THE TOPOGRAPHY OF LUNAR IMPACT BASINS AS DETERMINED FROM 
RECENTLY OBTAINED SPACECRAFT STEREO IMAGES 
J. Oberst, W. Zhang, M. Wählisch, A.C. Cook, T. Roatsch, R. Jaumann 
DLR, Institute of Planetary Exploration, 12489 Berlin, Germany 
Commission IV, Working Group 5 
KEYWORDS: DEM/DTM, Stereoscopic, Extraterrestrial, Mapping, Imagery 
ABSTRACT 
We analyzed images obtained during the Galileo flyby in 1992 and by the Clementine orbiter in 1994 to derive Digital Terrain 
Models (DTM) of selected large lunar impact basins, in particular, the Humboldtianum basin, Mare Crisium, and parts of Mare 
Orientale. The Humboldtianum terrain model has a lateral resolution of 2 km/pixel and a height resolution of 500m. In the Orientale 
area we processed stereo images along a narrow strip cross-cutting the Rook and Cordillera Rings of the basin, and derived a terrain 
model with grid spacing of 200 m/pixel and height resolution of 50m. The new topographic data exceed the Clementine laser 
altimeter data in terms of resolution and noise level and will allow us to carry out morphological studies of the lunar impact basins in 
unprecedented detail. 
1. INTRODUCTION 
The large impact basins are important landmarks in lunar 
geology and morphology. The multiple rings associated with 
these basins represent the major lunar mountain ranges. The 
basin floors form deep regional depressions and often contain 
large volumes of volcanic deposits. However, the dynamics of 
formation of these basins and their evolution through lunar 
history has been an enigma, partially because information on 
their topography has been very poor. Previous studies of lunar 
topography included shadow-length measurements of mountain 
peaks (Jones, 1965), limb profiling (Watts, 1963; Appleby and 
Morrison, 1983), radar mapping from Earth (Zisk, 1972; Zisk et 
al., 1974), and analysis of Apollo Metric stereo images (Wu and 
Doyle, 1990; Cook et al., 1994) in the nearside equatorial 
regions. 
Fortunately, our prospects to refine lunar topography have 
significantly improved in the past years. The Galileo and 
Clementine spacecraft encountered the Moon and obtained a 
wealth of digital stereo image data. These data provide the 
opportunity to derive Digital Terrain Models (DTMs) with high 
lateral resolutions using state-of-the-art photogrammetric 
methods of analysis. In addition, during the Clementine 
mission, for the first time ever, laser altimeter data were 
collected for studies of the global lunar shape. 
In this paper we will describe the spacecraft image data, 
photogrammetric methods of analysis, and the properties of the 
resulting terrain models. Finally, models are compared with 
those from laser altimetry. We discuss the advantages and 
disadvantages of using either stereo images or laser altimetry 
for studies of lunar topography. 
2. SPACECRAFT STEREO IMAGES 
Galileo passed the Moon on December 7, 1992 at a distance of 
110,000 km. Approximately 300 multi-look-angle images of 
the near-side northern lunar hemisphere were obtained by the 
SSI (Solid State Imaging) camera (Table 1) showing the 
Humboldtianum basin (82°E, 57°N) and Mare Crisium (58°E, 
18°N) at image scales of approximately 1 km/pixel. 
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In contrast, the Clementine spacecraft orbited the Moon from 
February through May 1994, at altitudes ranging from 400 - 
2940 km and gathered nearly 2 million images. Whilst the 
majority of the data were obtained with the cameras pointed 
towards nadir for global mapping, there were specific imaging 
sequences near the end of the mission during which the 
spacecraft was tilted to obtain stereo data (Cook et al., 1996). 
Excellent stereo coverage was obtained by the UVVIS camera 
(Table 1) near Mare Orientale, located on the western lunar 
limb (20°S, 89°W). Ground pixel sizes in the area were 
approximately 100-150 m/pixel. 
Table 1: Cameras 
  
Galileo SSI ~~ Clementine UV VIS 
CCD chip size 800x800 384x288 
focal length (mm) 1500 90 
pix scale (px/mm) 65.617 43.478 
  
Due to the large number of images involved, deriving terrain 
models of the entire Orientale Basin would have been a very 
time-consuming task. Instead, we selected a linear profile 
cross-cutting the Inner Rook, Outer Rook, and the Cordillera 
Rings near the eastern margin of the basin, along which we 
modelled topography. The input image data consist of 43 nadir- 
pointed images obtained from orbit 333 and a second set of 53 
tilted images obtained a few hours later (orbits 334, and 338) 
under similar lighting conditions. Although multispectral data 
are available from the Clementine and Galileo cameras, only 
single-filter images, respectively, were used in the analysis. 
3. STEREO PROCESSING 
For both, Galileo and Clementine, the photogrammetric 
processing was carried out using similar methods (Oberst et al., 
1996). First, the nominal spacecraft trajectory and camera 
pointing information supplied by the Galileo and Clementine 
flight projects were adjusted using hand-picked line/sample 
coordinates of conjugate points or ground control points (Zhang 
et al., 1996). 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996