These two images are two-dimensional (top) and three-dimensional
(bottom) views of the same area, southeast of Bhuj, India. Together they
demonstrate how NASA's Shuttle Radar Topography Mission (SRTM) elevation
models can be used to help in the interpretation of satellite imagery.
The image was acquired by the Landsat 7 satellite. The top view is a
standard panchromatic (visible and near infrared) satellite picture. The
bottom view is the same scene projected into an anaglyph, based upon
SRTM data. Anaglyphs are generated by creating two differing
perspectives of a single satellite image, one perspective for each eye.
Note that there are several dark lines crossing parts of the image. Some
of these lines are roads but some are geologic dikes. Dikes are
sheet-like rocks formed when volcanic fluids intrude cracks in older
host rocks. The intersections of these "sheets" with the topographic
surface appear as linear or curvilinear traces across the terrain. The
dikes traverse varied terrains and they intersect each other--much like
roads. In the two-dimensional view, roads and dikes are confusingly
similar in appearance. However, in three dimensions, dikes can be seen
to be ridge-forming features and geographically related to other
geologic features (left and lower right of image). In contrast, roads
generally traverse less rugged terrain and pass through ridge gaps
(upper right and left center of image). Thus the added topographic
information provided by SRTM greatly helps in the image interpretation.
The stereoscopic effect of this anaglyph was created by first draping a
Landsat satellite image (taken just two weeks after the earthquake) over
preliminary digital elevation data from the Shuttle Radar Topography
Mission (SRTM), and then generating two differing perspectives, one for
each eye. When viewed through special glasses, the result is a
vertically exaggerated view of the Earth's surface in its full three
dimensions. Anaglyph glasses cover the left eye with a red filter and
cover the right eye with a blue filter.
Landsat has been providing visible and infrared views of the Earth since
1972. SRTM elevation data matches the 30-meter (33-yard) resolution of
most Landsat images and will substantially help in analyses of the large
and growing Landsat image archive. The Landsat 7 Thematic Mapper image
used here was provided to the SRTM project by the United States
Geological Survey, Earth Resources Observation Systems (EROS) Data
Center, Sioux Falls, South Dakota.
Size: 13.8 x 9.6 kilometers ( 8.6 x 5.9 miles)
Location: 23.2 deg. North lat., 69.8 deg. East lon.
Orientation: North toward the top
Image Data: Landsat Panchromatic Band (visible and near infrared)
Date Acquired: February 2000 (SRTM), February 9, 2001 (Landsat)