Data Set Information
DATA_SET_NAME LRO LUNAR EXPLORATION NEUTRON DETECTOR 4/5 RDR V1.0
DATA_SET_ID LRO-L-LEND-4/5-RDR-V1.0
NSSDC_DATA_SET_ID
DATA_SET_TERSE_DESCRIPTION
DATA_SET_DESCRIPTION Data Set Overview : The Lunar Reconnaissance Orbiter (LRO) Lunar Exploration Neutron Detector (LEND) that will act as large orbital neutron telescope for mapping the Moon's neutron albedo. LEND consists of eight 3He sensors for detecting thermal and epithermal neutrons, four of which are collimated to improve spatial resolution. LEND also contains the Sensor for High Energy Neutrons (SHEN), which is a stilbene scintillator that produces a flash of light each time a high energy neutron in the energy range 0.3 - 15.0 MeV collides with a hydrogen nucleus and creates a recoil proton. A full description of the LRO LEND instrument can be found in [MITROFANOVETAL2008]. The LRO LUNAR EXPLORATION NEUTRON DETECTOR 4/5 RDR data set is a time series collection of rectified science data (RSCI), converted housekeeping data (CHK), derived science data (DLD), extended derived science data (DLX) and averaged science data (ALD). LEND collects a new spectrum (frame) approximately every second. Approximately 86400 spectra are expected to be received every day. The collection interval can be changed in the middle of a time series file, which can be determined by noting the difference between record timestamps. The data (both science and housekeeping) are downloaded from the spacecraft. Data are output to a spooler that passes them to the University of Arizona (UA) database ingest process. The ingest process inputs raw data into the UA database. Data are retrieved from the UA database to build the LEND RDR data products. The LEND RDR data set is intended to provide both intermediate (RSCI, CHK) and advanced (DLD, DLX, ALD) data products for the LEND instrument. This data should be useful to those scientists who are experienced in neutron spectroscopy. Parameters : The LEND RDR data set is composed of five data types, rectified science data (RSCI), converted housekeeping data (CHK), derived science data (DLD), extended derived science data (DLX) and averaged science data (ALD). The RSCI data type is the LEND science data with timing and spatial information added. The CHK data is the housekeeping data converted from digital number (as sent down from the spacecraft) to physical units. The DLD data type is a time series of science data for each of the nine LEND sensors that has been corrected for changes in detector efficiency and changes in the Cosmic Ray flux. In addition, records corrupted by Solar Particle Events and known instrument anomalies have been removed. The DLX data type is an extension of the DLD data type, containing supplemental values useful for interpretation of DLD data. The ALD data type takes the DLD data and averages it over a spatial and temporal grid as defined below. Processing : A full description of the LEND data processing can be found in the RDR SIS located in the document folder that accompanies this release. The following paragraphs are a summary of how the data are processed from data receipt through averaging. LEND data are downloaded from the LRO spacecraft. The data are received by a process called LEND_tl that translates LEND packets from any source to any destination and examines instrument health via messages. The data are checked for packet type, header information, messages, or errors, and are output to a spooler and to a data display IDL program called LEND Displays Data sent to the spooler are passed to the UA database ingestion process, which inputs raw data into the UA database. Data sent to the LEND Displays program is recorded at IKI and held in a data repository. All data packets received by the LEND Displays program are processed for timing and spatial information. Once time data are extracted from the data packet, UTC time is calculated from the spacecraft time (time at the middle of the collection interval) by a SPICE function. The UTC time is then inserted into the database. The spatial portion of the data packet is calculated using other SPICE routines. The returned values are all the spatial elements of an observation, including latitude and longitude at the mid-point of the observation. The RSCI data are output once timing and spatial elements are calculated for each collection interval in a given day. The LEND housekeeping data is also ingested into the LEND relational database. Upon ingestion, database triggers are