SRTMIMGR v003

NASA Shuttle Radar Topography Mission Swath Image Data Set


PI: Michael Kobrick, Robert Crippen

Description

The Land Processes Distributed Active Archive Center (LP DAAC) is responsible for the archive and distribution of NASA Making Earth System Data Records for Use in Research Environments (MEaSUREs) SRTM, which includes the global 1 arc second (~30 meter) swath (raw) image data product. (See User Guide Section 2.2.1)

The SRTM swath image data set consists of radar image files containing brightness values, as well as quality assurance (incidence angle) files for each of four overlapping sub-swaths that passes through a 1 degree by 1 degree tile. Data from each sub-swath is included as a separate file. Some files may contain only partial data; however, every image pixel acquired by SRTM is included in this data set.

The NASA SRTM data sets result from a collaborative effort by the National Aeronautics and Space Administration (NASA) and the National Geospatial-Intelligence Agency (NGA - previously known as the National Imagery and Mapping Agency, or NIMA), as well as the participation of the German and Italian space agencies. This collaboration aims to generate a near-global digital elevation model (DEM) of Earth using radar interferometry. SRTM was the primary (and virtually only) payload on the STS-99 mission of the Space Shuttle Endeavour, which launched February 11, 2000 and flew for 11 days.

The SRTM swaths extended from ~30 degrees off-nadir to ~58 degrees off-nadir from an altitude of 233 kilometers (km), creating swaths ~225 km wide, and consisted of all land between 60° N and 56° S latitude to account for 80% of Earth’s total landmass.

Characteristics

Improvements/Changes from Previous Versions

  • Version 3.0 products are filled with ASTER Global Digital Elevation Model (GDEM) Version 2.0, the Global Multi-resolution Terrain Elevation Data 2010 (GMTED2010), and the National Elevation Dataset (NED).

Collection and Granule

Collection

Characteristic Description
CollectionMEaSUREs SRTM
DOI10.5067/MEaSUREs/SRTM/SRTMIMGR.003
File Size~2.38 MB
Temporal ResolutionMulti-Day
Temporal Extent2000-02-11 to 2000-02-21
Spatial ExtentGlobal (60°N to 56°S, 180°W to 180°E)
Coordinate SystemGeographic Latitude and Longitude
DatumWGS84/EGM96
File FormatMAG and INC
Geographic Dimensions1° x 1°

Granule

Characteristic Description
Number of Science Dataset (SDS) Layers2
Columns/Rows3601 x 3601
Pixel Size~30 m

Layers

SDS Name Description Units Data Type Fill Value No Data Value Valid Range Scale Factor
MAG Radar Sub-swath Brightness Values N/A 8-bit signed integer 0 N/A N/A N/A
INC Incidence Angle Degree 16-bit signed integer 0 N/A N/A N/A

Product Quality

Scientists used a method called Kinematic Global Positioning System Geodetic field surveying to validate the SRTM data. This method facilitates the very rapid long lines of precise positions from a moving vehicle. Several entities conducted the actual survey work, including private contractors, NGA geodesists and NASA Jet Propulsion Laboratory (JPL) scientists. In all, about 70,000 kilometers of survey lines were collected in support of this mission. The data were used to model long-wavelength error sources.

In addition, NASA’s JPL deployed corner reflectors during the mission. These are highly reflective structures that appear as a bright point in the radar image. These reflectors deployed with precisely measured coordinates, served as control points in the Shuttle Radar Topography Mission data.

Speckle noise is present in the swath image data. This is a characteristic of coherent imaging systems and appears as a random, high-frequency, salt and pepper effect. Most imaging radar systems average many looks to reduce speckle, however SRTM was optimized for a wide swath and thus acquired only 1–2 looks per sub-swath causing a relatively high speckle noise level. This is one reason why the combined image data set, SRTMIMGM, was produced.

Known Issues

Known issues in the NASA SRTM are described in the following publication: Rodriguez, E., C. S. Morris, and J. E. Belz (2006), A global assessment of the SRTM performance, Photogramm. Eng. Remote Sens., 72, 249–260. https://doi.org/10.14358/PERS.72.3.249

Documentation

Using the Data

Tools

Citation

DOI: 10.5067/MEaSUREs/SRTM/SRTMIMGR.003

About the Image

Radar Sub-swath Brightness values over the Democratic Republic of the Congo, 2000.