Data Set Information
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| DATA_SET_NAME |
CLEM1 LIDAR TOPOGRAPHY V1.0
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| DATA_SET_ID |
CLEM1-L-LIDAR-3-TOPO-V1.0
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| NSSDC_DATA_SET_ID |
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| DATA_SET_TERSE_DESCRIPTION |
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| DATA_SET_DESCRIPTION |
Data Set Overview: The Clementine spacecraft included a Light Imaging Detection and Ranging (LIDAR) instrument. The LIDAR instrument measured the slant range from the spacecraft to the lunar surface. The instrument acquired high resolution profiles of lunar topography. This data set contains aggregated topographic ranges, radii, and related data along each observational pass during which LIDAR laser range data were acquired. The data were created using preliminary spacecraft timing, orientation, and orbital solutions. The laser ranges have been converted from counts to meters using a calibration factor of 39.972 m per count. Timing information may have substantial errors owing to spacecraft computer resets and clock ambiguity. The lidar electronics triggered on photon pulses continuously, and recorded up to four pulses within a programmable range window. The last trigger before and the first trigger after the range window were also recorded. Usually, but not always, the first trigger within the range window was the valid range. For a few laser shots, multiple pulses were detected within the expected time interval for lunar reflections. Note: the fields START_ORBIT_NUMBER and STOP_ORBIT_NUMBER in the product labels refer to the Clementine revolution numbers, which increment at the start of the observational pass.Parameters: The LIDAR instrument measured the slant range from the spacecraft to the lunar surface at spacecraft altitudes of 640 km or less. Range value was determined by the number of clock cycles between the laser start pulse and the received signal. The spacecraft orbited within ranging distance (orbital altitudes less than 640 km) for approximately one-half hour per 5-hour orbit during the 2-month lunar mapping mission, and typically ranged at a rate of 1 shot per 1.6 seconds. The elevations, in meters, were referenced to a spheroid with flattening of 1/3234.93.Processing: Range was determined by the number of clock cycles between the laser start pulse and returned signal, using a calibration factor of 39.972 m per cycle. Determining the range involved interpolating the spacecraft orbital trajectory to the time of the laser measurement, applying time-tag corrections to the original lidar data as supplied by the Naval Research Laboratory, including a 2 msec delay to the laser fire time. Corrections were then made for the one-way light time to the surface, and the measured range from the spacecraft to the surface was then transformed to a lunar radius in a center-of-mass reference frame. Lunar radii are thus expressed in selenocentric surface coordinates. The spacecraft quaternions were then used to correct the ranges for off-nadir pointing of the spacecraft. During the course of the mission the LIDAR typically ranged at a rate of 1 shot per 1.6 seconds and triggered on about 123,000 shots, corresponding to 19% of the transmitted laser pulses. Typical along-track shot spacings were on the order of 20 km, but this varied considerably. Ranging at 8 Hz was performed on pass 323 and successfully downloaded. Much of the time, the first trigger in the range window was a true echo, but often, particularly over rough terrain, there were multiple triggers that did not correlate with lunar features. This data set was used to create the digital topographic model of the Moon, PDS data set CLEM1-L-LIDAR-5-TOPO-V1.0. See the documentation for that data set for more information.
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| DATA_SET_RELEASE_DATE |
2007-01-01T00:00:00.000Z
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| START_TIME |
1994-02-21T10:06:27.192Z
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| STOP_TIME |
1994-03-12T07:07:28.591Z
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| MISSION_NAME |
DEEP SPACE PROGRAM SCIENCE EXPERIMENT
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| MISSION_START_DATE |
1991-11-19T12:00:00.000Z
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| MISSION_STOP_DATE |
1994-05-07T12:00:00.000Z
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| TARGET_NAME |
MOON
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| TARGET_TYPE |
SATELLITE
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| INSTRUMENT_HOST_ID |
CLEM1
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| INSTRUMENT_NAME |
LASER RANGEFINDER
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| INSTRUMENT_ID |
LIDAR
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| INSTRUMENT_TYPE |
ALTIMETER
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| NODE_NAME |
Geosciences
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| ARCHIVE_STATUS |
SUPERSEDED
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| CONFIDENCE_LEVEL_NOTE |
Overview: Orbits were characterized by a formal uncertainty in radial position of about 10 meters and have an accuracy with respect to the lunar center of mass of approximately 100 m [LEMOINEETAL1995], which is comparable to the single-shot ranging precision of the lidar (40 m).Data Coverage/Quality: Laser ranging was performed on revolutions 8 to 163 in the southern hemisphere during the first month, and revolutions 165 to 332 in the north during the second month of the mapping phase of the mission. During the first month, with spacecraft periselene at latitude -30 degrees, topographic profiles were obtained in the approximate latitude range -79 to +20 degrees. In the second month of mapping, with spacecraft periselene at latitude +30 degrees, profiles were obtained in the approximate latitude range -20 to +82 degrees. This resulted in near-globally distributed profiles of elevation around the Moon [ZUBERETAL1994].
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| CITATION_DESCRIPTION |
Neumann, G., Clementine LIDAR Topography, CLEM1-L-LIDAR-3-TOPO-V1.0, NASA Planetary Data System, 2007.
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| ABSTRACT_TEXT |
This data set contains aggregated topographic ranges, radii, and related data along each observational pass during which Clementine LIDAR laser range data were acquired. The data were created using preliminary spacecraft timing, orientation, and orbital solutions. The laser ranges have been converted from counts to meters using a calibration factor of 39.972 m per count. Timing information may have substantial errors owing to spacecraft computer resets and clock ambiguity. The lidar electronics triggered on photon pulses continuously, and recorded up to four pulses within a programmable range window. The last trigger before and the first trigger after the range window were also recorded. Usually, but not always, the first trigger within the range window was the valid range. For a few laser shots, multiple pulses were detected within the expected time interval for lunar reflections.
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| PRODUCER_FULL_NAME |
DAVID E. SMITH
MARIA T. ZUBER
GREGORY A. NEUMANN
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| SEARCH/ACCESS DATA |
Clementine Data Archives
Geosciences Online Archives
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