Overview : The Dawn Mission's Gamma Ray and Neutron Detector (GRaND) is a nuclearspectrometer that will collect data needed to map the elementalcomposition of the surfaces of 4-Vesta and 1-Ceres [PRETTYMANETAL2003B,PRETTYMANETAL2011, PRETTYMANETAL2012]. GRaND measures the spectrum ofplanetary gamma rays and neutrons, which originate from cosmic rayinteractions and radioactive decay within the surface, while the spacecraft(S/C) is in orbit around each body. The instrument, which is mounted on the+Z deck of the S/C, consists of 21 sensors designed to separately measureradiation originating from the surface of each asteroid and backgroundsources, including the space energetic particle environment and cosmicray interactions with the spacecraft. The nuclear spectroscopy dataprovided by GRaND will be analyzed to determine the abundance of majorrock forming elements, such as O, Fe, Ti, Si, Al, Mg, Ca, Cl andradioactive elements, including K and Th, as well as light-elements suchas H, C, and N, which are constituents of ices and the products ofaqueous alteration of silicate minerals and ices. The GRaND Experimental Data Records (EDR) are a time-ordered collectionof gamma ray and neutron counting data and histograms acquired by GRaNDduring different phases of the Dawn Mission, including assembly-test-and-launch- operations (ATLO), cruise, Mars Gravity Assist (MGA), andscience mapping at 4-Vesta and 1-Ceres. The dataset also includesstate-of-health data (instrument settings, temperature and voltagereadings) needed for scientific analysis of the neutron and gamma raydata. The EDR is an intermediate data product (Level 1A) that is derivedfrom Raw Data Records (Level 0) using reversible operations. The Level1A are the lowest level of GRaND data archived in the PDS, from whichall higher order data sets are derived. To support timely delivery ofhigher order products, the Level 1A data are processed using anautomated pipleline, which operates on Level 0 data when it is queriedby the DSC. The data set consists primarily of ASCII tables, divided into threefunctional categories: auxilliary information (AUX); gamma ray spectraand event data (GAMMA); and neutron spectra and event data (NEUTRON).Gamma ray and neutron event data are recorded in binary files. Some ofthe data in the ASCII files, which are human-readable, are repeated inthe binary files to aid in the verification of user-written routines. The telemetry for GRaND consists of science and state-of-health data,accumulated over consecutive time intervals to produce a time-series dataset. Each science data record includes scalers, histograms, and event dataaccumulated over an interval specified by the commandable parameterTELREADOUT, with units of seconds. The state of health data include averagetemperatures, voltages, and instrument state data acquired during timeintervals specified by the commandable parameter TELSOH (also in seconds).Both intervals are adjusted, depending on the measurement conditions andobjectives for each mission phase. During mapping, TELREADOUT will be set tosub-sample spatial pixels defined on the surface of Vesta or Ceres. Duringcruise, TELREADOUT was generally set to large values (e.g., 210s) to minimizedata volume. TELSOH is generally set to subsample the science accumulationinterval, providing information needed to determine, for example, whether andhow many times the science scalers have rolled over. GRaND has 23 scalers, which are described in the Paramters section.Scalers are simply pulse counters. They accumulate counts over time. Thevalue of the scaler registers are read out at the end of each scienceaccumuluation interval and then reset to zero to begin the next interval.The same registers are read out at each state-of-health time step. Becausethe state-of-health data are acquired at a higher cadence than the sciencedata, the accumulation of counts can be monitored during each TELREADOUTinterval. The 16-bit scalers roll over (return to zero) when they exceed65535 counts. Rollover can be detected and counted as a sawtooth pattern inthe state-of-health telemetry if TELSOH is set to be smaller than TELREADOUT.For example, if a single reset is observed