Data Set Information
DATA_SET_NAME MESSENGER H XRS REDUCED DATA RECORD (RDR) MAPS V1.0
DATA_SET_ID MESS-H-XRS-3-RDR-MAPS-V1.0
NSSDC_DATA_SET_ID
DATA_SET_TERSE_DESCRIPTION
DATA_SET_DESCRIPTION Data Set Overview : Each observation is calibrated and processed into the CDR data set and then further processed to produce a map of elemental ratios, the maps of which compose the RDR data set. The orbital mechanics of the instrument and field-of-view of each measurement are accounted for in the products of the elemental ratio maps, and are also a part of the processing that produces the uncertainty map that corresponds to each ratio map. Instrument Overview : The X-Ray Spectrometer (XRS) experiment is comprised of three identical gas proportional counters (GPC) that measure X-rays emitted from the surface of Mercury in the energy range from about 1 to 10 keV. X-rays in this energy range sample the planetary surface to depths of a few tens of microns. See the INSTRUMENT.CAT file for more information and [SCHLEMMETAL2007] for full details. Calibration Overview : The supernova remnant X-ray source Cassiopeia-A (Cas-A) is being used for periodic in-flight calibration because of its relatively high intensity in the XRS energy range. Once or twice a year XRS is pointed to Cas-A for about 48 hours and then away from that source for another 48 hours to accumulate background measurements. These measurements provide an evaluation and calibration of the XRS anti- coincidence and rise-time discrimination background rejection systems. Parameters : The principal parameters when observing with the XRS are as follows: * Integration Period: Normal (quiet Sun) or Flare. In Normal mode three different integration intervals are used, depending on distance to the planet. These may be set over a wide range, but the default values are: Integration Collection Time Closest: 40 s 2000 s Mid-Range: 200 s 10000 s Greatest: 450 s 31200 s In flare mode integration periods are automatically shortened to a pre-determined level, typically 20 s, for 60 minutes or less. * Veto Event: Accept or reject events with a simultaneous signal from the anti-coincidence wires. * Rise-Time Validation: Accept or reject events with an invalid rise time measurement. Data : The XRS instrument telemetry conveys science data, configuration data and status (housekeeping) data. Several telemetry packets are used to downlink this information: Status Housekeeping Packets Uncompressed Science Packets Compressed Science Packets Raw Sensor Data Packets The useful science and housekeeping measurements from the telemetry are decompressed and decomutated and are correlated and accumulated into one binary table, which constitutes the primary experimental data record. Each record of the table contains four energy spectra, housekeeping, status, and rate data for one integration period. The spectra correspond to the Mg-filtered detector (GPC1), the Al-filtered detector (GPC2), the unfiltered detector (GPC3), and the solar monitor (SAX). All the spectra have 256 bins, but only the highest 244 bins for the GPC and the highest 231 bins for the SAX are telemetered. All bins are 16 bits deep. There are five 32-bit rate counters for SAX and nine 24-bit rate counters for each of the three gas proportional counters. Rate counters for all four detectors include raw, valid event, analyzed, pileup, and high-energy rates. The gas detectors also have counters for the veto-anode, veto, rise-pileup, and rise-rejection rates. Housekeeping data provide voltage, current, and temperature readings measured at the end of each integration period. Also reported are record and software status, hardware settings and integration and reporting times. The CDR data products are aggregated to produce the RDRs; in combination with the relevant SPICE kernels and the instrument's field-of-view parameters, a planetary footprint can be calculated for each CDR record. These footprints form the basis for placing CDR data onto the aggregate map that forms the basis of the elemental ratio maps.
