Data Set Information
DATA_SET_NAME DAWN GRAND MAP VESTA GAMMA FE UNCORRECTED COUNTS V1.0
DATA_SET_ID DAWN-A-GRAND-5-VESTA-GAMMA-IRON-UNC-V1.0
NSSDC_DATA_SET_ID
DATA_SET_TERSE_DESCRIPTION
DATA_SET_DESCRIPTION Data Set Overview : These tables provide maps of net counting rates of Fe gamma rays at 7.6 MeV measured by the BGO detector of Dawn's Gamma Ray and Neutron Detector acquired at the low altitude mapping orbit. The data are binned on 30 degree equal area pixels. The counting rates are accompanied by their 1-sigma standard errors of the mean and average numbers of 5-deg pixels used to derive the 30-deg counting rates and errors. The counting rates were normalized for variations of live time, solid angle of Vesta, and galactic cosmic ray intensity, but were not corrected for variations of neutron number density. The table contains the original Fe counting rates and errors reported by YAMASHITAETAL2013. The data were acquired during the low altitude mapping orbit (approximately 210 km from the surface) phase (LAMO). Only those when the spacecraft is nadir pointing (less than 5 degrees between the +Z axis of the spacecraft and the center of Vesta) are used to map Fe counting rates. At this altitude, the spatial resolution of the gamma ray spectrometer was about 300 km (PRETTYMANETAL2011). Parameters : Each row of the table provides composition information for a single pixel. The format for each row is '(i10,6(f7.1),2(1x,e13.3)),i10'. East longitude convention is used (-180 to 180 degrees) with Claudia (double prime) coordinate systems. The column description follows: 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 DELTA_LON (F7.1) Width of Pixel in latitude deg 4 MIN_LON (F7.1) Pixel longitude lower boundary deg 5 MAX_LON (F7.1) Pixel longitude upper boundary deg 6 DELTA_LON (F7.1) Width of Pixel in longitude deg 7 FE_COUNTING_RATE (E13.3) Fe counting rate uncorrected count/s for neutron number density 8 SIG_FE_COUNTING_RATE (E13.3) 1-sigma uncertainty in the count/s uncorrected Fe counting rate 9 FE_SAMPLES (I10) Average number of 5-deg pixels per 30-deg pixel used to determine the uncorrected Fe counting rate and uncertainty
DATA_SET_RELEASE_DATE 2013-07-26T00:00:00.000Z
START_TIME 2011-12-08T12:00:00.000Z
STOP_TIME 2012-04-27T12:00:00.000Z
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 4 VESTA
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 a high order data product derived from gamma ray counting data acquired by GRaND in LAMO as described by YAMASHITAETAL2013. The instrument and observation strategy are described by PRETTYMANETAL2011. Review : This data set is in review by NASA Planetary Data System. Data Coverage and Quality : The data set contains a global map of the counting rate of gamma rays emitted from Fe within Vesta's regolith. There are no gaps in coverage. The depth sampled by gamma rays from which Fe gamma rays are provided is a few decimeters (for example, see PRETTYMANETAL2011). Coordinate System: The data were analyzed and mapped in the Claudia coordinate system, in which the prime meridian passes close to a small crater named Claudia. In this coordinate system, the prominent Marcia crater is located at 190E longitude. Maps published by the Dawn Geochemistry Working Group in the literature are presented in the Claudia coordinate system [PRETTYANETAL2012, LAWRENCEETAL2013, PEPLOWSKIETAL2013, PRETTYMANETAL2013, YAMASHITAETAL2013]. Consistent with IAU guidelines, maps of GRaND data in this archive are presented in the 'Claudia Double Prime' (CDP) coordinate system. CDP has the same pole position as Claudia such that latitudes are the same; however, the prime meridian of CDP is shifted by 210 degrees from that of Claudia, passing 20 degrees to the east of Marcia. The coordinate systems are describes in detail by J.-Y. Li in VESTA_COORDINATES_120918.pdf, which accompanies this archive in the DOCUMENTS directory. All of the maps use rectangular pixels with east longitudes within -180 to 180 degrees in the Claudia system. For archiving, the longitudes were converted to CDP as follows: longitude_CDP : longitude_Claudia - 210 degrees. If longitude_CDP is less than -180 degrees, add 360 degrees. For example, if longitude_Claudia : -170 (the location of Marcia crater), then longitude_CDP : -20. Similarly, longitudes in the CDP system can be converted to Claudia as follows: longitude_Claudia : longitude_CDP + 210. If longitude_Claudia is greater than 180 degrees, subtract 360 degrees. Thus, the pixel longitude boundaries, which were tabulated in this archive in the CDP system, can easily be converted back to the Claudia system, in which the data were analyzed, by the user when desired. To further facilitate comparison between the PDS archived maps and those published in the literature, a 'side-by-side' display of each map in the Claudia and CDP systems is included in the accompanying browse file (see BROWSE directory). For further clarification, we note that map pixels in the Claudia system always have MIN_LON < MAX_LON; however, when transformed into the CDP system, not all pixels will meet this condition. For example, in some quasi-equal area maps, the polar pixels have MIN_LON : -180 and MAX_LON : 180 in the Claudia coordinate system. These pixels span 360 degrees in longitude. When transformed to the CDP coordinate system, these pixels have MIN_LON : -30 and MAX_LON : -30, such that MIN_LON : MAX_LON. In addition, for some maps, a portion of the pixels will have MIN_LON > MAX_LON when transformed into the CDP system. To avoid confusion, we included the width of each pixel in longitude as DELTA_LON. For example, for the aforementioned polar pixels, DELTA_LON : 360. Limitations : Assumptions and limitations underlying the analysis of Fe gamma rays within Vesta's regolith are described by YAMASHITAETAL2013. We note that the tabulated values give the range of counting rates of Fe gamma rays, but in order to quantitatively correlate them with the surface Fe abundance, they need to be corrected for variations of number density of subsurface neutrons that excite Fe nuclei and induce Fe gamma-ray emissions.
CITATION_DESCRIPTION Yamashita N., T.H. Prettyman, D.W. Mittlefehldt, M.J. Toplis, T.J. McCoy, A.W. Beck, R.C. Reedy, W.C. Feldman, D.J. Lawrence, P.N. Peplowski, O. Forni, H. Mizzon, C.A. Raymond, C.T. Russell, Dawn GRaND Fe uncorrected counting rate, DAWN-A-GRAND-5-VESTA-GAMMA-IRON-UNC-V1.0, NASA Planetary Data System, 2013.
ABSTRACT_TEXT This data set provides tables of net counting rates of Fe gamma rays at 7.6 MeV measured by the BGO detector of Dawn's Gamma Ray and Neutron Detector acquired at the low altitude mapping orbit. The counting rates are accompanied by their 1-sigma standard errors of the mean and average numbers of 5-deg pixels used to derive the 30-deg counting rates and errors. The counting rates were normalized for variations of live time, solid angle of Vesta, and galactic cosmic ray intensity, but were not corrected for variations of neutron number density. The table contains the original Fe counting rates and errors reported by YAMASHITAETAL2013.
PRODUCER_FULL_NAME NAOYUKI YAMASHITA
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