International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B4, 2012
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia
DIGITAL ELEVATION MODELS AND DERIVED PRODUCTS FROM LROC NAC
STEREO OBSERVATIONS
K.N. Burns“, E.J. Speyerer“, M.S. Robinson“, T. Tran“, M.R. Rosiek®, B. A. Archinal®, E. Howington-Kraus® and the
LROC Science Team
* School of Earth and Space Exploration, Arizona State University, 1100 S Cady, Tempe AZ 85287 —
(knburns1@asu.edu)
? Astrogeology Science Center, United States Geological Survey, 2255 N Gemini Dr, Flagstaff AZ 86001 —(mrosick
>
barchinal, ahowington)@usgs.gov
Commission IV, WG IV/7
KEY WORDS: DEM/DTM, Three-dimensional, Application, Planetary, Mapping, Geomorphology, Modeling, Processing
ABSTRACT:
One of the primary objectives of the Lunar Reconnaissance Orbiter Camera (LROC) is to acquire stereo observations with the
Narrow Angle Camera (NAC) to enable production of high resolution digital elevation models (DEMs). This work describes the
processes and techniques used in reducing the NAC stereo observations to DEMs through a combination of USGS integrated
Software for Imagers and Spectrometers (ISIS) and SOCET SET® from BAE Systems by a team at Arizona State University (ASU).
LROC Science Operations Center personnel have thus far reduced 130 stereo observations to DEMs of more than 130 stereo pairs
for 11 Constellation Program (CxP) sites and 53 other regions of scientific interest. The NAC DEM spatial sampling is typically 2
meters, and the vertical precision is 1-2 meters. Such high resolution provides the three-dimensional view of the lunar surface
required for site selection, hazard avoidance and planning traverses that minimize resource consumption. In addition to exploration
analysis, geologists can measure parameters such as elevation, slope, and volume to place constraints on composition and geologic
history. The NAC DEMs are released and archived through NASA's Planetary Data System.
1. INTRODUCTION
1.1 LROC
The Lunar Reconnaissance Orbiter Camera (LROC) consists of
two narrow angle cameras (NACs) to provide 0.5 — 2.0 meter-
scale panchromatic images of a Skm swath and a wide-angle
camera (WAC) to provide images at a pixel-scale of 100 meters
in seven color bands over a 60km swath (Robinson et al. 2010).
The NAC was not designed as a stereo system, but obtains
stereo pairs through images acquired from two orbits, with the
spacecraft making at least one off-nadir slew (Figure 1). Stereo
observations are nominally obtained on consecutive orbits in
order to minimize lighting changes between observations.
Slewing the spacecraft off-nadir interferes with data collection
from other instruments, so LROC slew opportunities are limited
to four per 24 hour period. Slew angles range between 0° and
30° and a convergence angle between images is typically
between 10° and 45°.
1.2 DEM Production
This paper describes the production and release of NAC DEMs
produced by the ASU team. However, NAC DEM production
is carried out at various other institutions affiliated with the
LROC team, including U.S. Geological Survey (USGS), NASA
Ames, Jet Propulsion Laboratory (JPL), University of Arizona
(UA), Ohio State University (OSU), and the German Aerospace
Center (DLR) (Cohen et al. 2008). ASU, USGS, NASA Ames,
and UA all use SOCET SET from BAE Systems (DeVenecia et
al. 2007) for photogrammetric processing of NAC images.
NASA Ames is using their Stereo Pipeline (Moratto et al. 2010)
and OSU is using their Orbital Mapper and Leica
Photogrammetry Suite 9.3. DLR uses photogrammetry software
developed in-house (Oberst et al. 2010).
2. DATA SOURCES
Figure 1. Diagram Illustrating NAC stereo image acquisition.
2.1 LROC NAC
The LROC NACs are linear pushbroom cameras built using the
Kodak KLI-5001G line array. The line array is a 5064 element
charge coupled device (CCD) with 7-micron pixels. The two
NAC cameras are designated NAC-Left (NAC-L) and NAC-
Right (NAC-R). The NACs are mounted on the spacecraft such
that the CCDs are perpendicular to the spacecraft’s X-axis.
Each camera is designed to provide 0.5 meter pixel scale
panchromatic images covering a 2.5 km swath cross-track, for a
combined coverage of 5 km, at an altitude of 50 km. Each
camera has an internal buffer of 256MB; allowing for an Image
length of 52,224 lines or 26,112 meters at the native resolution.
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