolute Horizontal accuracy refers to how well the latitude and longitude (y, x) location of each elevation value is known. A better horizontal accuracy means that ridgelines and other features are more likely to be correctly positioned with respect to the horizontal datum. The absolute vertical accuracy refers to how well the published elevation is known with respect to the vertical datum. In other words, how close to the actual ground surface is to the published elevation. This is in contrast to the relative vertical accuracy which describes how accurate an elevation value is in relation to its neighboring elevations. Accuracies for elevation products are published at the 90% level, meaning that the given elevation is within plus or minus the stated accuracy 90% of the time.

Data Downloads

Data downloads require PKI certs. NGA products can be downloaded using the GEOINT Delivery Platform (GDP) and the Map of the World (MoW) "Download NGA Products" plugin.

  • GDP Home Page
  • MoW
    • Click the "Plugins" icon:
      MoW plugin icon
    • Click the "Download NGA Products" icon:
      MoW plugin icon
    • Click the desired product type:
      MoW product download types
    • Click the "eye" icon next to the desired product to begin the download:
      MoW eye icon
Services

Services require PKI certs and allow visualization via the IC Portal or ArcGIS desktop (download). After selecting the link below, additional viewing options may be available by following the link under the "Map Contents" heading.

Link
Description

Service info for elevation data sources used by the GVS basemap products. This service provides three different views of elevation datasets used to create the tinted hillshade for several GVS basemaps.

DBED0 is a global uniform matrix of digital bathymetry and elevation information that seamlessly represents the positive and negative heights of the Earth's physical surface above and below the oceans.

DTED is a uniform matrix of terrain elevation values. It provides basic quantitative data for all military systems that require terrain elevation, slope, and gross surface roughness information.

TERRAFORM is a Digital Elevation Model (DEM) data set in support of orthorectification activities.

SRT1F/SRTM2F is the finished production set of data where most of the voids have been filled. ALL SRTM DTED elevations are with respect to the reflective surface.

Worldwide basemaps depicting shaded relief derived from NGA's 1 kilometer and 90 meter TERRAFORM DTED, 30 meter TERRAFORM DTED2, NASA and METI's 30 meter ASTER GDEM v2 (used where TERRAFORM data is not available), USGS' 10 meter National Elevation Dataset (NED), NGA's Digital Bathymetric Elevation Dataset (DBED, 1 Kilometer), and NOAA's 90 meter coastal bathymetry (U.S. Coastal Relief Model).

POINT OF CONTACT
NGA Public Affairs
publicaffairs@nga.mil
Phone: 571-557-5400
Last modified: 07-Dec-17