Featured Image (03/17/2009) - Over the Sea of Rains
Some of the Apollo Metric Camera Images were obtained while the
Command Module was rolled in order to move the Metric cameras in the
Service Module SIM Bay to a non-nadir orientation,
increasing the geographic extent of the photographic coverage. We have created a new browsing interface to
let users easily view these oblique frames, along with all of the other Apollo
Metric images released to date.
This spectacular oblique picture of the lunar surface shows the view
looking almost due north over Mare
Imbrium, one of the largest mare on the lunar nearside (Figure 1,
AS15-M-1555, collected by Astronaut Al Worden
aboard the Apollo 15 CSM Endeavour). We have discussed the
complex geology of this region of the Moon in a previous Apollo
Featured Image. The oblique nature of this image
enhances the dynamic, three-dimensional
nature of the lunar surface. In particular, you can
see the lobes of individual lava flows and the spectacular relief of the
lunar mare ridges (Figure 2). Large (bigger than
100km) craters are relatively rare on this mare surface, but numerous secondary
craters dot the landscape. Several small sinuous rilles can also be seen near the
bottom of this image.
Figure 1. An oblique view of northern Mare Imbrium. Individual lava
flows, secondary impact craters, sinuous rilles, and mare ridges
can be clearly seen (Apollo Image AS15-M-1555 [NASA/JSC/Arizona State University])
Changes in the
angle and the azimuth of the Sun can make it easier (or harder) to
derive the topography of the lunar surface through image data. In
this case, rolling the Apollo CSM changed the relative
angle between the Sun and the camera, which in turn made it much
easier for the lunar geoscientists analyzing this image to study the
geomorphology of some of the features in this region, especially when
combined with other Metric frames from the same region taken at
different sun angles.
Figure 2. Annotated version of Figure 1.
The dotted lines show the locations of some of the lava flows, sinuous
rilles, and geographic features visible in the
image (Apollo Image AS15-M-1555 [NASA/JSC/Arizona State University]).
Understanding the topography of a region is important for the
selection of lunar landing sites, lunar geoscience exploration
traverse planning, and geologic studies of the lunar surface.
As part of its mission to map the Moon to prepare for
the permanent return of Americans to the lunar surface, the Lunar
Reconnaissance Orbiter Camera [LROC] will be taking repeat
pictures with different solar incidence angles and solar azimuths of
high-priority sites for possible future human lunar exploration, a
technique informally known as photometric stereo. Since the LROC
instruments are body-fixed and nadir-pointing, the LRO itself will
also be rolled off-nadir to allow LROC to
collect high-resolution oblique views of select high-priority sites on
the lunar surface (a technique informally known as geometric stereo,
commonly used here on Earth for terrestrial applications). These
data will then be used by lunar scientists to derive high-resolution
(i.e., 3-5 meters/pixel) topographic data for potential sites of human
lunar activity to aid in mission planning.
Apollo Over the Moon: A View from Orbit (1978)
H. Masursky, G. W. Colton, F. El-baz, eds. NASA SP-362.