MARS: HIGH-RESOLUTION DIGITAL TERRAIN MODEL AND ORTHO-IMAGE
MOSAIC ON THE BASIS OF MEX/HRSC DATA
A. Dumke 1 *, M. Spiegel 1 , R. Schmidt 2 , G. Michael 1 , G. Neukum 1
‘institute of Geosciences, Planetary Sciences and Remote Sensing, Freie Universität Berlin,
Malteserstr. 74-100, 12249 Berlin, Germany -
{dumke | gregory.michael | gneukum} @zedat.fu-berlin.de
"Institute of Photogrammetry and Geoinformation (IPI), Leibniz Universität Hannover, Nienburger Str. 1, 30167
Hannover, Germany - schmidt@ipi.uni-hannover.de
Commission IV, WG IV/7
KEY WORDS: Adjustment, Orientation, Block, Bundle, DEM/DTM, Mosaic, Orthoimage, Planetary
ABSTRACT:
The High Resolution Stereo Camera (HRSC) onboard the European Space Agency’s (ESA) Mars Express (MEX) has been orbiting
Mars since December 2003. One of the main aims is to cover Mars globally in color and stereoscopically at high resolution. HRSC
has so far covered almost half of the surface of Mars at a resolution better than 20 meters per pixel. High resolution digital terrain
models (DTM) are necessary for geoscientific studies of Mars. To get a more comprehensive view of regional processes on Mars,
images as well as topographic data have to be mosaicked photogrammetrically. This paper briefly describes the simultaneous
adjustment of exterior orientation for six HRSC orbit strips covering the Mawrth Vallis region, based on tie point matching and
bundle block adjustment as well as the derivation of a DTM mosaic with a ground resolution of 75 m per pixel and an ortho-image
mosaic with a ground resolution of 12.5 m per pixel.
1. INTRODUCTION
Since December 2003, the European Space Agency’s (ESA)
Mars Express (MEX) orbiter has been investigating Mars. The
High Resolution Stereo Camera (HRSC), one of the scientific
experiments onboard MEX, is a pushbroom stereo color
scanning instrument with nine line detectors, each equipped
with 5176 CCD sensor elements. Five CCD lines operate with
panchromatic filters and four lines with red, green, blue and
infrared filters at different observation angles (Neukum et al.
2004). MEX has a highly elliptical near-polar orbit and reaches
a distance of 270 km at periapsis. Ground resolution of image
data predominantly varies with respect to spacecraft altitude and
the chosen macro-pixel format. Usually, although not
exclusively, the nadir channel provides full resolution of up to
10 m per pixel, stereo-, photometryand color channels have
generally a coarser resolution. Furthermore, image data is
compressed onboard using a Discrete Cosine Transformation
(DCT) algorithm. One of the goals for MEX HRSC is to cover
Mars globally in color and stereoscopically at high resolution.
So far, HRSC has covered almost half of the surface of Mars at
a resolution better than 20 meters per pixel. Such data are
utilized to derive high resolution digital terrain models (DTM),
ortho-image mosaics and additional higher-level 3D data
products such as 3D-views (see Fig. 12).
Standardized high-resolution single-strip digital terrain models
(using improved orientation data) are derived at the German
Aerospace Center (DLR) in Berlin-Adlershof (Gwinner et al.
2008). Those datasets, i.e. high-resolution digital terrain models
as well as ortho-image data, are distributed as Vicar image files
(http://wwwmipl. jpl.nasa.gov/extemal/vicar.html) via the
HRSCview web-interface (Michael et al. 2008), accessible at
http://hrscview.fu-berlin.de. A systematic processing workflow
is described in detail in Scholten et al. (2005) and Gwinner et al.
(2005). For geoscience analysis and as part of a specific
agency-funded contribution from the Freie Universität,
multi-orbit DTMs as well as ortho-images are derived from
block-adjusted exterior orientation and will also be distributed
via the HRSCview web-interface as well as via the ESA
Planetary Archive (PSA) interface in the near future.
Geoscientific studies can be carried out in single-orbit image
data, but in order to obtain a more comprehensive view of
regional processes on Mars, images as well as topographic data
have to be mosaicked photogrammetrically. Until recently, the
only detailed information on the global topography was
provided by the Mars Orbiter Laser Altimeter (MOLA) which
operated between 1997 and 2001 onboard Mars Global
Surveyor (MGS) (Smith et al. 2001 and Neumann et al. 2003).
MOLA-based DTMs have a ground resolution of approximately
463 m per pixel and up to 231 m per pixel at the poles. The
accuracy of the DTM is 200 m in planimetry and 10 m in
height.
2. INPUT DATA
In consideration of the scientific interest, the processing of the
Mawrth Vallis region will be discussed in this paper. The
panchromatic ortho-image and DTM mosaic (see Fig. 11) was
derived from six HRSC orbits and covers an area of about 180
000 km2 at approximately 19.6° to 28° N and 333.5° to 340.5°
E. This is a relatively flat area with some large impact craters.
All six HRSC orbits have good image quality (low noise and
good contrast), a similar ground resolution (nadir channel) and
some overlapping areas. In addition, several of the off-nadir
panchromatic channels were acquired at full resolution (see
Table 1)
