Geology Reference
In-Depth Information
carried two high-quality camera systems, a panoramic cam-
era for detailed geologic studies and a metric (mapping)
camera that enabled topographic data to be derived. The
“
pan
”
camera, using a lens of focal length 610mm, was
highly sophisticated and obtained stereoscopic views of the
surface with resolutions as good as 1m from an orbital
altitude of 100 km. The camera rotated in a direction across
the path of the orbiting spacecraft, giving a panoramic view.
The Apollo metric image system consisted of two cam-
eras, one pointing downward and one pointing away
from the Moon. Both used 76mm lenses with the
upward-pointing camera being used to
fix precisely the
geometric position of the spacecraft in relation to the star
field and with the Moon
'
s surface being photographed by
the other camera. Although the spatial resolution of metric
frames is only about 20 m, the precision of location
enabled the production of high-quality maps.
The Lunar Orbiter and Apollo hand-held camera
images, and the Apollo 15
-
17 panoramic and metric cam-
era images, are being digitized under the direction of Mark
Robinson of Arizona State University, and are available
through NASAwebsites.
A2.1.2 Vidicon systems
The imaging system most widely used in Solar System
exploration in the 1970s and 1980s involved vidicon
cameras. These systems employed a small electron gun
and a photoconductor. The image was optically focused
onto the photoconductor so that a beam of electrons from
the gun was transformed into a current that varied with
the intensity of the light re
ected from the scene. This
current was in either analog (
ownonearlysystems,
such as the lunar Ranger landers) or digital format and
was either stored on board the spacecraft or transmitted
directly to Earth. The signals were transferred into pixels
and DN levels for computer processing.
A2.1.3 Facsimile systems
Facsimile cameras scan across the scene by rotating a slit
across the scene as a panorama. Facsimile cameras were
used on the two martian Viking lander spacecraft and on
the Soviet Venera landers on Venus. The returned data
were in pixel formats with DN levels.
