Data Set Information
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| DATA_SET_NAME |
DAWN GRAND RAW (EDR) CRUISE CHECKOUT/BACKGROUND COUNTS V1.0
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| DATA_SET_ID |
DAWN-X-GRAND-2-EDR-CRUISE-COUNTS-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 |
Acronyms and Abbreviations : BGO Bismuth Germanate EDR Experimental data records (Level 1A) EPG Spacecraft Ephemerides, Pointing, and measurement Geometry GCR Galactic Cosmic Ray HED Howardite, Eucrite, and Diogenite meteorites PDS Planetary Data System RDR Reduced data records (Level 1B) SBN Small Bodies Node of the Planetary Data System SCLK Spacecraft Clock Overview : The Dawn Mission's Gamma Ray and Neutron Detector (GRaND) is a nuclearspectrometer that will collect data needed to map the elemental compositionof the surfaces of 4-Vesta and 1-Ceres [PRETTYMANETAL2003B]. GRaND measuresthe spectrum of planetary gamma rays and neutrons, which originate fromcosmic ray interactions and radioactive decay within the surface, while thespacecraft (S/C) is in orbit around each body. The instrument, which ismounted on the +Z deck of the S/C, consists of 21 sensors designed toseparately measure radiation originating from the surface of each asteroidand background sources, including the space energetic particle environmentand cosmic ray interactions with the spacecraft. The nuclear spectroscopydata provided by GRaND will be analyzed to determine the abundance of majorrock forming elements, such as O, Fe, Ti, Si, Al, Mg, Ca, Cl and radioactiveelements, including K and Th, as well as light-elements such as H, C, andN, which are constituents of ices and the products of aqueous alterationof silicate minerals and ices. The GRaND Experimental Data Records (EDR) are a time-ordered collection ofgamma ray and neutron counting data and histograms acquired by GRaND duringdifferent phases of the Dawn Mission, including assembly-test-and-launch-operations (ATLO), cruise, Mars Gravity Assist (MGA), and science mappingat 4-Vesta and 1-Ceres. The dataset also includes state-of-health data(instrument settings, temperature and voltage readings) needed forscientific analysis of the neutron and gamma ray data. The EDR is anintermediate data product (Level 1A) that is derived from Raw Data Records(Level 0) using reversible operations. The Level 1A are the lowest levelof GRaND data archived in the PDS, from which all higher order data sets arederived. To support timely delivery of higher order products, the Level 1Adata are processed using an automated pipleline, which operates on Level 0data when it is queried by the DSC. The data set consists primarily of ASCII tables, divided into threefunctional categories: auxilliary information (AUX); gamma ray spectra andevent data (GAMMA); and neutron spectra and event data (NEUTRON). Gamma rayand neutron event data are recorded in binary files. Some of the data in theASCII files, which are human-readable, are repeated in the binary files toaid in the verification of user-written routines. The telemetry for GRaND consists of science and state-of-health data,accumulated over time intervals, which are commandable. Each science datarecord includes scalers, histograms, and event data accumulated over aninterval specified by the commandable parameter TELREADOUT (s). The state ofhealth data include average temperatures, voltages, and instrument state dataacquired during time intervals specified by the commandable parameterTELSOH (s). Both intervals are adjustable, depending on the measurementconditions and objectives for each mission phase. During mapping, TELREADOUTwill be set to sub-sample spatial pixels defined on the surface of Vesta orCeres. During cruise, TELREADOUT was generally set to large values (e.g.,210s) to minimize data volume. TELSOH is generally set to subsample thescience accumulation interval, providing information needed to determinewhether and how many times the science scalers have rolled over andinformation needed to precisely determine the start time of the scienceacquisition interval. 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 been cleanedup in post-pass processing to produce reconstructed Level-0 data. The filesare inventoried within the Dawn Science Database (DSDb) and are retrieved bythe GRaND team, which unscrambles, decompresses, decodes, and formats the rawtelemetry data into scientifically useful data files. The decompressed anddecoded data, along with their required PDS documentation, form the Level-1AEDR data sets. The Level-1a EDR data are determined by performing reversibleoperations on the Level-1a data set, to produce counting data and spectralproducts useful for mapping. Parameters : The EDR data are derived from Level 0 raw data queried by the DSC overirregular time periods, generally determined by the pattern of downlinksfrom the spacecraft. 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 first andlast science data records (Y1M1D1 and Y2M2D2, respectively), and the creationdate (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 reset at the end 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 varues 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 binary time series. 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 neutron event data as a binary time series. Processing : The Level 1A data are automatically processed using a pipeline, whichoperates on files queried by the DSC over selected time intervals. Each DSCquery separates the GRaND data into files containing state-of-health andscience data records, in the order in which they were received on the groundand with corrupted packets removed. The state-of-health data are furtherdivided into real time telemetry data and playback data. The science dataare stored in a single raw data file. The pipeline merges the state-of-health data from the playback and realtimefiles to produce a time-ordered-list of records. Selected data are extractedto produce the Level 1A AUX files. Internal temperature readings areconverted from data numbers (DN) to engineering units using a linear functiondetermined during ground calibration: T (degrees C) : 0.4354 DN - 0.4354.The high voltage readings for the high voltage power supplies are reportedin engineering units using the conversion V (Volts) : 1500 DN/255. TheCZT differential bias voltage is converted using 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 numbers whichare 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, whichcontain the ID of the CZT