TOPOGRAPHIC MAPPING OF MARS:
FROM HECTOMETER TO MICROMETER SCALES
RL. Kirk", S. W. Squyres”, G. Neukum/, and the MER Athena and MEX HRSC Science Teams
Us. Geological Survey, 2255 N. Gemini Dr., Flagstaff, Arizona 86001 USA — rkirk@usgs.gov
Cornell University Dept. of Astronomy, Ithaca, New York, USA — squyres@astro.cornell.edu
“Freie Universitit, Institute for Geosciences, Berlin, Germany — gneukum@zedat.fu-berlin.de
Commission IV, WG IV/9
KEY WORDS: Extraterrestrial, planetary, Mars, topography, photogrammetry, cartography, remote sensing, exploration
ABSTRACT:
We describe USGS topomapping of Mars at resolutions from 100 m to 30 uum with data from the latest spacecraft missions.
Analysis of NASA 2001 Mars Odyssey Thermal Emission Imaging System (THEMIS) data combining daytime visible
reflected, daytime IR emitted, and nighttime IR emitted images allows us to isolate the physical effects of topography, albedo,
and thermal inertia. To a good approximation these physical influences interact linearly so that maps showing topographic
shading, albedo, and relative thermal inertia can be produced by simple algebraic manipulation of the corcgistered images.
The shading map resembles an airbrush shaded relief portrayal of the surface, and can be used as the input for quantitative
reconstruction of topography by photoclinometry (PC) at 100-m resolution over most of the planet.
The High Resolution Stereo Camera (HRSC) of the ESA Mars Express orbiter includes a 9-line scanner for color and stereo
imaging and a Super-Resolution Channel (SRC). We analyze these images with a combination of USGS ISIS cartographic
software and commercial photogrammetric software, providing an independent check on the stereo processing pipeline
developed by the HRSC team. In particular, we are producing very high resolution digital elevation models (DEMs) from the
SRC images by photoclinometry and by stereoanalysis, using Mars Orbiter Camera images to complete the stereopair.
The NASA Mars Exploration Rovers (MER) carry a diverse sct of cameras: two wide-angle hazard camera pairs, panoramic
stereo imagers (Pancam and Navcam), and a Microscopic Imager (MI) that images a 3-cm-square area at 30 um/pixel resolution.
Our work emphasizes MI data and includes geometric calibration, bundle-adjustment, mosaicking, generation of DEMs by
stereoanalysis and focal sectioning, and combination of MI images with color data from Pancam. The software being
developed to support these analyses can also be used to produce high-precision controlled mosaics, DEMs, and other
products from the Pancam and Navcam images.
1. INTRODUCTION 2. 2001 MARS ODYSSEY ORBITER THEMIS
The four spacecraft sent from Earth to Mars during the 2001 2.1 Source Data
and 2003 opportunities each carry novel imagers that open
up new possibilities for topographic mapping of Mars. In The NASA 2001 Mars Odyssey Orbiter began its mapping
this paper we describe the techniques that we are developing mission in February 2002. The THEMIS instrument on
at the U.S. Geological Survey in order to exploit these Odyssey acquires images (Christensen et al., 2003) in both
datasets and show examples of the results. A noteworthy visible and thermal infrared wavelengths. Visible-light (VIS)
aspect of the work described here is the enormous range in images can be acquired in five spectral bands (0.43-0.86 um)
spatial scales at which mapping is possible. The THEMIS although a single image in Band 3 (a red band ~0.65 wm) 1s
imagery is relatively low resolution and nonstereo but we usually collected. This band is ideal for our work because it
have developed a novel processing technique that shows surface albedo variations with high contrast and
effectively "strips away" the albedo variations that normally signal/noise ratio. VIS image strips are ^18 km wide with
limit photoclinometry (or "shape-from-shading") tech- resolution of —18 m/pixel. The IR images are of lower
niques to small areas of more uniform properties. The resolution (~100 m/pixel), cover a wider swath (~32 km),
dataset and method make topographic mapping of most or and can be acquired in 9 bands between 6.8-14.9 um. For the
all of the planet at hectometer resolution possible for the work described here we use only Band 9 (~12.6 wm), which is
first time. The HRSC multiline stereo scanner is the first always acquired and which has the highest signal/noise for
instrument of its kind to be used in planetary exploration, targets at or below 230 K. The VIS images and daytime IR
and is returning color and robust, single-pass stereo imagery images that we use were acquired simultaneously; those
of large areas of Mars at decameter resolutions. We have collected at equatorial latitudes have solar incidence angles
developed an independent processing capability for these between ~45° and ~75° (between ~15 h and 16:30 h local
images, but our efforts are currently focused on our unique time). The nighttime IR images are acquired on the opposite
capabilities within the HRSC team for topographic mapping part of the orbit (i.e. between ~3 h and 4:30 h).
with images from the SRC at resolutions of a few meters. The
MER rovers achieve higher resolution yet from their 2.2 Physical Basis of the Method
positions on the surface of Mars. In particular, the
Microscopic Imager is also the first instrument of its kind A necessary condition for analysis described here is the
on Mars and has an unprecedented 30 um resolution. The match between the number of available THEMIS datasets
other cameras on the rovers bridge the gap between this scale (VIS, day IR, and night IR) and the number of dominant
and what can be seen from orbit. The software and physical influences on these observables: surface
procedures we are developing for MER allow us to work orientation, albedo, and thermophysical properties in the
flexibly with images from all of the onboard cameras, guise of thermal inertia (Elachi, 1987). Thermal inertia (^
individually or in combination. units are J m^? sec? K!) is equal to V(kpep), where k is the
. Corresponding author.
834
dc
ab
