Data Set Information
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| DATA_SET_NAME |
MESSENGER E/V/H GRNS 4 NEUTRON SPECTROMETER DDR V1.0
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| DATA_SET_ID |
MESS-E/V/H-GRNS-4-NS-DDR-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 |
Instrument Overview : The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) Neutron Spectrometer (NS) sensor consists of three scintillators, each wrapped separately and coupled to separate photo-multiplier tubes. The three scintillators are sensitive to neutrons of different energies: thermal neutrons (0.025 - 1 eV), epithermal neutrons (1eV - 500 keV), and fast neutrons (500 keV - 7 MeV). The first and third scintillators are lithium (6Li)-glass scintillators (LG1 and LG2) which respond to a combination of thermal and epithermal neutrons. The middle scintillator is a borated plastic (BP) scintillator that responds only to epithermal and fast neutrons due to its electronics setup. The interaction of galactic cosmic rays (GCR) with the surface of Mercury produces neutrons, some of which escape the surface and produce a neutron signal that can be measured by the orbiting NS sensor. The measured neutron energy spectrum reflects the transport properties of the surface composition and is sensitive to depths down to about 1 m. Thermal neutrons are sensitive to a variety of elements, including Fe, Ti, Gd, Sm, Cl, and C. Epithermal neutrons are mostly sensitive to H abundance. Fast neutrons can provide a good measure of average atomic mass. For the MESSENGER mission, the NS sensor will establish and map the abundance of H over most of the northern hemisphere of Mercury, providing significant new information regarding the potential presence of water ice within and near permanently shaded craters near the north pole. See the NS_INST.CAT file for more information and [GOLDSTENETAL2007] for full details. Data Set Overview : This data set consists of MESSENGER NS 'derived' data records (DDRs). There is 1 NS DDR standard data product (Neutron Count Rate, NS_DDR_NCR) and 1 NS DDR special data product (Neutron Composition, NS_DDR_NCP). The NCR data products are derived data consisting of net (background subtracted) neutron count rates from each of the three NS sensors, namely the two lithium glass (LG) sensors and the epithermal neutron singles data from the borated plastic (BP) sensor. A single DDR NCR data file contains the observations with a time tag corresponding to a given Earth day. Uncertainty values for each of these net count rates are also provided along with spacecraft ephemeris/geometry information. This ephemeris/geometry data are the same as given in the NS CDR files. The NS_DDR_NCP file contains fast and epithermal count rates as a function of latitude, along with simulated count rates for the cases of no hydrogen and for a thick layer of 100 wt. percent water ice in all radar bright regions. Processing Overview : The following operations are applied to the Calibrated Data Records (DDRs) to arrive at the Derived Data Records (DDRs): 1) Selection of valid data to eliminate times where the backgrounds from solar particle events are too high to enable net count rates to be derived. 2) Corrections to the NS spectra for gain varations. 3) Background subtraction from the NS spectra to arrive at the net neutron count rates. These corrections are not reversible such that the DDR is not directly derivable from the CDR dataset. Details of the processing are given in the document messns_processing.pdf located in the CALIB directory. Coordinate Systems : For planetary orbital and flyby data, the NS-specific data also have two coordinate systems (in addition to standard J2000 and Planetocentric body fixed) for expressing spacecraft velocity and attitude data: the nadir fixed coordinate system and the spacecraft fixed coordinate system. The nadir fixed coordinate system is defined as follows: * The z-axis is defined as the vector from the spacecraft center to the flyby or orbiting planet center. * The