for a scaler in the state-of-healthtelemetry, then the counts observed in the science telemetry need to beincreased by 65536. Properly accounting for rollover is particularly importantfor determining dead time from the scaler counting data. The data are downloaded regularly from the spacecraft by the Ground DataSystem. The UCLA Dawn Science Center (DSC) captures all of the payloadinstrument telemetry frames as binary files after the data have beencleaned up in post-pass processing to produce reconstructed Level-0data. The files are inventoried within the Dawn Science Database (DSDb)and are retrieved by the GRaND team, which unscrambles, decompresses,decodes, and formats the raw telemetry data into scientifically usefuldata files. The decompressed and decoded data, along with theirrequired PDS documentation, form the Level-1A EDR data sets. The Level-1a EDR data are determined by performing reversible operations on theLevel-1a data set, to produce counting data and spectral products usefulfor mapping.  Parameters : The EDR data are derived from Level 0 raw data queried by the DSC overirregular time periods, roughly aligned with the mission phaseboundaries. The DSC divides the Level 0 data into separate filescontaining state of health and science data packets. The Level 1apipeline operates on these files to produce the Level 1a archive. Thedirectory structure for the Level 1a data is given by  GRD-L1A-Y1M1D1-Y2M2D2_YCMCDC (top level directory) LEVEL1A_AUX (directory containing auxiliary data) LEVEL1A_GAMMA (directory containing gamma ray counting data) LEVEL1A_NEUTRON (directory containing neutron counting data) The top level directory name contains the SCET UTC dates for the firstand last science data records (Y1M1D1 and Y2M2D2, respectively), and thecreation date (YCMCDC) for the archive. For example, forGRD-L1A-090217-090218_090517, the first science data record was acquiredon 17- Feb-2009. The last science data record was acquired on 18-Feb-2009. The archive was created by the pipeline on 17-May-2009. The LEVEL1A_AUX directory contains the following files derived from theLevel 0 state-of-health and science data:  GRD-L1A-Y1M1D1-Y2M2D2_YCMCDC-STA.TAB - Instrument state file. The instrument state file contains the instrument settings, including the mode, power supply states, high voltage settings, the data accumulation interval, and coincidence windows. The first record of the state-of-health file is recorded in the state file, stamped with SCET UTC. Thereafter, rows are added only when the instrument settings change.  GRD-L1A-Y1M1D1-Y2M2D2_YCMCDC-RDG.TAB - Instrument readings file. This file contains a time-ordered list of temperature and voltage readings averaged over each state-of-health accumulation interval (TELSOH), converted to physical units.  GRD-L1A-Y1M1D1-Y2M2D2_YCMCDC-SOH-SCL.TAB - State of health scaler data. This file contains a time-ordered list of the scaler data recorded in the state-of-health telemetry. The accumulation time for the scaler data is TELSOH. Note that the scalers are set to zero the start of each science accumulation interval (TELREADOUT). If the state-of-health accumulation interval is selected to subsample the science interval, then the state-of-health scalers can be used to detect and correct for rollover of the science scalers, such as the dead time counter.  GRD-L1A-Y1M1D1-Y2M2D2_YCMCDC-SCI-SCL.TAB - Science scaler data. This file contains a time-ordered list of the scaler data recorded in the science telemetry. The accumulation interval for the scalers is TELREADOUT.  For each science and state of health record, values for 23 scalers are recorded in the -SCI-SCL.TAB and -SOH-SCL.TAB files, respectively.  