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 |
Global map of corrected
thermal+epithermal neutron counting rates measured by the NASA Dawn
mission's Gamma Ray and Neutron Detector from low altitude
[PRETTYMANETAL2017].
|
| 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
|
| SEARCH/ACCESS DATA |
SBN PSI WEBSITE
|
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