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at local to regional scales panchromatically and in four
narrow-band colors, and the WAOSS designed for global
coverage and for panchromatic observations of time-
dependent phenomena. The unique advantage over pre-
vious imaging experiments from Mars orbits is in the
simultaneous stereo, spectral, and photometric coverage by
combined operation of the two sensors. For some technical
parameters see Table 1.
Parameter HRSC WAOSS
Focal length 175 mm 21.7 mm
Number of CCD lines 9 3
Active pixels/CCD line 5184 5184
Radiometric resolution:
A/D converter bits 10 bit 11 bit
Bits entering compression 8 bit 8 bit
Field of view 11:99 80.0?
Stereo angle (convergence) 18.9? 25.3?
Swath width* 62 km 519 km
Maximum ground resolution* 12m 97m
Weight 24 kg 7 kg
* for flying altitude 300 km at the pericenter
Table 1: Technical parameters of HRSC and WAOSS
Both instrument designs benefit from the experience gained
from previous three-line stereo cameras and hybrid tech-
nology electronics. Thus, both cameras use multiple CCD
line detectors mounted in parallel. These CCD sensors are
installed on focal plate modules which are almost identical
for both cameras. Modern high-reliability hybrid technology
has permitted the incorporation of miniaturized sensor
electronics.
2.1 High Resolution Stereo Camera (HRSC)
The HRSC instrument is a high resolution CCD scanner with
nine CCD lines providing multiple along-track stereo imagery
as well as colour information and high resolution image data
(up to 12 m/pixel). It was designed at DLR and the main
contractor for its production is the Dornier company in Fried-
richshafen, Germany. HRSC is optimized for local and re-
gional coverage of preselected surface areas. Typically,
Fig. 1: General view of the High Resolution Stereo
Camera (HRSC)
59
image strips of more than 300 km length will be collected.
These strips will be recorded as overlapping data takes by
9 separate sensors (3 panchromatic stereo sensors, 4
multispectral sensors, and 2 additional photometric sensors).
After ground data processing, the image data will yield high
resolution, stereo capability, and thematic information.
The imaging parameters for each exposure sequence have
to be commanded in advance. Owing to the different viewing
angles of the individual sensors within the HRSC focal pla-
ne, the sensor data have to be activated and deactivated
sequentially to obtain overlapping ground coverage. In
addition, the sensor exposure times have to be adapted to
the varying spacecraft velocities and heights along the
elliptical orbit.
2.2 Wide Angle Optoelectronic Stereo Scanner (WAOSS)
WAOSS was designed for wide angle scanning of the
Martian surface and atmosphere. Three CCD line sensors
provide panchromatic wide angle stereo coverage. WAOSS
permits on-line adaptation of sensor exposure times, signal
level normalization, pixel binning and compression rates. In
contrast to the multi-box concept of HRSC, WAOSS was
conceived as a compact single box instrument with inte-
grated baffle, optics, spectral filters, power convertér, 3 CCD
line sensors, sensor electronics, and a digital unit for
interfacing, data handling, image data preprocessing and
compression.
The wide angle conception of WAOSS with its three CCD
lines again enables along-track stereo capability but with a
much larger field of view. Thus global coverage of the planet
Mars with a ground pixel size of 100 m/pixel and larger can
be realized.
2.3 Camera Calibration and Tests
The design goals, in particular photogrammetry and spectro-
photometry, impose strong requirements on the geometric
and radiometric precision ot the two camera systems.
Therefore, a thorough calibration of the different flight models
of the two camera systems was started in 1994. The
calibrations are being conducted in three stages, the pre-
calibration of the focal plate subunit, the radiometric
calibration of the camera head (which includes the optical
system), and the geometric calibration of the camera head.
Calibrations for HRSC were done at the DLR Ober-
pfaffenhofen facility and the Dornier laboratory in Friedrichs-
hafen. WAOSS is being calibrated at the DLR-Berlin-Adlers-
hof facility.
Outdoor tests of the cameras were conducted in spring 1995
to verify proper combined operations of both cameras and
to test their imaging performance. Both cameras were
installed on a turn-table which was rotated at a rate that
matched the scan rate of the cameras to simulate spacecraft
motion. The first images were obtained from the Dornier
campus near Friedrichshafen with viewing across Lake
Constance and the Swiss Alpes near the Sántis mountain
(Fig. 2). The image data of HRSC and WAOSS were com-
pressed in such a way that compression factors of ap-
proximately 5 - 8 were normally achieved. However, higher
compression rates of up to 40 were also achieved to allow a
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996
