Data Set Information
DATA_SET_NAME DAWN GRAND MAP CERES TPE NEUTRON COUNTS V1.0
DATA_SET_ID DAWN-A-GRAND-5-CERES-TPE-COUNTS-V1.0
NSSDC_DATA_SET_ID
DATA_SET_TERSE_DESCRIPTION
DATA_SET_DESCRIPTION Data Set Overview : A global map of thermal+epithermal counting rates measured in a low altitude mapping orbit around Ceres is provided as an ASCII table. The map data are given for twenty-degree, quasi-equal-area pixels. The data reduction and analysis methods are presented in the Supplement of PRETTYMANETAL2017. The thermal+epithermal map data given here appear in Fig. 1 of the main text of PRETTYMANETAL2017. Neutrons in the thermal and epithermal energy range can be captured by Lithium-6 in the lithium-loaded glass scintillator, which is part of the +Z phoswich on GRaND. The reaction produces a light output of approximately 260 keV (electron equivalent energy), which produces a peak in the spectrum of the +Z phoswich (CAT1). The net peak area was extracted to produce a time series of the thermal+epithermal neutron interaction rate. The time series was corrected for variations in the intensity of galactic cosmic rays and the solid angle subtended by Ceres at the spacecraft. Bad data and data not meeting pointing requirements were excluded from the analysis. The data were binned at the subsatellite point on 20-degree quasi-equal area pixels. For each pixel, the mean counting rate and the statistical uncertainty in the mean is reported along with the number of times the pixel was sampled. Parameters : Each row of the table gives the thermal+epithermal counting rate for a single rectangular pixel. The format for each row is '(I10,4(F7.1),2(E14.4),I10)'. East longitude convention is used (-180 to 180 degrees). Each pixel spans a separate and unique portion of Vesta's surface, and together, the pixels provide full global coverage. The BROWSE directory displays the data as a global map. The column descriptions follow: COLUMN NAME FORMAT DESCRIPTION UNITS 0 PIXEL_INDEX (I10) N/A 1 MIN_LAT (F7.1) Pixel latitude lower boundary deg 2 MAX_LAT (F7.1) Pixel latitude upper boundary deg 3 MIN_LON (F7.1) Pixel longitude lower boundary deg 4 MAX_LON (F7.1) Pixel longitude upper boundary deg 5 TPE_COUNTING_RATE (E14.4) Mean thermal+epithermal rate counts/s 6 SIG_TPE_COUNTING_RATE (E14.4) Uncertainty in the mean counts/s 7 TPE_SAMPLES (I10) Number of samples
DATA_SET_RELEASE_DATE 2017-09-25T00:00:00.000Z
START_TIME 2015-12-16T12:00:00.000Z
STOP_TIME 2016-05-11T12:00:00.000Z
MISSION_NAME DAWN MISSION TO VESTA AND CERES
MISSION_START_DATE 2007-09-27T12:00:00.000Z
MISSION_STOP_DATE 2017-06-30T12:00:00.000Z
TARGET_NAME 1 CERES
TARGET_TYPE ASTEROID
INSTRUMENT_HOST_ID DAWN
INSTRUMENT_NAME GAMMA-RAY AND NEUTRON DETECTOR
INSTRUMENT_ID GRAND
INSTRUMENT_TYPE GAMMA RAY SPECTROMETER
NEUTRON SPECTROMETER
NODE_NAME Small Bodies
ARCHIVE_STATUS
CONFIDENCE_LEVEL_NOTE Confidence Level Overview : The data set is an intermediate data product from which hydrogen concentrations were determined [PRETTYMANETAL2017]. Review : This data set is in review by NASA Planetary Data System. Data Coverage and Quality : The data set contains a global map of thermal+epithermal counting rates. There are no gaps in coverage. Thermal+epithermal neutrons are sensitive to the composition of Ceres' regolith to depths up to a few decimeters (for example, see PRETTYMANETAL2011). Coordinate System : The prime meridian is anchored by a small crater called Kait at 2 degrees South [RUSSELLETAL2016]. East longitude convention is used. Limitations : A complete description of data reduction and mapping methods used to create this data set is presented by PRETTYMANETAL2017 (Supplement).
CITATION_DESCRIPTION Prettyman, T.H., Dawn GRaND hydrogen map, DAWN-A-GRAND-5-CERES-TPE-COUNTS-V1.0, NASA Planetary Data System, 2017.
ABSTRACT_TEXT A global map thermal+epithermal neutron counting rates binned on twenty-degree quasi-equal-area pixels is provided. The map was determined from a time series of the rate of neutron capture by lithium in the lithium-loaded glass scintillator, part of the +Z phoswich sensor on Dawn's Gamma Ray and Neutron Detector (GRaND). Neutrons in the thermal and epithermal energy range contribute to the reaction. The data were acquired while in low altitude mapping orbit, about 385 km from Ceres' surface (about 0.8 body radii altitude). Prior to mapping, the time series counting data were subjected to corrections for variations in the flux of galactic cosmic rays and measurement geometry, as described by PRETTYMANETAL2017.
PRODUCER_FULL_NAME THOMAS H. PRETTYMAN
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