USGS 3D Elevation Program
Aerial LiDAR (ALS) elevation source data collections
In collaboration with federal, state, and local partners such as the United States Forest Service and Federal Emergency Management Agency, the USGS 3DEP Program offers up to 50% cost-match for LiDAR data collections. To produce a digital elevation model, Light Distance And Ranging technology uses lasers from an aerial platform such as an airplane. Individual reflected light returns form a "point-cloud", usually classified into groupings of ground, vegetation, water, and building points. Point clouds, often stored in compressed .LAZ file format as tiles of a larger collection area, are available for download from the National Map Downloader(elevation source data) or online viewing using tools such as Cesium and Potree now made possible through the development of Entwine Point Tiles file format and collaboration, see [ https://usgs.entwine.io/].
Lasers from SPACE, the future to come?
Space-based LiDAR systems such as the GEDI instrument on the International Space Station produce a full-waveform product that is available in strips along the instrument track. Large-extent products from full-waveform instruments generally are not available; the data is generally used to calibrate elevation or vegetation models in collaboration with data from other sensors such as passive multispectral instruments on the LANDSAT and SENTINEL missions.
Past, Present and Future
USGS 3DEP is designed to replace the National Elevation Dataset (NED) originally based on data collected in the Shuttle Radar Topography Mission (SRTM) which made available first a 30m resolution and later a 10m digital elevation model for the United States. The continental-scale USGS 3DEP dataset, once completed, will serve the basis for updates to the National Hydrography Dataset, known as NHD 3D which will replace the NHDPlus HR dataset as the most high resolution modelled hydrographic data product available from the USGS.
Alaska IFSAR Data
SAR, Synthetic-aperture radar, or InSAR/IFSAR, Interferometric synthetic aperture radar, is another remote sensing methodology for collecting high resolution elevation data. The USGS used IFSAR-based topography data collections for Alaska with the end goal of producing a 5m resolution digital elevation product. The USGS Earth Observation and Remote Sensing Lab (EROS) completed this work in 2020.
Using the USGS 3DEP Digital Elevation Model
The most common visualizations for digital elevation models are hillshade, slope and aspect functions which represent terrain as lit by the sun's illumination; the degrees or percent rise of the terrain; and the compass orientation of the slope of the terrain. The USGS 3DEP Explorer web tool allows online visualization of the digital elevation model using these functions. These visualizations are also available through a web map service from the National Map, which can be loaded within JOSM as a custom imagery source (only the multidirectional hillshade option is available as a preset imagery source) or added as a custom background within the OpenStreetMap online iD Editor:
(Go to Background Settings, Custom, and enter this URL:
Hillshade Multidirectional in the URL can also be replaced by other types of visualizations:
- Aspect Degrees
- Aspect Map
- Hillshade Elevation Tinted
- Hillshade Gray
- Hillshade Multidirectional
- Slope Degrees
- Slope Map
Individual DEM tiles or collections of tiles using custom extents can be downloaded from the National Map Downloader by specifying a search by datasets from Elevation Data Sources-> Original Product Resolution Files. OpenTopography also offers an access portal to the USGS 3DEP data as well as other similar datasets, with the added bonus of offering on-demand, cloud-based hydrologic modelling tools, free to those with academic institution email addresses.
The horizontal accuracy of the 3DEP data is not specified, but it's typically less than 1 m error. It can be estimated from the flying altitude, which is specified in the mapping report for each region:
|Altitude (m)||Positional RMSEr (cm)|
Note that it appears that detached blocks of rock are removed from the dataset, possibly as part of a building-removal algorithm.