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Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!caen!ox.com!msen.com!emv
From: baalke@mars.jpl.nasa.gov (Ron Baalke)
Subject: [graphics] Magellan Images
Message-ID: <1991Mar26.004118.5633@ox.com>
Followup-To: comp.graphics
Keywords: Magellan
Sender: emv@msen.com (Edward Vielmetti, MSEN)
Reply-To: baalke@mars.jpl.nasa.gov (Ron Baalke)
Organization: Jet Propulsion Laboratory, Pasadena, CA.
References: <1991Mar25.012512.23477@jato.jpl.nasa.gov>
Date: Tue, 26 Mar 1991 00:41:18 GMT
Approved: emv@msen.com (Edward Vielmetti, MSEN)
X-Original-Newsgroups: comp.graphics

Archive-name: astro/magellan/magellan-images/1991-03-25
Archive-directory: ames.arc.nasa.gov:/pub/SPACE/VICAR/ [128.102.18.3]
Original-posting-by: baalke@mars.jpl.nasa.gov (Ron Baalke)
Original-subject: Magellan Images
Reposted-by: emv@msen.com (Edward Vielmetti, MSEN)

                            ===================
                              MAGELLAN IMAGES
                              March 24, 1991
                            ===================
 
     I've placed five more Magellan images in VICAR format and 18 in GIF format
at the Ames SPACE archives, bringing the Magellan total to 19 VICAR images and
46 GIF images.  All of the images are obtainable via anonymous ftp from
ames.arc.nasa.gov (128.102.18.3), and are in the pub/SPACE/VICAR and
pub/SPACE/GIF directories, respectively.  All of the Magellan images I've
uploaded to Ames are public release images from the Magellan project, and
are in the public domain and can be freely distributed.
 
     The five new VICAR files and their sizes are:
 
        alpha.img       1,049,600 bytes
        lavin.img       1,049,600 bytes
        ovdac.img       1,574,400 bytes
        ovdan.img       3,147,776 bytes
        tick.img        2,347,458 bytes
 
     All of the VICAR images have a corresponding caption files (with a .txt
extension) which contains detailed descriptions of the image.  Make sure
you are in binary mode when transferring the image files, and in ASCII mode
when transferring the text files.  The new caption files are appended to
the end of this message.
 
     The VICAR images can be viewed on an IBM PC computer with the IMDISP
program stored in a zip file called imdisp56.zip, located in the
pub/SPACE/SOFTWARE directory.  I am one of the programmers for IMDISP, and
would welcome any feedback on the program.  The VICAR format is used by the
Image Processing Lab (MIPL) at JPL.  Most of the VICAR images are in 1024x1024
pixel resolution and are about 1MB in size.
 
     I've converted all of the Magellan VICAR images into GIF format in
640x480, 256 color resolution.  The new GIF files are:
 
          alpha.gif            ovdac.gif
          alpha1.gif           ovdac1.gif
          alpha2.gif           ovdac2.gif
          alpha3.gif           ovdac3.gif
          lavina.gif           ovdan.gif
          lavina1.gif          ovdan1.gif
          lavina2.gif          ovdan2.gif
          tick.gif             ovdan3.gif
          tick1.gif
          tick2.gif
 
============================================================================
ALPHA.TXT
 
     Thirty-six orbits of full-resolution data from the northern
edge of central Alpha Regio are shown in this image.  The image
width is about 600 kilometers (375 miles).  The bright lineated
terrain is a series of troughs, ridges, and faults that are
oriented in many directions.  The lengths of these features
generally range from 10 kilometers (6.3 miles) to 50 kilometers
(31.3 miles).  The topographic elevation within Alpha Regio varies
over a range of 4 kilometers (2.5 miles).  Local topographic lows,
whose outlines are generally controlled by structures within the
central region, are relatively radar-dark and filled with volcanic
lavas.  Source vents for this volcanism appear as bright spots
within the smooth plains units.  A distinct example of late-stage
deformation of Alpha is the narrow band of southwest-northeast
trending faults that disrupt older terrain between -20 degrees and
-22 degrees latitude.  Another interesting feature is the 35
kilometers (21.9 miles) diameter volcanic edifice located at the
upper right of the image.  The center of the volcano is a local
topographic low and its western edge appears to be breached.
============================================================================
LAVIN.TXT
 
     This Magellan image mosiac located in the Lavinia region shows
the crater Carson, a 38 km (23 mile) diameter crater.  The image is
centered at about 24 degrees south latitude, 344 degrees longitude. 
Impact craters in the Magellan data are frequently surrounded by
radar-dark halos.  Several of these halos were noted to have a
hyperbolic shape, extending hundreds of kilometers to the west of
the craters.   Five of these dark halos were also seen extending
out from craters in Magellan emissivity data.  Magellan emissivity
data, derived from the altimeter data, provides information about
the porosity (soil versus solid rock) and the composition of the
surface.  The darkness in the emissivity data indicates a very
smooth surface, leading to the interpretation that these halos may
be thick, smooth sediment deposits formed by the 'crushing' blow of
the atmosphere associated with the incoming projectile that formed
the impact crater.  But why are only about 5% of the craters
surrounded by these halos?  On the surface of most planets, the
population of impact craters can be used to obtain both relative
and absolute surface ages.  On Venus, as on Earth, there are
relatively few craters, making relative age dating (comparing one
region of the planet to another) statistically difficult.  The
number of craters on Venus indicates that the surface may  be only
about 400 million years old.  The dark halos may indicate the very
youngest craters on the planet-  where the harsh conditions on
Venus have not yet caused these dark halos to 'roughen up' and
disappear.  The halos could possibly be used as 'geologic clocks.'
Volcanic flows or tectonic structures cutting one of these halos
are interpreted to have occurred even more recently than the
craters.  This image shows such a situation, where flows associated
with the crater cut across the halo, indicating a very young age.
Scientists are continuing to identify these halos in the Magellan
data, and use them to understand the geologic evolution of the
surface.
============================================================================
OVDAC.TXT
 