DATA_SET_RELEASE_DATE 2016-05-06T00:00:00.000Z
START_TIME 2011-04-07T03:19:53.000Z
STOP_TIME 2015-04-24T09:05:34.000Z
MISSION_NAME MESSENGER
MISSION_START_DATE 2004-08-03T12:00:00.000Z
MISSION_STOP_DATE 2015-04-30T12:00:00.000Z
TARGET_NAME MERCURY
TARGET_TYPE PLANET
INSTRUMENT_HOST_ID MESS
INSTRUMENT_NAME XRAY SPECTROMETER
INSTRUMENT_ID XRS
INSTRUMENT_TYPE XRAY SPECTROMETER
NODE_NAME Geosciences
ARCHIVE_STATUS ARCHIVED - ACCUMULATING
CONFIDENCE_LEVEL_NOTE Confidence Level Overview : The XRS CDR data are the calibrated data records released for the XRS. They include all of the EDR data plus other information such as detector energy calibration, engineering data conversions, and spatial data which will be necessary to convert raw XRS counts to planetary surface compositions. The XRS RDR maps are created using the calibrated XRS CDR products. Review : The XRS CDR was reviewed internally by the XRS team prior to release to the PDS. PDS also performed an external review of the XRS CDR. Likewise, the XRS RDR products are reviewed both internally by the XRS science team and by PDS. Data Coverage and Quality : XRS RDR maps are generated from data collected only while in orbit at Mercury, which is from phases Mercury Orbit through Mercury Orbit Year 5. It is, however, helpful to review the larger mission from which these data are derived. Nineteen mission phases: Launch, Earth Cruise, Earth Flyby, Venus 1 Cruise, Venus 1 Flyby, Venus 2 Cruise, Venus 2 Flyby, Mercury 1 Cruise, Mercury 1 flyby, Mercury 2 Cruise, Mercury 2 flyby, Mercury 3 Cruise, Mercury 3 flyby, Mercury 4 Cruise, Mercury Orbit, Mercury Orbit Year 2, Mercury Orbit Year 3, Mercury Orbit Year 4, and Mercury Orbit Year 5. These mission phases are defined as: Start time End time Phase Name Date (DOY) Date (DOY) ------------------- ----------------- ----------------- Launch 03 Aug 2004 (216) 12 Sep 2004 (256) Earth Cruise 13 Sep 2004 (257) 18 Jul 2005 (199) Earth Flyby 19 Jul 2005 (200) 16 Aug 2005 (228) Venus 1 Cruise 17 Aug 2005 (229) 09 Oct 2006 (282) Venus 1 Flyby 10 Oct 2006 (283) 07 Nov 2006 (311) Venus 2 Cruise 08 Nov 2006 (312) 22 May 2007 (142) Venus 2 Flyby 23 May 2007 (143) 20 Jun 2007 (171) Mercury 1 Cruise 21 Jun 2007 (172) 30 Dec 2007 (364) Mercury 1 Flyby 31 Dec 2007 (365) 28 Jan 2008 (028) Mercury 2 Cruise 29 Jan 2008 (029) 21 Sep 2008 (265) Mercury 2 Flyby 22 Sep 2008 (266) 20 Oct 2008 (294) Mercury 3 Cruise 21 Oct 2008 (295) 15 Sep 2009 (258) Mercury 3 Flyby 16 Sep 2009 (259) 14 Oct 2009 (287) Mercury 4 Cruise 15 Oct 2009 (288) 03 Mar 2011 (062) Mercury Orbit 04 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) Mercury Orbit Year 4 18 Mar 2014 (077) 17 Mar 2015 (076) Mercury Orbit Year 5 18 Mar 2015 (077) 30 Apr 2015 (120) No XRS data were collected during Earth Flyby or Venus 1 Flyby phases. The XRS was on for some of each of the other seventeen mission phases. During these planned operational periods, the XRS functioned nominally and the data quality was good. Specific XRS operational periods were: Start time End time Phase Name Date (DOY) Date (DOY) ----------------- ---------------- ---------------- Launch 30 Aug 2004 (243) 30 Aug 2004 (243) Earth Cruise 07 Feb 2005 (038) 11 Feb 2005 (042) 14 Apr 2005 (104) 14 Apr 2005 (104) 09 Jul 2005 (190) 13 Jul 2005 (194) Earth Flyby No Data Venus 1 Cruise 16 Jan 2006 (016) 13 Feb 2006 (044) 06 Sep 2006 (249) 10 Sep 2006 (253) Venus 1 Flyby No Data Venus 2 Cruise 27 Jan 2007 (027) 31 Jan 2007 (031) Venus 2 Flyby 26 May 2007 (146) 20 Jun 2007 (171) Mercury 1 Cruise 21 Jun 2007 (172) 08 Aug 2007 (220) 17 Aug 2007 (229) 25 Aug 2007 (237) 21 Dec 2007 (355) 30 Dec 2007 (364) Mercury 1 Flyby 31 Dec 2007 (365) 21 Jan 2008 (021) Mercury 2 Cruise 28 Mar 2008 (088) 02 Jun 2008 (154) 11 Jun 2008 (163) 21 Sep 2008 (265) Mercury 2 Flyby 22 Sep 2008 (266) 20 Oct 2008 (294) Mercury 3 Cruise 21 Oct 2008 (295) 19 Nov 2008 (324) 15 Jan 2009 (015) 04 May 2009 (124) 07 May 2009 (127) 17 May 2009 (137) 28 Aug 2009 (240) 01 Sep 2009 (244) 04 Sep 2009 (247) 15 Sep 2009 (258) Mercury 3 Flyby 16 Sep 2009 (259) 29 Sep 2009 (272) Mercury 4 Cruise 22 Jan 2010 (022) 03 Dec 2010 (337) 06 Dec 2010 (340) 03 Mar 2011 (062) Mercury Orbit 04 Mar 2011 (063) 16 Mar 2011 (075) 23 Mar 2011 (082) 07 Mar 2012 (067) 12 Mar 2012 (072) 17 Mar 2012 (077) Mercury Orbit Year 2 23 Mar 2012 (083) 17 Mar 2013 (076) Mercury Orbit Year 3 18 Mar 2013 (077) 17 Mar 2014 (076) Mercury Orbit Year 4 18 Mar 2014 (077) 17 Mar 2015 (076) Mercury Orbit Year 5 18 Mar 2015 (077) 30 Apr 2015 (120) The XRS detectors were on continuously during orbital mission phases except where spacecraft operations (eclipses) and instrument health and safety (temperature and count rate) required some or all of the detectors to be turned off. Details of these off periods and other operational issues may be found in the XRS