nadir fixed y-axis is defined as the cross product of the nadir z-axis and the spacecraft velocity vector (where both are expressed in the J2000 coordinate system). * The nadir fixed x-axis is defined as the cross product of the nadir fixed y-axis with the nadir fixed z-axis. The spacecraft fixed coordinate system is defined as follows: * The spacecraft fixed x-axis is the vector normal to the NS LG1 sensor and is parallel to the spacecraft solar panel booms. * The spacecraft fixed y-axis is in the direction from the spacecraft down the magnetometer boom. * The spacecraft fixed z-axis is the viewing direction from the instrument deck. Data : There is 1 NS DDR standard data product (Neutron Count Rate, NS_DDR_NCR) and 1 NS DDR special data product (Neutron Composition, NS_DDR_NCP). The NS_DDR_NCR files contain net neutron count rate data as derived from the LG and BP singles spectra. The net count rates are given in units of counts per second for each accumulation time interval. Derived uncertainty values for each count rate are also provided for each time step. Each NS_DDR_NCR file is organized as an ASCII text file and contains data collected over one Earth day. In addition to the count rates, spacecraft time and geometry information associated with each measurement are provided. These time and geometry values are the same as is given in the CDR files for each corresponding measurement. Three main processing steps are carried out for the derivation of the net neutron count rate data. First, data selections are made to exclude data taken during times of solar particle events when the charged particle flux is sufficiently high to affect the background in the NS sensors. The times of these exclusions are given below. Second, gain corrections are made to the NS spectra prior to deriving any net neutron counts. Finally, background subtraction algorithms are applied to the NS spectra through which the next neutron counts are derived. Details of the processing are given in the document messns_processing.pdf located in the CALIB directory. Please note that DDRs were generated for data collected during the 'Mercury Orbit' phase only. The general form of the NS_DDR_NCR file names is 'NS_DDR_ZZZYYYYDDDWWW.XXX,' where NS instrument identifier: represents the NS instrument. DDR data product identifier: DDR ZZZ data product name NCR - Neutron Count Rates YYYY four digit year corresponding to the start-time of the first record in the NS data file. DDD three digit day of the year corresponding to the start time of the first record in the NS CDR data file. WWW reserved character string to use during the course of the mission as necessary to identify 'special' data products. Nominal data products will be identified by ZZZ. .XXX the file extension (.DAT for binary files, .TAB for ascii files). The NCP data product contains latitude-binned relative neutron count rates taken during the primary MESSENGER mission from 26 March 2011 to 25 February 2012. Specifically, these data are the exact data points given in Figure 2 and Figure 3A from Lawrence et al., Science, 339, 292-296, 2013. The delivered values include measured and simulated data for fast and epithermal neutron data. The simulated data include two cases: one case assumes there is no hydrogen in Mercury's north polar radar bright regions; the other case assumes that the north polar radar bright regions contain 100 wt. percent H2O. The general form of the NS_DDR_NCP file names is 'NS_DDR_ZZZ.XXX,' where NS instrument identifier: represents the NS instrument. DDR data product identifier: DDR ZZZ data product name NCP - Neutron Composition Product .XXX the file extension (.TAB). See NS_CDR_DDR_SIS.PDF in the DOCUMENT folder of this volume for more information.
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| DATA_SET_RELEASE_DATE |
2015-03-06T00:00:00.000Z
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| START_TIME |
2011-03-25T12:00:00.000Z
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| STOP_TIME |
N/A (ongoing)