sensor, the CZT pulse amplitude, and the BGO pulseamplitude. The vales for each event are extracted and stored as a binarytime series. When the gamma ray event buffer is not full, null events arereported as zeros, such that each row of the Level 1A time series contains3876 events. The neutron event buffer can store up to 2800 events for each science dataaccumulation interval. Each event is packed into 3 bytes, which arecontain the BLP sensor ID and pulse amplitude for the firstinteraction, the BLP sensor ID and pulse amplitude for the secondinteraction, and the time between pulses. The time between pulses hasunits of 100 nanoseconds/DN. The vales for each event are extracted andstored as a binary time series. The pulse amplitudes are uncalibratedfor Level 1A. When the gamma ray event buffer is not full, null eventsare reported as zeros, such that each row of the Level 1A time seriescontains 2800 events. Ancillary Data : The Level 1A data include ancilliary data in the form of SCET UTC stringsreported in each row of the Level 1A data tables and time series. The UTCstrings are determined from the spacecraft clock ticks recorded in eachstate-of-health packet and for the first packet in each science data recordusing NAIF SPICE (leap seconds kernel). This information is used in Level 1Bprocessing to accurately determine the mid-point of each science accumulationinterval, which is needed for mapping. Coordinate System : The instrument coordinate system (Fig. 1) determines the naming convention ofthe sensors and orientation of the instrument relative to the 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; MYindicates the sensor is on the -Y side (inboard) side of the instrument; andPY indicates the sensor is on the +Y side (outboard, towards the +Y solarpanel) side of the instrument. The phototube assembly, marked 'P' on thediagram in Fig. 1 points along the +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 the S/C.For the diagram above, the observer is looking in the -Z (MZ) direction andcan see the outline of the phoswich assembly (o) on the +Z side of GRaND.The phototubes are on the +X side and the scintillators are on the -X side.During mapping at Vesta and Ceres, the planetary surface is in the +Zdirection. Software : Proprietary software is not needed in order to use the EDR data; however, anInteractive Data Language (IDL) functions (GRD_READ_L1A_SOH.PRO andGRD_READ_L1A_SCIENCE.PRO) are provided to read selected EDR data into astructure for analysis and visualization. The IDL functions are compatiblewith IDL Version 7.0, distributed by ITT Visual Information Solutions,Boulder, CO (2008). The documentation is included at the beginning of thefunctions. Media/Format : The EDR label and data files are delivered by electronic transmission to thePDS. The neutron and gamma ray binary event data were written in big endianIEEE binary format (MSB order).
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| DATA_SET_RELEASE_DATE |
3000-01-01T00:00:00.000Z
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| START_TIME |
2007-10-16T05:36:42.000Z
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| STOP_TIME |
2014-07-01T12:01:00.000Z
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| MISSION_NAME |
DAWN MISSION TO VESTA AND CERES
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| MISSION_START_DATE |
2007-09-27T12:00:00.000Z
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| MISSION_STOP_DATE |
2018-10-31T12:00:00.000Z
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| TARGET_NAME |
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| TARGET_TYPE |
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| INSTRUMENT_HOST_ID |
DAWN
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| INSTRUMENT_NAME |
GAMMA-RAY AND NEUTRON DETECTOR
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| INSTRUMENT_ID |
GRAND
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| INSTRUMENT_TYPE |
NEUTRON SPECTROMETER
GAMMA RAY SPECTROMETER
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| NODE_NAME |
Small Bodies
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| ARCHIVE_STATUS |
LOCALLY ARCHIVED
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| CONFIDENCE_LEVEL_NOTE |
Review : The EDR will be reviewed internally by the Dawn Science Team prior tosubmission to the PDS. The PDS will also conduct an external peer reviewof the EDR prior to releasing the data to the general public. Data Coverage/Quality : With the exception of corrupted packets, the Level 1A EDR includes all of theavailable data acquired during flight. The archive contains gaps in timewhen the instrument is off during cruise or in STANDBY or ANNEAL mode forwhich science data are not acquired. During ATLO, ICO, and EMC, state-of-health data were decimated by a factor of3 for storage in the virtual recorder on board the spacecraft. Consequently,playback data contained every third state-of-health packet. Full sampling ofGRaND housekeeping data was available infrequently during the acquisition ofreal-time telemetry. The spacecraft flight software was modified toremove the decimation prior to GRaND power on for Mars Gravity Assist (TBD),and, thereafter, housekeeping data volume was controlled by the selection ofTELSOH. Consequently, fully-sampled housekeeping data are available in theEDR following TBD. Limitations : The EDR is a low-level data product, which requires significant processingprior to use in scientific analysis.
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| CITATION_DESCRIPTION |
Prettyman, T.H., DAWN GRAND RAW (EDR) CRUISECHECKOUT/BACKGROUND COUNTS V1.0. DAWN-X-GRAND-2-EDR-CRUISE-COUNTS-V1.0.NASA Planetary Data System, 2010.
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| ABSTRACT_TEXT |
The GRaND EDR are a time-ordered collection of gamma rayand neutron counting data and histograms acquired by GRaND during all phasesof the Dawn mission. The dataset includes state-of-health data, suchas temperature and voltage readings, needed for the analysis of the countingdata. The EDR is an intermediate data product derived from the raw datarecords using reversible operations. All higher order data products arederived from the EDR. An automated pipeline is used to process the EDR fromthe raw data records.
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| PRODUCER_FULL_NAME |
THOMAS H. PRETTYMAN
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| SEARCH/ACCESS DATA |
SBN PSI WEBSITE
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