Data Set Overview : The Hayabusa spacecraft launched on May 9, 2003, performed an Earth flyby on May 19, 2004, and reached the asteroid 25143 Itokawa in September 2005, spending September through November 2005 at the asteroid. During the mission the Hayabusa Near-Infrared Spectrometer (NIRS) returned 117,937 spectra, including over 80,000 of the asteroid Itokawa. This data set contains the raw NIRS spectra from the entire mission. For the NIRS calibrated spectra, see the PDS data set HAY-A-NIRS-3-NIRSCAL-V1.0.  NIRS is a grating infrared spectrometer with a 64-element indium-gallium-arsenide (InGaAs) linear detector array that covers the wavelength range of 750 - 2250 nm in increments of 24 nm. NIRS carries two types of onboard calibration targets, an incandescent halogen lamp and a light-emitting diode (LED). The basic unit of spectral data for the raw NIRS spectra is the digital number (DN), showing the integrated photon counts during a time-exposure interval. The raw data are originally sampled with 14 bits per channel (0 - 16383 DNs). A DN has a value of approximately 0.565 mV output from the detector preamplifiers when at a gain of 1.08.  NIRS data are taken by stacking a number of sequential sets of light and dark frames at a single spectral measurement. Dark subtraction and data averaging are carried out with the on-board software, and only the dark-subtracted average, standard deviation, minimum, and maximum values for each channel are returned via telemetry. These are included in the FITS spectral tables as four separate columns within a single FITS file. The number of stacked frames is indicated by the STACK_COUNT keyword in the data labels, and also by the keyword STACK in the FITS header. STACK_COUNT, the number of stacked frames, is equal to two to the power of STACK.  For additional information about the NIRS raw data, see Abe et al. (2006) and Kitazato et al. (2008).   Data Organization and File Naming :  The data are organized into directories by target, with the Itokawa data split into four directories by mission phase (Approach, Gatepoint, Home Position, and Touchdown). In addition there are two calibration directories. Within the directories, the data files are in subdirectories by date. The filenames follow the convention nnnnnnnnnn_lvl1_0.fit, where nnnnnnnnnn is the spacecraft time of the image, and lvl1 indicates raw (level-1) data.   References :  Abe, M., Y. Takagi, K. Kitazato, S. Abe, T. Hiroi, F. Vilas, B.E. Clark, P.A. Abell, S.M. Lederer, K.S. Jarvis, T. Nimura, Y. Ueda, and A. Fujiwara, Near-infrared spectral results of asteroid Itokawa from the Hayabusa spacecraft, Science 312, 1334-1338, 2006.  Kitazato, K., B.E. Clark, M. Abe, S. Abe, Y. Takagi, T. Hiroi, O.S. Barnouin-Jha, P.A. Abell, S.M. Lederer, and F. Vilas, Near-infrared spectrophotometry of asteroid 25143 Itokawa from NIRS on the Hayabusa spacecraft, Icarus 194, 137-145, 2008.

Confidence Level Overview : Because Itokawa has a very irregular shape, the NIRS spectral data were acquired under widely varying viewing geometries and lighting conditions. Before comparison with one another, the observed spectra must be photometrically corrected to a common viewing geometry using an accurate photometric function. Otherwise, photometric effects such as phase reddening could be interpreted as spectral variations.