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| MISSION_NAME |
MESSENGER
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| MISSION_START_DATE |
2004-08-03T12:00:00.000Z
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| MISSION_STOP_DATE |
2015-04-30T12:00:00.000Z
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| TARGET_NAME |
MERCURY
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| TARGET_TYPE |
PLANET
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| INSTRUMENT_HOST_ID |
MESS
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| INSTRUMENT_NAME |
NEUTRON SPECTROMETER
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| INSTRUMENT_ID |
NS
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| INSTRUMENT_TYPE |
NEUTRON SPECTROMETER
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| NODE_NAME |
Geosciences
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| ARCHIVE_STATUS |
ARCHIVED_ACCUMULATING
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| CONFIDENCE_LEVEL_NOTE |
Confidence Level Overview : The NS DDR data have been processed as described in the 'MESSENGER Neutron Spectrometer (NS) EDR-to-CDR-to-DDR Processing' document (MESSNS_PROCESSING.PDF, CALIB directory). Data presented here are an accurate representation of the NS data as processed from the CDR files, where the processing includes data selection, gain correction, and background subtraction. Review : The NS DDR was reviewed internally by the NS team prior to release to the PDS. PDS also performed an external review of the NS DDR. Data Coverage and Quality : Data reported are the 'derived' data received from the spacecraft during the the following mission phases: 'Mercury Orbit', 'Mercury Orbit Year 2', and 'Mercury Orbit Year 3'. These mission phases are defined as: Start time End time Phase Name Date (DOY) Date (DOY) ----------------- ----------------- ----------------- Mercury Orbit 4 Mar 2011 (063) 17 Mar 2012 (077) Mercury Orbit Year 2 18 Mar 2012 (078) 17 Mar 2013 (076) Mercury Orbit Year 3 18 Mar 2013 (077) 17 Mar 2014 (076) PDS delivery 9 included NS DDR data acquired from March 25, 2011 to March 25, 2012. During this data delivery phase, the NS was shut off for nine consecutive days when the MESSENGER spacecraft passed through its first long eclipse period. The specific off period was from May 24, 2011 21:34:49 to June 3, 2011 0:17:49. Also during this data delivery phase, the high voltage (HV) to the LG and BP sensors was shut down six times during spacecraft thrusting maneuvers. Each time, the HV was shut down for approximately four hours while the spacecraft was near apoapsis. The specific times for the HV shut down are: June 15, 2011 16:12:08 - June 15, 2011 20:30:16; July 26, 2011 17:40:16 - July 26, 2011 21:55:16; September 7, 2011 11:38:16 - September 7, 2011 16:05:50; October 24, 2011 18:29:00 - October 24, 2011 23:16:00; December 5, 2011 12:36:00 - December 5, 2011 17:18:00; March 2, 2012 22:09:22 - March 3, 2012 02:47:54. The HV to the LG and BP sensors was shut down during a large solar particle event when the NS sensors were safed because of the large charged particle flux. The times for this HV shut down period were: March 7, 2012 0:24:42 - March 12, 2012 15:50:42. PDS delivery 11 included NS DDR data acquired from March 26, 2012 through March 17, 2013. The NS HV for the BP sensor was shut down twice from September 2012 to March 2013: first from September 20, 2012 at 09:40 UTC to September 24, 2012 at 17:38 UTC when the NS BP sensor went into safe mode due to an energetic particle event; second on March 16, 2013 from 06:53 UTC to 08:00 UTC when the NS BP sensor went into safe mode due to an energetic particle event. PDS delivery 13 includes NS DDR data acquired from March 18, 2013 to March 17, 2014. From March 18, 2013 to September 17, 2013 the NS HV was shut down six times into safe mode due to high rates from energetic particles: 1) April 24, 2013 to April 25, 2013; 2) May 2, 2013, 8:45 UTC to May 2, 2013, 9:16 UTC; 3) May 21, 2013, 8:57 UTC to May 21, 