Kaguya Gamma-Ray Spectrometer Corrected Spectra Bundle

This archive contains Kaguya Gamma-Ray Spectrometer (KGRS) corrected and calibrated time-series  spectra and ephemerides, pointing, and geometry (EPG) data for the nominal and extended observation  periods of JAXA's SELENE (Kaguya) mission. The SELENE mission was the Japanese mission to the Moon with a main orbiter “Kaguya” and two daughter relay satellites launched on Sep. 14, 2007. KGRS was mounted on the deck of the main orbiter. It employed a high-purity Ge (HPGe) crystal as a main detector, and surrounding BGO and plastic scintillators as anti-coincidence detectors to reduce backgrounds. The Ge crystal was cooled by a Sterling refrigerator. It made close-proximity observations of the Moon from Dec. 14, 2007 to Dec. 11, 2008 at the high circular orbital altitude of 100 km, and from Feb. 10 to May 28 in 2009 at the low elliptical orbital altitude of ~30 x 50 km. KGRS recorded energy spectra of gamma rays in two gain modes simultaneously; high gain (0.1 to 3 MeV) and low gain (0.1 to 13 MeV), each of which was analyzed by the 13-bit (8192 ch) analog-to-digital converter (ADC). While the former has a higher spectral resolution over the energy range of radioactive elements, the latter has better statistics and covers the whole energy range of major rock-forming elements, including the Fe neutron capture line at 7.6 MeV. The accumulation time of each spectrum was 17 s. Both modes of spectra are included in this archive. The observation epochs of KGRS consists of three regular measurement periods (Period 1 to 3), background measurements, and the annealing of the Ge crystal. The HPGe detector was annealed from 16 to 25, December 2008, which improved energy resolution by a factor of two. Period 1 and 2 lasted two and five months, respectively, with limited spatial or spectral resolutions. Period 3 lasted ~3.5 months (including dead time) with the best spatial and spectral resolutions. In addition, spectra from the background measurement when the satellite was flipped and the detector faced deep space can be analyzed to estimate the background gamma-ray intensity from the satellite due to the exposure to galactic cosmic rays. This archive consists of three spectrum files (each corresponding to one KGRS epoch) and one unified EPG file. The spectrum files contain a time series of corrected and calibrated pulse height spectra acquired by KGRS's HPGe detector in the lunar orbit. In the spectrum files, each row contains the  spacecraft clock (sclk) ticks and UTC time corresponding to the end of the accumulation interval  (17 s), with the two sets of the 8192-channel HPGe spectra accumulated. In the EPG file, each row starts with sclk recorded at the end of the accumulation interval to match spacecraft positions,  pointing, and correction factors with the corrected spectra. Note that the UTC time and ephemeris time included in the EPG file correspond to the midpoint of the accumulation interval. The Kaguya Gamma-Ray Spectrometer Corrected Spectra bundle was created by Naoyuki Yamashita at Planetary Science Institute, AZ, USA, with the permission of JAXA and the KGRS instrument PI Prof. Nobuyuki Hasebe. This work was supported by the NASA under Grant No. NNX16AG54G issued through the Planetary Data Archiving, Restoration, and Tools Program (PDART), Research Opportunities in Space and Earth Sciences (ROSES) 2015.

Tags: kaguya, moon
Organization: National Aeronautics and Space Administration