The scalers provide the following information:  Index Description ------------ ----------- 0 Dead time counts 1 BGO overload events 2 CZT overload events 3 +Z phoswich overload events 4 -Y BLP overload events 5 +Y BLP overload events 6 -Z phoswich overload events 7 +Z phoswich CAT4 events 8 -Y BLP CAT4 events 9 +Y BLP CAT4 events 10 -Z phoswich CAT4 events 11 Early second interaction events 12 Multiple-crystal CZT events 13 Valid CZT events (CAT10) 14 Coincidence BGO and CZT events (CAT7) 15 Coincidence of three or more sensor elements 16 Total events processed by GRaND 17 Number of single CZT events (CAT10) in the gamma ray event buffer 18 Number of BGO-CZT coincidence events (CAT7) in the gamma ray event buffer 19 Number of events (CAT4) in the neutron event buffer 20 Total number of events allowed in the gamma ray event buffer 21 Number of single CZT events (CAT10) allowed in the gamma ray event buffer 22 Number of events allowed in the neutron event buffer  Note that indices 0 through 19 are for 16-bit counters, which are reset at the end of every science accumulation interval specified by TELREADOUT. If the state-of-health accumulation interval is adjusted to subsample the science accumulation interval (for example, TELREADOUT : n * TELSOH, where n is a whole number), then the scalers will monotonically increase during each acquisition interval, unless overflow occurs. A rollover counter is not provided; however, for situations in which the counting rate is high or the accumulation intervals are large, the number of rollovers for individual scalers can be determined from the SOH scaler data if TELSOH is set to subsample the science accumulation interval. In situations where the counting rate is changing, abrupt changes in the scaler values can also indicate that rollover has occurred. Rollover is treated in production of the Level1b RDR data.  Indices 20 through 21 are maximum values for the number of events that can be recorded in the event buffers. The number of gamma ray and neutron events is commandable and can be adjusted. The total number of gamma ray and neutron events must be less than 6677. The LEVEL1A_GAMMA directory contains the following science data files:  GRD-L1A-Y1M1D1-Y2M2D2_YCMCDC-BGO.TAB This file contains a time-ordered list of pulse height spectra (1024 channels with units of uncorrected counts/channel) acquired by the BGO sensor.  GRD-L1A-Y1M1D1-Y2M2D2_YCMCDC-EMG.DAT This file contains gamma ray event data as a time series in a binary file. Each row of this file contains data from a science data record. Each science data record contains a list of 3876 events. Each event [e.g. i:0,...3875] is specified by ID_CZT[i], the index of the CZT sensor struck, CH_CZT[i], the pulse height (0-1023) recorded for ID_CZT[i], and CH_BGO[i], the pulse height (0-511) recorded for the BGO scintillator (see GRD_L1A-GAMMA_EVENTS.FMT). If CH_BGO[i]:0, then the event was CAT7 (coincidence between the BGO and a single CZT sensor). Otherwise, the event was CAT10 (interaction with a single CZT sensor). See the instrument catalog and PRETTYMANETAL2011 for a detailed description of the event data and examples. In addition, each row of the -EMG.DAT file includes the SCLK, and 23 scalers (SCALER_SCI). These can be compared to values found in the ASCII format -SCI-SCL.TAB (e.g. for debugging programs that read the binary data). The binary file can also be examined using NASAview and IDL routines accomanying this archive in EXTRAS. The LEVEL1A_NEUTRON directory contains the following science data files:  GRD-L1A-Y1M1D1-Y2M2D2_YCMCDC-PHOS_MZ.TAB GRD-L1A-Y1M1D1-Y2M2D2_YCMCDC-PHOS_PZ.TAB These files contain time ordered lists of the 256-channel CAT1 pulse height spectra for the +Z and -Z phoswiches. Note that the naming convention for the top, bottom, and side scintillators is determined by the instrument coordinate system.  GRD-L1A-Y1M1D1-Y2M2D2_YCMCDC-BGO2_MZ.TAB GRD-L1A-Y1M1D1-Y2M2D2_YCMCDC-BGO2_PZ.TAB GRD-L1A-Y1M1D1-Y2M2D2_YCMCDC-BGO2_MY.TAB GRD-L1A-Y1M1D1-Y2M2D2_YCMCDC-BGO2_PY.TAB These files contain time ordered lists of the 64-channel CAT2 BGO pulse height spectra for coincidences with the BGO and the four BLP sensors.  GRD-L1A-Y1M1D1-Y2M2D2_YCMCDC-BLP2_MZ.TAB GRD-L1A-Y1M1D1-Y2M2D2_YCMCDC-BLP2_PZ.TAB GRD-L1A-Y1M1D1-Y2M2D2_YCMCDC-BLP2_MY.TAB GRD-L1A-Y1M1D1-Y2M2D2_YCMCDC-BKP2_PY.TAB These files contain time ordered lists of the 64-channel CAT2 BLP pulse height spectra for coincidences with the BGO and the four BLP sensors.  