2013, 9:32 UTC; 4) May 21, 2013, 17:02 UTC to May 21, 2013, 17:33 UTC; 5) June 21, 2013 to June 24, 2013; 6) August 19, 2013 to August 22, 2013. From September 18, 2013 to March 17, 2014 the NS HV for the BP and/or LG sensor was shut down 6 times: 1) for approximately two hours on October 25, 2013; 2) October 28, 2013, 16:00 UTC to October 29, 2013 02:00 UTC; 3) For less than an hour on November 5, 2013; 4) For less than an hour on December 14, 2013; 5) December 26, 2013 07:00 UTC to December 31, 2013 20:00 UTC; 6) For less than an hour on Jan 25, 2014. Quality and Limitations : This data set has been processed as described in the 'MESSENGER Neutron Spectrometer (NS) EDR-to-CDR-to-DDR Processing' document. All data have been successfully processed through the NS data processing codes and all data are found to be nominal. Other than the scheduled 'instrument off' periods described above, no data gaps or corrupted data have been identified for any of the NS operational periods. Although there may be some data not identified as missing or corrupted, such data should be minimal and a very small fraction of the available data. Regarding data quality, the primary factor that affects the quality of the NS data are solar particle events. The table below lists the times during the data delivery period where it was determined that there were fluxes of solar energetic particles high enough to affect the data background. The columns of the table are: Name (numeric label for the solar particle event); start time in UTC indicating the starting time of the solar particle event; stop time in UTC indicating the stopping time of the solar particle event; type (All stands for all sensors, LG1 or LG2 stands for lithium glass sensor 1 or 2 only; BPS stands for borated plastic scintillator only). Name Start Time End Time Type ------------------------------------------------------------ 001 03/24/2011 11:48:19 03/24/2011 18:50:03 All 002 03/25/2011 05:52:23 03/25/2011 10:15:36 All 003 03/25/2011 23:01:18 03/26/2011 04:28:38 LG2 004 03/30/2011 17:00:00 03/30/2011 22:00:00 All 005 04/04/2011 09:48:40 04/04/2011 13:56:56 LG2 006 05/24/2011 22:00:00 06/03/2011 03:45:00 All 007 06/04/2011 06:13:13 06/10/2011 22:00:00 BPS 008 06/04/2011 06:13:13 06/12/2011 07:00:00 LG1 009 06/04/2011 06:13:13 06/15/2011 22:00:00 All 010 08/02/2011 05:39:24 08/02/2011 18:24:21 All 011 08/04/2011 03:33:28 08/05/2011 17:00:00 All 012 08/09/2011 07:00:00 08/10/2011 03:00:00 All 013 09/05/2011 05:39:00 09/08/2011 14:00:00 LG2 014 09/06/2011 04:45:00 09/06/2011 07:10:00 BPS 015 09/07/2011 04:01:00 09/07/2011 06:32:00 BPS 016 09/07/2011 18:58:00 09/08/2011 06:00:00 BPS 017 09/08/2011 22:20:00 09/10/2011 02:00:00 All 018 09/22/2011 11:25:40 09/24/2011 08:00:00 All 019 10/04/2011 12:53:49 10/06/2011 02:55:42 All 020 10/14/2011 12:56:57 10/15/2011 10:13:16 All 021 10/17/2011 08:10:30 10/17/2011 11:38:16 LG2 022 11/03/2011 22:50:16 11/06/2011 02:00:00 All 023 11/09/2011 12:56:40 11/09/2011 18:45:00 All 024 11/17/2011 20:52:37 11/18/2011 16:50:00 All 025 12/14/2011 14:20:00 12/14/2011 22:30:00 All 026 12/25/2011 17:48:00 12/26/2011 15:55:00 All 027 01/02/2012 14:54:00 01/03/2012 13:50:00 All 028 01/23/2012 05:36:00 02/06/2012 00:01:00 All 029 03/03/2012 20:11:00 03/17/2012 00:00:00 All 030 04/05/2012 21:13:05 04/06/2012 00:14:30 All 031 04/09/2012 11:04:13 04/09/2012 17:17:43 All 032 04/26/2012 08:25:36 04/26/2012 12:10:43 All 033 04/27/2012 16:00:00 04/28/2012 02:58:00 All 034 05/17/2012 02:32:33 05/19/2012 02:37:40 All 035 05/26/2012 20:16:48 05/30/2012 02:42:00 All 036 06/28/2012 16:04:00 06/29/2012 17:00:00 All 037 07/01/2012 18:58:00 07/02/2012 02:00:00 All 038 07/02/2012 10:18:10 07/02/2012 18:09:00 All 039 07/03/2012 03:03:15 07/03/2012 11:04:13 All 040 07/12/2012 16:26:11 07/14/2012 19:30:00 All 041 07/17/2012 17:00:00 07/21/2012 02:00:00 All 042 07/23/2012 03:52:00 07/29/2012 12:00:00 All 043 07/30/2012 18:34:28 07/30/2012 21:59:08 All 044 07/31/2012 21:47:30 08/01/2012 03:00:00 All 045 09/08/2012 11:14:27 09/08/2012 17:33:04 