PDS_VERSION_ID = PDS3 LABEL_REVISION_NOTE = "2015-12-15 K. Jha, original 2015-12-15 Neumann, data confidence note." RECORD_TYPE = STREAM OBJECT = DATA_SET DATA_SET_ID = "LRO-L-LOLA-3-RADR-V1.0" OBJECT = DATA_SET_INFORMATION DATA_SET_NAME = "LRO MOON LASER ALTIMETER 3 RADR V1.0" DATA_SET_COLLECTION_MEMBER_FLG = "N" DATA_OBJECT_TYPE = TABLE START_TIME = 2009-09-15T21:52:46 STOP_TIME = 2010-09-16T19:15:57 DATA_SET_RELEASE_DATE = 2015-12-15 PRODUCER_FULL_NAME = "DAVID E. SMITH" DETAILED_CATALOG_FLAG = "N" DATA_SET_TERSE_DESC = "Radiometry (albedo) science data from the nominal mission phases of the 2009 Lunar Reconnaissance Orbiter mission." CITATION_DESC = "Smith, D.E., 2009 Lunar Orbiter Laser Altimeter Radiometry Data Set, LRO-L-LOLA-3-RADR-V1.0, NASA Planetary Data System, 2015." ABSTRACT_DESC = " This data set contains archival radiometric data derived from reduced altimetry measured by the Lunar Orbiter Laser Altimeter instrument during LRO's Nominal Mission. LOLA is a pulse detection, time-of-flight laser altimeter that measures the distance between the LRO spacecraft and the surface of the Moon. LOLA transmits a 5-spot pattern, thus providing 5 simultaneous profiles across the lunar surface whose separation depends on spacecraft altitude. LOLA also measures the energy of the return pulses, which enables the calculation of the surface albedo after calibration." DATA_SET_DESC = " Data Set Overview ================= This data product is presented as along-track profiles that contain normal albedo, the radiance of the Moon at zero phase angle relative to a Lambert surface illuminated normally. Calculations are done as described in LEMELINETAL2016 using laser data collected during the thirteen Nominal Mission phases. Normal albedo has been corrected for the sensitivity drift of the laser with time, and for the loss of signal from temperature-dependent loss of alignment of the laser transmitter in the polar regions. Each TAB file contains data for a given LRO orbit, where each line corresponds to a laser return. The data is stored in 13 columns: latitude (degrees), longitude (degrees), normal albedo, Terrestrial Dynamic Time, laser used, detector used, reflectance (fraction), received energy (zJ), transmit energy (mJ), range (km), solar incidence angle (degrees), Off nadir angle (degrees), dropoff fit (fraction). These values, as well as their locations with each data file, are described in the accompanying LOLARADR.FMT file. Not every return with valid altimetry has a corresponding albedo value, as the energy measurement quality also depends on the solar incidence angle. The following conditions were applied to qualify pulses for inclusion in a data file: solar incidence angle lower than 90 degrees (daytime data), received energy greater than 0.14 zJ, a spacecraft off-nadir angle between 0.2 and 0.4 degrees, and an overall range lower than 70 km from the surface. The data acquired using Laser 1 and Laser 2 are archived in separate directories. Instabilities in passive Q-switched lasers cause strong variations in the transmitted energy. When normal albedo is calculated using data acquired by Laser 1, these anomalies are removed and yield proper normalization of the data for the transmitted energy variation. However, in the case of Laser 2 data, normalization leaves a residue of several percent positive anomalies near the boundaries of change in out-going laser pulse energy. The transmitted energy collected by LOLA when using Laser 2 may not be a full characterization of the out-going laser pulse energy. The normal albedo calculated using data from Laser 2 has substantially higher uncertainty than that using Laser 1. Data in the PolarPatch_NP and PolarPatch_SP folders contain normal albedo data acquired by Laser 1 at solar incidence angles greater than 90 degrees (nighttime data), which have been used to fill the gaps in coverage near the poles that occur when using day time data only. For the south polar region, nighttime data from orbits 4014-4264 (used in ZUBERETAL2012) were included between 85-90 degrees South. For the north polar region, nighttime data from orbits 4850-4971 and orbits 5318-5360 were included, between 87-90 degrees North. The nighttime normal albedo data have been scaled to the day time normal albedo from Laser 1 in overlapping regions. The data are stored in the following directory structure: DATA |--LOLA_RADR | |--LASER1 | | | |--LRO_[mission phase]_[orbital cycle] | | | | | |--LOLARADR_yydddhhmm.TAB | | | |--POLARPATCH_[NP or SP] | | | |--LRO_[mission_phase]_[orbital cycle] | | | |----LOLARADR_yydddhhmm_[NP or SP].TAB | |--LASER2 | |--LRO_[mission phase]_[orbital cycle] | |--LOLARADR_yydddhhmm.TAB Each data file is accompanied by a PDS label file with the same name, extension '.LBL'. " CONFIDENCE_LEVEL_NOTE = " Confidence Level Overview ========================= The active measurement of reflectance meets the requirements of the LRO mission to locate potential lunar resources and map them at ~25-400m scales in shadows where exposures of ice-regolith mixtures may be detected. The LOLA instrument implemented this measurement with an electronic energy measurement function that integrates and samples the peak of the amplified detector hybrid output with a track-and-hold function, followed by an 8-bit digitizer. The output of the digitizer is proportional to the energy for a given amplifier gain. Throughout the bulk of the mission the gain has been fixed at its maximum. The baseline of the digitized signal and constant of proportionality for each of the five receiver-detector-electronic systems were calibrated on the ground. The calibration parameters did not match the results obtained in flight, and an independent estimate of the baseline was derived by fitting the response as a function of range distance. A further estimate of the proportionality was derived from comparisons with imaging systems on other missions whose radiometric calibration was more precise than can be obtained with a pulsed system. The resulting energy measurement is limited to a range of 0.1 - 3 fJ at the detector. Its precision above 0.2 fJ is 12% until it reaches saturation, which occurs only rarely in flight. Likewise the transmitted energy was calibrated on the ground and its precision is nominally 2% when corrected for temperature response of the monitor. The accuracy of the transmit energy is affected by the proportion of the laser beam sampled which will inevitably change in flight as the beam shape changes with age. The scale factor of the measurement is affected by the optical system used to sample the beam by means of partial transmission and has increased with age. Thus the reflectance measurement in flight is limited in range and must be calibrated with empirical adjustments. Calibration Observations ======================== Observations of the LOLA laser and detector through the Earth's atmosphere have been performed in 2009 and 2014. Owing to the slews necessary to put the five laser spots within the field of view of the ground system and the operational difficulties of pointing the instrument deck away from the Moon it has only been possible to characterize the laser beam qualitatively and observe changes in its pattern that corroborate the reduction in output of each of the two lasers during limited time intervals. The atmosphere attenuates the energy as well in an unpredictable fashion. Thus the nominal instrument response is adjusted empirically. Lastly, the Earth observations have confirmed a misalignment of the laser beams with the detectors that is induced by thermal contraction when facing the cold night surface of the Moon or deep space. The transition from dayside to night changes the alignment and the portion of energy reaching the detector over the course of a few minutes on each orbit, and varies with the angle of the orbital plane with respect to the sun (beta angle). During the highest beta angle season that occurs semiannually the misalignment over the terminator is most severe and precludes measurements. Mission Phases and Intervals ========================= Observations are interrupted by monthly orbit trim maneuvers and data are broken into approximately monthly Phases during the LRO Nominal Mission. The energy measurements have a more limited range of availability than the altimetry and therefore depend strongly on altitude and laser output. Data Coverage and Quality ========================= The highest quality observations were obtained during the LOLA Nominal Mission Phases 01-13. Mission Phase Start Time (DOY) End Time (DOY) ------------- ---------------- -------------- LRO_NO_01 2009-258T21:00 2009-296T17:22 LRO_NO_02 2009-296T17:22 2009-324T16:00 LRO_NO_03 2009-324T16:00 2009-351T21:00 LRO_NO_04 2009-351T21:00 2010-013T19:00 LRO_NO_05 2010-013T19:00 2010-040T18:18 LRO_NO_06 2010-040T18:18 2010-068T17:24 LRO_NO_07 2010-068T17:24 2010-095T16:54 LRO_NO_08 2010-095T16:54 2010-123T15:59 LRO_NO_09 2010-123T15:59 2010-150T16:25 LRO_NO_10 2010-150T16:25 2010-178T17:15 LRO_NO_11 2010-178T17:15 2010-205T15:41 LRO_NO_12 2010-205T15:41 2010-232T12:18 LRO_NO_13 2010-232T12:18 2010-259T18:15 Some Science Mission and Extended Mission Phases have permitted more limited measurement of reflectance. Those data are not currently part of this dataset. Limitations =========== The precision of individual spot measurements is limited and averaging of data along track with exclusion of weaker or inconsistent measurements is required to map the observations to the lunar terrain." END_OBJECT = DATA_SET_INFORMATION OBJECT = DATA_SET_MISSION MISSION_NAME = "LUNAR RECONNAISSANCE ORBITER" END_OBJECT = DATA_SET_MISSION OBJECT = DATA_SET_TARGET TARGET_NAME = "MOON" END_OBJECT = DATA_SET_TARGET OBJECT = DATA_SET_HOST INSTRUMENT_HOST_ID = LRO INSTRUMENT_ID = "LOLA" END_OBJECT = DATA_SET_HOST OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "LEMELINETAL2016" END_OBJECT = DATA_SET_REFERENCE_INFORMATION END_OBJECT = DATA_SET END