GRD-L1A-Y1M1D1-Y2M2D2_YCMCDC-EMN.DAT This file contains the fast neutron double pulse event data (CAT4) as a binary time series. Each row of this file contains data from a science data record. Each science data record contains a list of 2880 events. Each event [e.g. i:0,...,2879] is specified by ID_FIRST[i], the index of the BLP scintillator that produced the first pulse (0:+Z phoswich; 1:-Y BLP; 2:+Y BLP; 3:-Z phoswich), CH_FIRST[i], the amplitude of the first pulse (0-63), ID_SECOND[i], the index of the BLP scintillator that produced second pulse (0-3), CH_SECOND[i], the amplitude of the second pulse (0-63), and the time to second pulse (0-255), with units of 100 ns per data number. See the instrument catalog and PRETTYMANETAL2011 for a detailed description of the event data and examples. In addition, each row of the -EMN.DAT file includes the SCLK, and 23 scalers (SCALER_SCI). These can be compared to values found in the ASCII format -SCI-SCL.TAB (e.g. for debugging programs that read the binary data). The binary file can also be examined using NASAview and IDL routines accomanying this archive in EXTRAS.  Processing : The Level 1A data are automatically processed using a pipeline, whichoperates on files queried by the DSC over selected time intervals. EachDSC query separates the GRaND data into files containing state-of-healthand science data records, in the order in which they were received onthe ground and with corrupted packets removed. The state-of-health dataare further divided into real time telemetry data and playback data.The science data are stored in a single raw data file. The pipeline merges the state-of-health data from the playback andrealtime files to produce a time-ordered-list of records. Selected dataare extracted to produce the Level 1A AUX files. Internal temperaturereadings are converted from data numbers (DN) to engineering units usinga linear function determined during ground calibration: T (degrees C) :0.4354 DN - 0.4354. The high voltage readings for the high voltage powersupplies are reported in engineering units using the conversion V(Volts) : 1500 DN/255. The CZT differential bias voltage is convertedusing V (Volts) : 0.405 DN. The science data are decompressed, decoded, separated by functionalityand written as time-ordered ASCII tables and binary time series. Theraw histograms (CAT1, CAT2, and CAT9) are represented as 8 bit numberswhich are decompressed and reported as 16 bit, unsigned integers. The gamma ray event buffer can store up to 3876 events for each scienceaccumulation interval. Each event is packed into 3 bytes, which containthe ID of the CZT sensor, the CZT pulse amplitude, and the BGO pulseamplitude. The vales for each event are extracted and stored as abinary time series. When the gamma ray event buffer is not full, nullevents are reported as zeros, such that each row of the Level 1A timeseries contains 3876 events. The neutron event buffer can store up to 2800 events for each sciencedata accumulation interval. Each event is packed into 3 bytes, whichcontain the BLP sensor ID and pulse amplitude for the first interaction,the BLP sensor ID and pulse amplitude for the second interaction, andthe time between pulses. The time between pulses has units of 100nanoseconds/DN. The vales for each event are extracted and stored as abinary time series. The pulse amplitudes are uncalibrated for Level 1A.When the gamma ray event buffer is not full, null events are reported aszeros, such that each row of the Level 1A time series contains 2800events.  Ancillary Data : The Level 1A data include ancilliary data in the form of SCET UTCstrings reported in each row of the Level 1A data tables and timeseries. The UTC strings are determined from the spacecraft clock ticksrecorded in each state-of-health packet and for the first packet in eachscience data record using NAIF SPICE (leap seconds kernel). Thisinformation is used in Level 1B processing to accurately determine themid-point of each science accumulation interval, which is needed formapping.  Coordinate System : The instrument coordinate system (Fig. 1) determines the namingconvention of the sensors and orientation of the instrument relative tothe spacecraft. The use of MZ indicates a sensor on the -Z (zenith-facing during mapping) side of GRaND; PZ indicates the sensor is on the+Z (spacecraft) side; MY indicates the sensor is on the -Y side(inboard) side of the instrument; and PY indicates the sensor is on the+Y side (outboard, towards the +Y solar panel) side of the instrument.The phototube assembly, marked 'P' on the diagram in Fig. 1 points alongthe +X axis (towards the high gain antenna).  ................. . ooooooooooooo . . o o . . o o . . o +Z o . . o (PZ) o . . o o .---> +Y (PY) . ooo ooo . . P P . . P P . . PPPPPPPPP . . . ................. | v +X (PX) Figure 1. The coordinate system for GRaND is the same as that of theS/C. For the diagram above, the observer is looking in the -Z (MZ)direction and can see the outline of the phoswich assembly (o) on the +Zside of GRaND. The phototubes are on the +X side and the scintillatorsare on the -X side. During mapping at Vesta and Ceres, the planetarysurface is in the +Z direction.  Software : Proprietary software is not needed in order to use the EDR data;however, Interactive Data Language (IDL) functions are provided in the Extrasdirectory to read selected EDR data into a structures for analysis andvisualization. The IDL functions are compatible with IDL Version 7.0 orhigher, distributed by Exelis Visual Information Solutions. A documentillustrating the use of these functions is provided.  Media/Format : The EDR label and data files are delivered by electronic transmission tothe PDS. The neutron and gamma ray binary event data were written inbig endian IEEE binary format (MSB order).

Review : The EDR will be reviewed internally by the Dawn Science Team prior tosubmission to the PDS. The PDS will also conduct an external peerreview of the EDR prior to releasing the data to the general public.  Data Coverage/Quality : The Level 1A EDR includes all of the available data acquired during flight.The archive contains gaps in time when the instrument is off during cruise orin STANDBY or ANNEAL mode for which science data are not acquired. During ATLO, ICO, and EMC, state-of-health data were decimated by afactor of 3 for storage in the virtual recorder on board the spacecraft.Consequently, playback data contained every third state-of-healthpacket. Full sampling of GRaND housekeeping data was availableinfrequently during the acquisition of real-time telemetry. Thespacecraft flight software was modified to remove the decimation priorto GRaND power on for Mars Gravity Assist (at UTC/ SCET 2009-020/21:19:11), and, thereafter, housekeeping data volume was controlledby the selection of TELSOH. Consequently, fully-sampled housekeepingdata are available in the EDR following 20-Jan-2009. GRaND's scalers do not have accompanying roll-over counters. Duringsolar particle events or long accumulation times, it is possible thatone or more of the scalers can exceed the maximum number of counts(65535), restarting at 0. In fact, the some scalers, such as the deadtime counter, can roll over multiple times. The number of of times ascaler has rolled over can be determined by watching for abrupt changesin the science scaler data and by analyzing the state-of-health scalerdata when the state-of-health readout interval (TELSOH) is set tosubsample the science accumulation interval (TELREADOUT) (for example,see Prettyman et al., 2011). Corrections for rollover, for example todetermine dead time, are made in the RDR (Level 1b) datasets. Successive EDR directories contain short overlapping time periods, such thata few science data records are repeated. Care should be taken to eliminaterepeated records when processing EDR from multiple directories. Gaps in theEDR data set can occur due to missing packets (e.g. occultations) and forperiods of time when the instrument was off following spacecraft safingevents. During Vesta encounter, the Dawn spacecraft entered safe modesix times: on 27-Jun-2011 (VSA), 21-Sep-2011 (VSH), 4-Dec-2011 (VTL),14-Jan-2012 (VSL), 21-Feb-2012 (VSL), and 8-Aug-2012 (VTC). GRaND was notpowered back on following the last safe mode entry. Recovery of GRaND wasdelayed due to anomalous conditions for the 21-Sep-2011 and 14-Jan-2012events. Recovery for the latter event required resetting the communicationslink between GRaND and the spacecraft; however, GRaND was found in ananomalous