This three-dimensional perspective view of the volcanic
island of
Manam, Papua New Guinea was obtained by a NASA imaging
radar
system onboard a DC-8 aircraft in November 1996.
The volcano,
one of the most active in the Pacific "Ring of
Fire," was in the
midst of its largest eruption since 1992 when this image
was
acquired. The island, approximately 10 kilometers
(6 miles)
across and 1800 meters (5900 feet) high, is actually
the top of a
much larger volcano that rests on the sea floor.
Lava flows and
hot clouds of rock, ash and gas known as pyrocalstic
flows are
emitted from craters at the summit of the volcano and
race down
the valleys. Two of the valleys are visible
as dark patches
near the summit. Deposits from earlier flows appear
orange and
blue; forested slopes of the volcano appear pink.
Two weeks
after this image was acquired, the eruption intensified,
killing
several people and forcing the evacuation of thousands
of others.
The topographic information in this image was obtained
using the
technique of radar interferometry, in which the reflected
radar
signals are recorded simultaneously by two antennas mounted
on
separate areas of the aircraft. This image
was acquired by
NASA's Airborne Synthetic Aperture Radar operated in
its
topographic TOPSAR mode on November 16, 1996. The
image is
centered at 4.1 degrees South latitude and 145.06 degrees
East
longitude; the image shows the eastern side of the volcano.
No
vertical exaggeration has been applied. The colors are
assigned
to different radar frequencies and polarizations of
the radar as follows: red is P-band (68 cm), horizontally
transmitted and vertically received; green is P-band,
vertically
transmitted and received; and blue is C-band
(6 cm), vertically transmitted and received.