baalke@mars.jpl.nasa.gov (Ron Baalke) (02/17/91)
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MAGELLAN IMAGES
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I've placed two more Magellan images at the Ames SPACE archives, bringing
the Magellan total to 10 images. They can be obtained through the usual
anonymous ftp access at ames.arc.nasa.gov (128.102.18.3) and are in the
ftp/pub/SPACE/VICAR directory. The two new files are called perspect.img
and saca.img. Like the other images, these images are in VICAR format, and
they have corresponding ASCII files (perspect.txt and saca.txt) that describe
the images. I've appended the two new text files at the end of this message.
The perspect.img file is 1MB in size, and the saca.img file is 2.8 MB
(yes, that's right, 2.8 MB). The perspect.img is particulary interesting,
because it a 3-D perspective created by combining Magellan radar imagery with
altimetry data (surface elevation measurements) taken by Pioneer Venus in 1979.
With this combination, additional information can be extracted out of the data,
such as a peak that appears in the 3-D view that is not visible by looking at
the Magellan image by itself. This peak is probably a volcano. The black
stripes in the image are gaps in the Magellan data. This image has already
appeared in a number of magazines and newspapers.
The images can be viewed in the VICAR format on an IBM PC computer with
the IMDISP program stored in a zip file called imdisp56.zip in the
ftp/pub/SPACE/IMDISP directory. I've also converted all of the Magellan
images (including the two new ones) into GIF files, and they are stored
in the ftp/pub/SPACE/GIF directory.
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PERSPECT.TXT
Perspective view of the southern boundary of Lakshmi Planum,
Ishtar Terra, Venus.
The southern scarp and basin province of western Ishtar
Terra in the northern hemisphere of Venus is portrayed in this
three-dimensional perspective view of Magellan radar image data.
Western Ishtar Terra is an Australia-sized highland terrain that
is a major focus of Magellan investigations. The highland is
centered on a 2.5-to 4-kilometer-high (1.5 -to 2.5- miles-high)
plateau, Lakshmi Planum, which can be seen in the distance and to
the right. Along this part of the Planum, the surface of the high
plateau drops precipitously into the bounding lowlands, with
slopes that exceed 5 percent over 50 kilometers (30 miles). The
numerous fractures and valleys located on and adjacent to the steep
outer slope of the plateau are clues to the formation of this
unusually abrupt topographic drop. Along other parts of the
boundary of Lakshmi are mountain ranges that rise as much as 6
kilometers (3.5 miles) above the plateau surface to over 11,000
meters (35,000 feet) above the mean elevation of the surface of
Venus. One of these mountain ranges, Danu Montes, rises over 1.5
kilometers (1.0 mile) above the plateau and can be seen in the
upper center of the image.
Images such as this one show the relationship of geological
features to topography and yield a valuable new perception of the
radar data. For example, the small dome-shaped high (center
left) is a volcano that is not apparent in the normal map-view
display of Magellan images. Only when combined with topography
in this fashion is the nature of the feature clearly evident.
These perspective views also display fractures of the surface in
their actual topographic setting. Understanding the relationship
of topography to these fractures, which express the stresses and
motions in the outer layers of the planet, helps geologists and
geophysicists to formulate and test models for the formation of
western Ishtar. The results of these studies will add to our
understanding of the interior forces that shape the surface of
Venus.
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SACA.TXT
This Magellan image reveals Sacajawea Patera, a large,
elongate caldera located in Western Ishtar Terra on the smooth
plateau of Lakshmi Planum. The image is centered at 64.5 degrees
North latitude and 337 degrees East longitude. It is approximately
420 kilometers (252 miles) wide at the base. Sacajawea is a
depression approximately 1-2 kilometers (0.6 -1.2 miles) deep and
120 x 215 kilometers (74 x 133 miles) in diameter; it is elongate
in a southwest-northeast direction. The depression is bounded by
a zone of circumferential curvilinear structures interpreted to be
graben and fault scarps. These structures are spaced 0.5-4
kilometers (0.3-2.5 miles) apart, are 0.6-4.0 kilometers (0.4-2.5
miles) in width and up to 100 kilometers (62 miles) in length.
Extending up to approximately 140 kilometers (87 miles) in length
from the southeast of the patera is a system of linear structures
thought to represent a flanking rift zone along which the lateral
injection and eruption of magma may have occurred. A shield
edifice 12 kilometers (7 miles) in diameter with a prominent
central pit lies along the trend of one of these features. The
impact crater Zlata , approximately 6 kilometers (4 miles) in
diameter is located within the zone of graben to the northwest of
the patera. Few flow features are observed in association with
Sacajawea, possibly due to age and state of degradation of the
flows. Mottled bright deposits 4-20 kilometers (2.5-12 miles) in
width are located near the periphery and in the center of the
patera floor within local topographic lows. Diffuse patches of
dark material approximately 40 kilometers (25 miles) in width are
observed southwest of the patera, superposed on portions of the
surrounding graben. The formation of Sacajawea is thought to be
related to the drainage and collapse of a large magma chamber.
Gravitational relaxation may have caused the resultant caldera to
sag, producing the numerous faults and graben that circumscribe the
patera. Regions of complex, highly deformed tessera-like terrain
are located north and east of the patera and are seen in the upper
portion of the image. Color has been added to this image to
simulate the appearance of the Venus surface.
___ _____ ___
/_ /| /____/ \ /_ /| Ron Baalke | baalke@mars.jpl.nasa.gov
| | | | __ \ /| | | | Jet Propulsion Lab | Is it mind over matter,
___| | | | |__) |/ | | |___ M/S 301-355 | or matter over mind?
/___| | | | ___/ | |/__ /| Pasadena, CA 91109 | Never mind.
|_____|/ |_|/ |_____|/ | It doesn't matter.spencer@eecs.umich.edu (Spencer W. Thomas) (02/20/91)
Ok, who's got a viewer/specs/converter for VICAR format? (Yes, I checked the FAQ posting.) Please respond by mail, I'll summarize. -- =Spencer W. Thomas EECS Dept, U of Michigan, Ann Arbor, MI 48109 spencer@eecs.umich.edu 313-936-2616 (8-6 E[SD]T M-F)
baalke@mars.jpl.nasa.gov (Ron Baalke) (02/20/91)
In article <SPENCER.91Feb19164832@spline.eecs.umich.edu> spencer@eecs.umich.edu (Spencer W. Thomas) writes: >Ok, who's got a viewer/specs/converter for VICAR format? (Yes, I >checked the FAQ posting.) > You can use the IMDISP program on an IBM PC to view the Magellan images in VICAR format. I am one of the programmers for IMDISP. You can get the program at ames.arc.nasa.gov (128.102.18.3) and it is in the pub/SPACE/IMDISP directory in the file imdisp56.zip. ___ _____ ___ /_ /| /____/ \ /_ /| Ron Baalke | baalke@mars.jpl.nasa.gov | | | | __ \ /| | | | Jet Propulsion Lab | Is it mind over matter, ___| | | | |__) |/ | | |___ M/S 301-355 | or matter over mind? /___| | | | ___/ | |/__ /| Pasadena, CA 91109 | Never mind. |_____|/ |_|/ |_____|/ | It doesn't matter.