state following recovery from the 21-Sep-2011 event, which isdescribed here. GRaND was powered on and configured for science data acquisition on22-Sep-2011. It was discovered that following entry into NORMAL mode andprior to application of high voltage, the BGO counting rate was about80 hertz, with a sharp peak around channel 100. During normal operations, nocounts would have been observed at this stage. At nominal high voltagesettings, the BGO pulse height spectrum was found to be noisy and thespectrum was shifted and distorted (see EDRs in the 110922-110928 directory).The behavior was stable and the instrument was allowed to operate at nominalhigh voltages for about a week while the anomaly was investigated.On 28-Sep-2011, GRaND was commanded into STANDBY mode, with all HV suppliesoff and the low voltage supplies enabled. The anomaly review panel concluded that it would do no harm to GRaND to cyclepower; however, the panel also suggested that GRaND remained powered off fora few days in the event that the anomaly was caused by a damaged component,which might recover with power removed. The instrument was powered off on30-Sep-2011 and powered on and configured on 4-Oct-2012. The instrument wasfound to be nominal upon entry into NORMAL mode with the +/-5V supply andhigh voltage supply enabled. Given the absence of the 80-Hz noise, thedecision was made to ramp up the high voltages for the BGO scintillator. Thiswas carried out on 5-Oct-2012, and the spectrum was found to be nominal. Thehigh voltages for the remaining scintillators were ramped up the same day;however, the high voltages for the CZT were not ramped up until 11-Oct-2011.The system was fully configured and restored to nominal operations on12-Oct-2011. Although the root cause has not been identified, it was determined that theabrupt removal of power from GRaND upon entry into safe mode was not likelyhave caused catastrophic damage to analog components. The analog or digitalcircuitry appears to have an anomalous state that can be entered uponapplication of power. Thus, the problem was mitigated by monitoring the eventcounter on entry into NORMAL mode. If anomalous counts are observed, theinstrument can be power cycled. This operational measure was effectivelyimplemented during the recovery from the 21-Feb-2011 safing. The BGO anomaly and recovery affects EDRs in directories with the followingdate ranges: 110922-110928111004-111006111006-111011111011-111016 For completeness, data corrupted (e.g. due to transmission errors) are notexcluded from the dataset; however, instances of corrupt data are rare,restricted to the 120225-120303 directory (VSL), primarily on two days:29-Feb-2012 and 1-Mar-2012. User's should be cautious when processing datain this directory. Telemetry checksums are discarded in queries of instrumentdata by the DSC. Consequently, corrupt data can only be identified byanomalies in scaler and spectral data (e.g. incongruous patterns in counts ordiscontinuous pulse height spectra). Corrupt data are partially excludedfrom the EDR dataset by two mechanisms: 1) packet headers with incorrect SCLKvalues or other invalid information recognized by the query software arenaturally excluded; 2) incomplete science data records (e.g. detected by gaps)in the packet sequence counter) are discarded by the EDR processing code.These result in gaps in the EDR science data. Some unknown portion of therecords may be recognized as valid, yet still contain corrupted science data.These are not exluded from the archive. Some spectral data products contain artifacts, for example, abrupt increasesin counts for the highest channel or a nonphysical changes in countsat high channels (e.g. for the CAT1 -Z sensor). The former is likely fromevents that do not exceed the overload threshold, but are not on scale.These wind up in the last channel. In addition, some distortion can occurfor large pulses processed by the analog pulse processing circuit. This mayaccount for the roll-off observed for high channels for the -Z sensor (e.g.above channel 230).  Limitations : The EDR is a low-level data product, which requires significantprocessing prior to use in scientific analysis.