International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B4. Istanbul 2004
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Fig. 3: Screen shot showing small sections of the HRSC scene (left: nadir, center: stereol, right: stereo2) from orbit 18 and
conjugate points identified by HWMATCHI.
by-shot along tracks, with spacings of approx. 300 m on the
ground. While the data coverage is quite dense near the
poles (MGS was in a polar orbit), there is a spacing of the
MOLA tracks of several kilometers near the equator.
Contiguous terrain models are obtained by interpolation.
Owing to the considerable laser surface spot size of approx.
i] 160 m, the measurements involve some averaging over a x
| patch. The relative or absolute height accuracy of individual Fig. 5: La
| MOLA shots was estimated to be better than 50 cm or 1.5 m, this model
respectively (Smith et al., 2001; Neumann et al., 2003). p4 extract
We derived a HRSC-DEM with an effective resolution of 300
m per grid pixel (Fig. 5), specifically for a comparison with
the available MOLA gridded model, which was originally
à ROMPE interpolated from MOLA tracks (which typically run in the
North/South direction). Note that 300m corresponds to
MOLA’s shot-to-shot spacing. Four different profiles were
—40 —20 0 20 40 placed across the DEM. The profiles pl-p3 are oriented
gcross—track distance, m exactly along MOLA tracks, while p4 is purposely placed
across the MOLA tracks.
—20
along-track distance, m
The SRC
intended
context of
from orbit
SRC imag
reference
mosaicked
pointing d;
location w
across-trac
(presumab
between tl
the SRC ai
Fig. 4: Ray intersection points with the surface for rays
from the nadir (blue), the stereol (red), and the stereo 2
(green) channel. 97% of the rays meet within a sphere of
radius 20m.
The stereo and laser altimeter terrain models show excellent
agreement. The differences in absolute heights are on the
order of 50 m only and horizontal offsets are about 100 m
for this orbit. These minor offsets are to be removed by
bundle block adjustment techniques (Ebner et al., 2004).
= 7
5. COMPARISON WITH MOLA Judging from the profiles pl, p2, and p3, the HRSC terrain
model of 300m scale shows details at a level similar to the
The Mars Orbiter Laser Altimeter (MOLA) on board the Mars MOTA e Fons ds Tig we K p thc SRC imag
Global Surveyor (MGS) has completed its mapping of the resolutions ol. the HASC: models Tor more detau. d de ded
across-track direction, our stereo terrain model already
planet in June 2001. MOLA data have practically redefined
the Mars-coordinate system and established a new reference
surface for the planet. Therefore, a comparison of our stereo-
derived terrain data with MOLA models provides an
excellent test for accuracy of the HRSC within the Mars-
fixed coordinate system. The MOLA data are obtained shot-
exceeds the spatial resolution of the MOLA models (see
profile p4), suggesting that HRSC conveniently fills gaps in
the coverage left by MOLA.