     This Magellan image shows part the interior of Ovda Regio, one
of the large highlands ringing the equator of Venus.  Several
tectonic events formed this complex block-fractured terrain.  An
underlying fabric of ridges and valleys strikes NE-SW.  These
ridges are spaced 10-20 kilometers (6-12 miles) apart and may have
been caused by shortening of the crust at right angles to this
trend.  These structures are cut by throughgoing extension
fractures trending NW-SE, suggesting a later episode of NE-SW
extension.  Lastly, the largest valleys, particularly the 20
kilometer (12 mile)-wide one extending across the image, were
filled with dark material, probably lava.  The complex internal
fabric of Ovda Regio attests to a long history of tectonic
deformation.  This image, centered approximately at 1 S 81 E,
measures 225 kilometers (140 miles) by 150 kilometers (90 miles)
and was acquired by Magellan in November 1990.
============================================================================
OVDAN.TXT
 
     This Magellan image shows part of the northern boundary of
Ovda Regio, one of the large highlands ringing the equator of
Venus.  The scene consists largely of low-relief, rounded linear
ridges.  These ridges, 8-15 kilometers (5-9 miles) in width and
30-60 kilometers (20-40 miles) long, lie mostly along a 100-200
kilometer (60-120 mile) wide slope where the elevation drops 3
kilometers (2 miles) from Ovda Regio to the surrounding plains. 
Some of the ridges have been cut at right angles by extension
fractures.  Dark material, either lava or windblown dirt, fills the
region between the ridges.  The curvilinear, banded nature of these
ridges suggests that crustal shortening, roughly oriented
north-south, is largely responsible for their formation.  Such
crustal shortening was unexpected by Magellan scientists, who
believed that Ovda Regio, a likely site of hot upwelling from the
interior of Venus, should be dominated by volcanism and crustal
extension.  This image, centered approximately at 1 N 81 E,
measures 300 kilometers (190 miles) by 225 kilometers (140 miles)
and was acquired by Magellan in November 1990.
============================================================================
TICK.TXT
 
     This Magellan image is located in the Eistla Region of Venus
in the southern hemisphere and is centered at 5.5 degrees east
longitude, 18 degrees south latitude.  It is 122.8 kilometers (76.1
miles) across east-west and 107.5 kilometers (66.6 miles) across
north-south.  North is oriented towards the top of the image.  
 
     Shown in the image is an unusual volcanic edifice unlike all
others previously observed.  It is approximately  65.6 kilometers 
(40.7 miles) across at the base and has a relatively flat, slightly
concave summit 34.8 kilometers (21.6 miles) in diameter.  The sides
of the edifice are characterized by radiating ridges and valleys
that impart a fluted appearance to the construct.    
 
     To the west, the rim of the edifice appears to have been
breached by dark lava flows that emanated from a shallow summit pit
approximately 5.4 kilometers (3.3 miles) in diameter and traveled
west along a channel approximately 5.4 kilometers (3.3 miles) wide
and 26.8 kilometers (16.6 miles) long.  A series of coalescing,
collapsed pits 2-10 kilometers (1.2-6.2 miles) in diameter are
located 10 kilometers (6.2 miles) west of the summit rim.
 
     The edifice and western pits are circumscribed by faint,
concentric lineaments up to 70.3 kilometers (43.6 miles) in
diameter.  A series of north-northwest-trending graben are
deflected eastwards around the edifice; the interplay of these
graben and the fluted rim of the edifice produce a distinctive
scalloped pattern in the image.  Several north-northwest-trending
lineaments cut directly across the summit region.  
 
     This peculiar volcanic construct is located 25-30 kilometers
(15.5-18.6 miles) north of Alpha Regio, a highly deformed region of
tessera terrain.  A collection of at least 6 similar volcanoes has
been observed near Thetis Regio, a region of tessera within
Aphrodite Terra.  Thus, these unusual  constructs tentatively
appear to be spatially associated with regions of tessera.  The
implications of this spatial association on the unusual morphology
of these constructs are being investigated.
      ___    _____     ___
     /_ /|  /____/ \  /_ /|      Ron Baalke         | baalke@mars.jpl.nasa.gov
     | | | |  __ \ /| | | |      Jet Propulsion Lab | 
  ___| | | | |__) |/  | | |___   M/S 301-355        | Change is constant. 
 /___| | | |  ___/    | |/__ /|  Pasadena, CA 91109 | 
 |_____|/  |_|/       |_____|/                      | 