used to convert digital numbers in the housekeeping data into physical units. The CHK data is the converted housekeeping data and also includes the UTC time at the mid-point of the collection interval. The LEND instrument collects 11 neutron signals from nine independent detectors, whose response functions are sensitive to different energy regions. Raw neutron counts are reported in the LEND RCSI data set as a 16-channel spectrum for each of the eight 3He detectors (SETN, CSETN1, CSETN2, CSETN3, CSETN4, STN1, STN2, and STN3) and as 3 spectra for the stilbene detector (SHEN_Low, SHEN_gamma and SHEN_High). In the DLD data set, neutron counts for the 3He detectors are reported as the sum of counts in channels 9-16, corrected for detector efficiency and Cosmic Ray flux. The counts for the omnidirectional detectors (SETN, STN1, STN2, and STN3) have also been normalized to a 50km altitude. The stilbene scintillator records two neutron signals and a gamma signal. The neutron counts are reported as the sum of counts in channels 9 and above for each of the signals. As of Release 25, March 15, 2016, the complete DLD data set was redelivered, reflecting updated normalization procedures for generating the DLD data set. The LEND DLD data set is generated from the rectified science (RSCI) data set, following normalization to correct for various effects. The data are normalized to correct for changes in count rate over time due to solar cycle cosmic-ray variations and any possible change in detector efficiency. The data are also corrected for differences in efficiency between each of the detectors. The normalization values are determined by separately averaging the counts in each of the detectors measured early in the mission over the polar regions (poleward of 60 degrees). The background term reported for each collection interval is the galactic cosmic-ray flux induced background as measured in each detector during the cruise phase of the mission when the spacecraft was far from both the Earth and the Moon. The observed background count for the detector of interest must be multiplied by (1-omega(t)/4pi) where omega(t) is the solid angle subtended by Moon for the current position in the spacecraft orbit. The resulting term is the background counts in the particular collection interval for the detector of interest. Background subtracted count values for each of the eleven neutron signals (SETN, CSETN1, CSETN2, CSETN3, CSETN4, STN1, STN2, STN3, SHEN_Low, SHEN_gamma, and SHEN_High) are temporally and spatially binned to create the ALD data. This data is used to compare seasonal and geographic changes in the neutron flux. The temporal binning is synodic periods and the spatial binning is half degree cells above and below 80, -80 degrees and one degree cells elsewhere. Membership in a temporal bin is determined by calculating the fraction of the collection interval time spent in each temporal cell. Membership in a spatial bin is determined by calculating the fraction of the collection interval length in a given spatial cell along the orbital trajectory projection on the Lunar surface. The temporally and spatially binned counts for each of the eleven signals are calculated by: 1) multiplying the background subtracted counts by the collection interval fraction and summing the result for each collection interval within the temporal interval 2) multiplying the duration (in seconds) of each collection interval by the collection interval faction and summing the result for each collection interval within the temporal interval 3) dividing the summed counts by the summed time to yield a counting rate in units of counts per second. The summed time is the EXPOSURE. The averaged counting rates are then normalized by the average counting rate from the region of the Moon defined as above. The normalization values for each signal are the *_NORMALIZATION fields given in the ALD data set. The normalization calculation yields the *_RATE fields, which can be used to create signal specific neutron maps. Because the rates are ratios of counting rates, they are unitless. Error fields, *_ERR, are also present for each of the signals. The errors are simply based on the counting statistics for the raw LEND counts. The conversion of normalized counting rates to neutron fluxes requires knowledge of the efficiency of each of the neutron detectors. Efficiency functions, derived from model calculations and direct calibrations, describe the directional and energy dependent