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TOPOGRAPHIC MAPPING OF THE MOON 
M.T. Zuber 
Department of Earth, Atmospheric and Planetary Sciences 
Massachusetts Institute of Technology 
Cambridge, MA 02139-4307 
USA 
D.E. Smith 
Laboratory for Terrestrial Physics 
Code 920 
NASA/Goddard Space Flight Center 
Greenbelt, MD 20771 
USA 
Commision IV, Working Group 5 
KEY WORDS: DEM/DTM, extraterrestrial, mapping, electro-optical 
ABSTRACT 
We have processed laser altimetric data from the Clementine LIDAR to produce an accurate global model for the shape of 
the Moon. Ranges from the spacecraft to the lunar surface were converted to center of mass-referenced radii and expanded 
into a 72nd degree and order spherical harmonic model for lunar topography. Results show that the present shape of the 
Moon is a sphere with maximum positive and negative deviat 
Korolev and South Pole-Aitken basins. The near side has a gent 
ions of ~8 km, both occurring on the far in the areas of the 
le topography with an rms deviation of only about 1.4 km with 
respect to the best-fit sphere compared to the far side. The shapes of the histograms of the deviations from the sphere show 
a peaked distribution slightly skewed toward lower values for the near side, while the far side is broader but shows the South 
Pole-Aitken Basin as an anomaly compared to the rest of the hemisphere. Where Apollo and Clementine altimetry coverage 
overlap, measured relative topographic heights generally agree to within ~ 200 m, with most of the difference due to our more 
accurate orbit corrections for Clementine and to variations in large-scale urface roughness. 
1 BACKGROUND 
1.1 The Clementine Mission 
The Clementine Mission, sponsored by the Ballistic Missile 
Defense Organization with science activities supported by 
NASA, mapped the Moon from February 19 through May 
3, 1994 (Nozette et al. 1994). The spacecraft included a 
Light Detection and Ranging (LIDAR) instrument that was 
built by Lawrence Livermore National Laboratory (Nozette et 
al. 1994). While the spacecraft was in orbit, this instrument 
was operated as a ranging device and collected near-globally 
distributed profiles of elevation round the Moon (Zuber et al. 
1994). In this paper we discuss how data from the lemen- 
tine LIDAR were processed to yield a global, geodetically- 
referenced model for the topography of the Moon. 
1.2 Pre-Clementine Measurements of Lunar Topogra- 
phy 
Measurements of lunar elevation have been derived from 
Earth-based and orbital observations. Earth-based measure- 
ments of lunar topography have necessarily been limited 
to the near side, and include limb profiles (Watts 1963), 
ground-based photogrammetry (Baldwin 1963; Hopmann 
1967; Arthur and Bates 1968; Mills and Sudbury 1968) and 
radar interferometry (Zisk 1971; Zisk 1972). These studies 
yielded information of limited spatial distribution and posi- 
tional knowledge of order 500 m. 
Orbital data include landmark tracking by the Apollo com- 
mand and service modules (Wollenhaupt et al. 1972), profil- 
ing by the Apollo long wavelength radar sounder (Brown et 
al. 1974), limb profiles from the Zond-6 orbiter (Rodionov 
et al. 1971) and photogrammetry from the Lunar Orbiters 
(Jones 1973). None of these observations was selenodeti- 
cally referenced to the Moons center-of-mass, and all were 
characterized by absolute errors on the order of 500 m. 
More accurate lunar shape information was derived from or- 
bital laser ranging. The Apollo 15, 16 and 17 missions carried 
laser altimeters which provided measurements of the height 
of the command modules above the lunar surface (Kaula et 
al. 1972: Kaula et al. 1973; Kaula et al. 1974). These 
measurements provided the first information on the shape of 
the Moon in a center of mass reference frame. 
2 LUNAR TOPOGRAPHIC MODEL 
2.1 Measuring Lunar Topography 
The Clementine LIDAR measured the slant range of the 
spacecraft to the lunar surface at spacecraft altitudes of 640 
km or less. The instrument collected data for approximately 
one-half hour per 5-hour orbit for the two month lunar map- 
ping mission. Specifications for the instrument are given in 
Table 1. For the first month, with spacecraft periselene at 
latitude —30?, topographic profiles were obtained in the ap- 
proximate latitude range —79° to +22°, while in the sec- 
ond month of mapping, with spacecraft periselene at latitude 
+30°, profiles were obtained in the approximate range —20° 
to +81°. 
To produce a global topographic dataset from the lidar sys- 
tem it was first necessary to subtract from the range profiles 
a precise orbit. We computed these orbits with the GEO- 
DYN/SOLVE orbital analysis programs (Putney 1977; Mc- 
Carthy et al. 1994). We interpolated the spacecraft orbital 
trajectory to the time of the laser measurement, and then ac- 
1011 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996