EDR and CDR data confidence notes. The XRS RDR maps were produced from data collected during the Mercury Orbit, Mercury Orbit Year 2, Mercury Orbit Year 3, Mercury Orbit Year 4, and Mercury Orbit Year 5 mission phases. The maps are for elemental ratios Mg/Si, Al/Si, S/Si, Ca/Si, and Fe/Si. The Mg/Si and Al/Si maps include data acquired both during solar flares and more quiescent 'Quiet Sun' conditions. The dynamic range of Al/Si on Mercury is considerably smaller than that of Mg/Si and the errors on individual quiet sun Al/Si analyses are relatively large. The other three ratio maps all require flare data and as a result the spatial coverage is more spotty. Because of the MESSENGER spacecraft elliptical orbit which achieves periapse over the northern hemisphere, spatial resolution is finer in the northern hemisphere, but coverage is more complete in the southern hemisphere. Three sets of maps are provided for each element ratio: elemental ratio, error, and effective resolution. The maps are 1440 x 720 pixels corresponding to 1/4-degreee pixels in cylindrical projection centered on lat,lon:0,0. Thus, the first column represents longitude :-180 to -179.75 degrees, the bottom row is -90 to -89.75 degrees south latitude, etc. Images are 8-bit. All maps are linearly scaled such that the maximum pixel value (255) corresponds to a maximum value listed in the table below. Thus, to get the actual value from a pixel, one would multiply the pixel values by the maximum pixel value divided by 255. Zero values indicate no data. Mg/Si xrs_map_mg_si_20150424 max : 0.782 xrs_unc_mg_si_20150424 max : 0.149 xrs_res_mg_si_20150424 max : 1957 Al/Si xrs_map_al_si_20150424 max : 0.353 xrs_unc_al_si_20150424 max : 0.084 xrs_res_al_si_20150424 max : 1916 S/Si xrs_map_s__si_20150424 max : 0.147 xrs_unc_s__si_20150424 max : 0.037 xrs_res_s__si_20150424 max : 2697 Ca/Si xrs_map_ca_si_20150424 max : 0.316 xrs_unc_ca_si_20150424 max : 0.077 xrs_res_ca_si_20150424 max : 2695 Fe/Si xrs_map_fe_si_20150424 max : 0.098 xrs_unc_fe_si_20150424 max : 0.028 xrs_res_fe_si_20150424 max : 2894 Data selection criteria for the maps were as follows: FOV:1 or 3 data from the five Mercury Orbit mission phases only. Data which had contributions from charged particles were excluded, based on the count rate around 8 keV due to electron induced fluorescence of the collimator material, as well as derived Mg/Si and Al/Si count ratios, where higher count rate ratios are generally due to electron fluorescence of the Mg and Al filters. To improve statistical precision, quiet-Sun data (Mg/Si and Al/Si maps) were spatially binned such that XRS count rates acquired within a given spatial bin were co-added prior to derivation of elemental ratios. A quiet-Sun measurement was only included in the maps if the statistical uncertainty on Mg/Si was lower than 0.5 (absolute) and that for Al/Si was lower than 0.2. Only a subset of southern quiet-Sun data was included because there was so much coverage in the southern hemisphere, however, a random selection of southern quiet-Sun data from throughout the orbital mission period is included in the maps so as not to introduce any bias. When coverage included many overlapping footprints, footprint measurements that differed by more than 4 sigma from all others were excluded. Limitations : This is a calibrated data set. It includes the data that are received from the spacecraft telemetry as well as calibration information and other ancillary data necessary for data analysis. The XRS RDR maps are created using the calibrated XRS CDR products.
CITATION_DESCRIPTION L. R. Nittler, MESSENGER H XRS REDUCED DATA RECORD MAPS V1.0, NASA Planetary Data System, 2013.
ABSTRACT_TEXT Abstract : This data set consists of the MESSENGER XRS reduced data record observations, also known as RDRs, which are derived from the calibrated data records, CDRs. Each XRS observation results in four X-ray spectra. When an X-ray interacts with one of the four detectors, a charge or voltage pulse is generated. This signal is converted into one of 2^8 (256) channels, which are correlated to energy. Over a commanded integration time period a histogram of counts as a function of energy (channel number) is recorded. The EDRs are the number of events in each channel of the four detectors accumulated over the integration period. Channels above or below the useful energy range of the detectors are not transmitted. The result is three 244-channel GPC histograms and one 231-channel solar monitor histogram, each of which is designated as a single X-ray spectrum. Each observation is calibrated and processed into the CDR data set and then further processed to produce a map of elemental ratios, the maps of which compose the RDR data set.
PRODUCER_FULL_NAME LARRY R. NITTLER
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