All 046 09/19/2012 10:48:00 09/25/2012 02:00:00 All 047 09/28/2012 09:50:00 10/01/2012 02:00:00 All 048 10/08/2012 12:22:25 10/09/2012 09:52:50 All 049 10/14/2012 00:30:30 10/14/2012 20:27:11 All 050 10/23/2012 02:57:19 10/23/2012 03:27:48 All 051 10/26/2012 11:29:47 10/26/2012 19:51:10 All 052 11/08/2012 01:45:18 11/08/2012 09:47:18 All 053 11/18/2012 03:33:20 11/18/2012 10:06:41 All 054 11/21/2012 13:42:49 11/22/2012 03:54:25 All 055 02/05/2013 08:10:15 02/05/2013 11:09:20 All 056 03/15/2013 17:58:39 03/17/2013 04:40:28 All 057 04/11/2013 05:52:06 04/13/2013 02:12:05 All 058 04/21/2013 06:33:02 04/23/2013 02:00:00 All 059 04/24/2013 21:13:05 04/26/2013 12:00:00 All 060 04/27/2013 21:43:47 04/28/2013 02:06:58 All 061 04/28/2013 12:10:43 04/28/2013 14:59:34 All 062 05/10/2013 18:34:28 05/11/2013 02:00:00 All 063 05/13/2013 15:30:16 05/14/2013 13:37:42 All 064 05/15/2013 03:28:50 05/15/2013 05:16:17 All 065 05/31/2013 19:40:00 06/01/2013 02:37:40 All 066 06/21/2013 03:08:22 06/25/2013 02:00:00 All 067 08/19/2013 22:29:50 08/22/2013 22:00:00 All 068 10/05/2013 06:27:55 10/07/2013 22:00:00 All 069 10/11/2013 06:33:02 10/16/2013 05:16:17 All 070 10/20/2013 06:02:20 10/20/2013 13:01:53 All 071 10/22/2013 20:32:00 10/23/2013 20:37:16 All 072 10/25/2013 07:29:00 10/27/2013 12:00:00 All 073 10/28/2013 04:09:00 10/31/2013 12:00:00 All 074 11/02/2013 04:35:00 11/03/2013 06:00:00 All 075 11/04/2013 05:46:00 11/05/2013 04:25:00 All 076 11/05/2013 21:43:00 11/05/2013 23:01:00 All 077 11/07/2013 10:48:00 11/09/2013 22:00:00 All 078 11/19/2013 09:57:00 11/21/2013 12:00:00 All 079 11/29/2013 03:59:00 11/29/2013 20:07:00 All 080 11/30/2013 02:37:00 12/02/2013 03:23:00 All 081 12/05/2013 11:34:00 12/05/2013 20:53:00 All 082 12/13/2013 20:06:00 12/15/2013 12:00:00 All 083 12/26/2013 03:13:00 12/31/2013 22:00:00 All 084 01/06/2014 07:19:05 01/11/2014 22:00:00 All 085 01/22/2014 03:59:32 01/23/2014 07:00:00 All 086 01/27/2014 22:00:00 01/31/2014 05:52:00 All 087 02/11/2014 03:03:15 02/11/2014 21:02:00 All 088 02/12/2014 06:07:27 02/12/2014 12:10:00 All 089 02/14/2014 15:45:00 02/15/2014 12:32:00 All 090 02/18/2014 00:29:45 02/19/2014 04:00:00 All 091 02/20/2014 07:00:00 02/21/2014 06:00:00 All 092 02/25/2014 03:44:11 03/05/2014 06:00:00 All 093 03/14/2014 21:28:00 03/14/2014 12:00:00 All It has been determined that the deadtime correction for nominal solar quiet conditions is minimal and is therefore not being applied. Deadtime remains an important uncorrected effect for periods of intense solar activity. However, those periods of intense solar activity, which are listed above, do not provide valid planetary data and are not used in the normal planetary data processing.
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| CITATION_DESCRIPTION |
D. J. LAWRENCE (APL), MESSENGER E/V/H GRNS 4 NEUTRON SPECTROMETER DDR V1.0, MESS-E/V/H-GRNS-4-NS-DDR-V1.0, NASA Planetary Data System, 2013.
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| ABSTRACT_TEXT |
Abstract : This data set consists of the MESSENGER Neutron Spectrometer (NS) 'derived' data records (DDRs). The NS experiment is a neutron spectrometer designed to observe neutrons emitted from Mercury's surface in the energy range from 0.01 eV to 7 MeV. There is 1 NS DDR standard data product (Neutron Count Rate, NS_DDR_NCR) and 1 NS DDR special data product (Neutron Composition, NS_DDR_NCP). The NCR data products contain net neutron count rates from the LG1, LG2, and BP sensors and uncertainties from each of these sensors. The NCP data product contains fast and epithermal count rates as a function of latitude, along with simulated count rates for the cases of no hydrogen and for a thick layer of 100 wt. percent water ice in all radar bright regions.
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| PRODUCER_FULL_NAME |
DAVID LAWRENCE
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| SEARCH/ACCESS DATA |
Geosciences Web Services
Mercury Orbital Data Explorer
Geosciences Online Archives
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