response of each of the nine LEND detectors to bombardment by neutrons. A series of Monte-Carlo simulations will be run to calculate the efficiency of each LEND detector. The simulations will account for the composition and geometry of the LEND instrument. In parallel, a series of experimental calibration measurements will be carried out to understand the quality of the Monte-Carlo simulations. Two types of experiments will be performed. The first experiment measures the LEND response to monoenergetic neutron sources with known spectra and the second measures the LEND response to energetic neutron fluxes. The combined results of the numerical simulations and the experiments yield detector specific efficiency functions. As a further analysis of the data, calculations will be made with MCNPX for various models of the Moon. The neutron flux at the spacecraft predicted by these calculations will be fitted with a power law, AE^-alpha. The power law spectrum is then multiplied by the nine efficiency functions to obtain computed counting rates in the LEND detectors. These computed counting rates are compared to the real counting rates in via a Pearson minimizing procedure. The values, A and alpha, for the model that best satisfy the minimization criterion, are inserted into the ALD as the NEUTRON_NORM and ALPHA fields. The NEUTRON_NORM and ALPHA values are used to estimate the neutron flux (n/(cm^2-s)) at the LRO orbit in different ranges of epithermal and fast neutrons (EPITHERMAL_FLUX1 100 eV - 10 KeV, EPITHERMAL_FLUX2 10 KeV - 1 MeV, FAST_FLUX1 1 MeV - 2.5MeV, and FAST_FLUX_2 2.5 MeV - 10 MeV) for each map grid by taking the integral of the neutron spectrum as described by A and alpha over the energy interval. See the RDR SIS located in the Documents directory that accompanies this release for further details. Data : CHK --- The converted housekeeping data is simply composed of the digital number to physical unit converted housekeeping data plus associated timing and spatial data. The data is recorded in a time-series, and is grouped by day. RSCI ---- The rectified science data is simply the LEND science data with additional timing and spatial data added in. The RSCI is similar to the EDR SCI data except that it includes all spacecraft positional information and UTC time conversions. Data is recorded as a time-series DLD --- Derived LEND data are composed of corrected detector counts, background counts, and the associated timing and spatial information. The eleven background count fields are derived from count data collected during the cruise phase of the mission. The eleven detector count fields are the corrected counts at the detector of interest over one collection interval. Timing and spatial data provided with the counts include spacecraft clock values and spacecraft geometry data. The times and spatial fields are all recorded at the center of the collection interval. DLX --- Extended derived LEND data provide supplemental data for DLD data, including detector count uncertainties, a calculated sum of corrected counts in the 4 CSETN detectors, and the associated timing information. The times are all recorded at the center of the collection interval. ALD ---- Averaged LEND Data products are composed of averaged normalized counting rates and the associated timing, spatial and engineering information. The ALDs consists of the cumulative background subtracted and normalized counts of neutrons at the nine LEND detectors averaged over the 0.5 latitude longitude and a synodic period. Please refer to the RDR SIS located in the documents directory that accompanies this release for a full description of how LEND spectra are processed to yield averaged normalized counting rates and orbital neutron fluxes. The timing and spatial data provided with each ALD record include the time and spatial range over which the average was generated. ALF ---- Averaged LEND Fluxa products are composed of orbital neutron fluxes and the associated timing, spatial and engineering information. The ALFs consists of the cumulative background subtracted and normalized counts of neutrons at the nine LEND detectors averaged over the 0.5 latitude longitude and a synodic period. Please refer to the RDR SIS located in the documents directory that accompanies this release for a full description of how LEND spectra are processed to yield averaged normalized counting rates and orbital neutron fluxes. The timing and spatial data provided with each ALD record include the time