USGS Home
Contact USGS
Search USGS

Shuttle Radar Topography Mission Data (SRTM)

One of the unique characteristics of the SRTM dataset is that it was collected during an 11-day period, so it provides a recent topographic “snapshot” of the shape and condition of the land surface. As such, the SRTM data serve as the end member of a set of multitemporal elevation data that is useful for detecting and assessing the effects of topographic surface modifications over broad areas.

The figure below shows an overview of the SRTM data used for this study. Note the presence of several data voids in the SRTM coverage where interferometric radar data were not collected. Even though 99.96 percent of the targeted landmass was mapped by SRTM, a small shortage in the availability of instrument duty cycle hours during the mission meant that some areas could not be covered.

Shaded relief portrayal of the Shuttle Radar Topography Mission dataset.

Reference Geodetic Control Points
Detailed information about the absolute vertical accuracy of the NED and SRTM data is required for the change detection method. To calculate the requisite vertical accuracy measurements, the NED and SRTM were compared to an independent reference set of high accuracy geodetic control points from the National Geodetic Survey (NGS).

GPS on Bench Marks Dataset
The "GPS on bench marks" dataset, shown below, includes the points distributed throughout the conterminous United States that NGS uses for gravity and geoid modeling. They provide an excellent independent reference against which the NED and SRTM data can be assessed.

Distribution of reference geodetic control points.