and spatial range over which the average was generated. Ancillary Data : Ancillary data needed to understand the LEND data processing can be found in the RDR SIS document located in the document folder that accompanies this release. Coordinate System : Lunar Reconnaissance Orbiter (LRO) reduced data record (RDR) data use lunar planetocentric/body-fixed coordinates with east-positive longitude from 0 to 360 degrees. A mean Earth/polar axis (ME) reference system (also called the mean Earth/rotation system) is used, with the z axis being the mean rotational pole and with the prime meridian (zero degrees longitude) defined by the mean Earth direction. The ME reference system is used for all LRO archival data. This LRO standard is documented in 'A Standardized Lunar Coordinate System for the Lunar Reconnaissance Orbiter, LRO Project White Paper, 451-SCI-000958, Version 3, January 30, 2008'. Using coordinates in the ME system is consistent with recommendations from the International Astronomical Union (IAU)/International Association of Geodesy (IAG) Working Group on Cartographic Coordinates and Rotational Elements. A Jet Propulsion Laboratory (JPL) planetary and lunar ephemeris and corresponding Euler angle set are used to define an ME frame to which the LRO data are registered. The LRO Data Working Group (LDWG) determines which ephemeris and Euler angle set should be used. Alternatively, LRO data can be registered to an existing or new reference frame in the ME system, via ties to surface points known in the frame (examples include Lunar Laser Ranging (LLR) retroreflectors, points in images and Digital Elevation Models). When a JPL planetary and lunar ephemeris is used, the JPL Navigation and Ancillary Information Facility (NAIF) provides the necessary lunar ephemeris file (SPK) and binary lunar orientation file (PCK) in a Principal Axes (PA) reference frame for use with the SPICE Toolkit. NAIF also provides the frames kernel (FK) used for accessing the PA orientation in the PCK and for transforming from the PA frame to the ME frame. Alternatively, the JPL lunar ephemeris information is available in an ASCII format not requiring the use of the SPICE Toolkit. This information is available from a JPL website: http://ssd.jpl.nasa.gov. Software : No LEND specific software is provided with this data set. PDS-labeled images and tables can be viewed with the program NASAView, developed by the PDS and available for a variety of computer platforms from the PDS web site http://pds.nasa.gov/tools/software_download.cfm. There is no charge for NASAView. Media/Format : The LEND RDR will be delivered using DVD media. Formats will be based on standards for such products established by the Planetary Data System (PDS) [PDSSR2006].
DATA_SET_RELEASE_DATE 2010-03-15T00:00:00.000Z
START_TIME 2010-03-15T12:00:00.000Z
STOP_TIME N/A (ongoing)
MISSION_NAME LUNAR RECONNAISSANCE ORBITER
MISSION_START_DATE 2009-06-18T12:00:00.000Z
MISSION_STOP_DATE N/A (ongoing)
TARGET_NAME MOON
TARGET_TYPE SATELLITE
INSTRUMENT_HOST_ID LRO
INSTRUMENT_NAME LUNAR EXPLORATION NEUTRON DETECTOR
INSTRUMENT_ID LEND
INSTRUMENT_TYPE CALORIMETER/SPECTROMETER
NODE_NAME Geosciences
ARCHIVE_STATUS LOCALLY_ARCHIVED
CONFIDENCE_LEVEL_NOTE Confidence Level Overview : The data presented in the LEND RDR is processed for engineering units and combined with converted timing. Accuracy of the data presented here is dependent on appropriate use of SPICE and pre-flight calibration data for engineering unit conversions. Review : The LEND RDR was reviewed internally by the LEND team prior to release to the PDS. PDS also performed an external peer review of the LEND RDR. Data Coverage and Quality : Data reported are derived from the minimally processed data received from the orbiter during nominal LEND operations. All data received is reformatted into one of the EDR data types. RDR data is produced from the EDR data set, which by definition is of good quality. Limitations : The RDR data set is limited by any errors in the EDR data set. Data Compression : No data compression is used.
CITATION_DESCRIPTION Boynton, W.V., 2009 Lunar Reconnaissance Orbiter Lunar Exploration Neutron Detector RDR Data V1.0,LRO-L-LEND-4/5-RDR-V1.0, NASA Planetary Data System, 2009.
ABSTRACT_TEXT Calibrated or converted housekeeping and scientific data collected from the Lunar Exploration Neutron Detector aboard the Lunar Reconnaissance Orbiter.
PRODUCER_FULL_NAME WILLIAM BOYNTON
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