As part of NEAR Earth flyby operations, the Near-Infrared Spectrometer (NIS) instrument field of view was commanded to the center of the Multi-Spectral Imager (MSI) frame (so the two instruments were looking in the same direction) and pointed at a uniform location in Antarctica. Pointing MSI and NIS in the same direction will be a common operational mode at Eros and will enable NIS spectra to be correlated with the higher spatial resolution MSI images. NIS observations of the Earth and Moon are providing crucial space borne calibrations of the instrument in preparation for arrival at Eros. Different geologic materials reflect incoming visible and infrared sunlight to different degrees, depending on mineralogy, grain size, and wavelength of incoming light. NIS will map these differences across the entirety of Eros.

Location
This image is a view of Antarctica from the NEAR MSI. The South Pole is located approximately at the center of the frame. This image is actually a frame from the Earth spin movie, taken about 2.5 hours after the NIS data were acquired. The approximate NIS field of view, or footprint, for Antarctica observations is shown by the rectangle in the frame, and is about 5% the size of the contemporaneous MSI field of view.
 
 
 

Data
This plot shows a preliminary NIS spectrum of Antarctica. This spectrum is derived from over 40 observations using the instrument's narrow slit setting. Error bars are smaller than the dots representing the reflectance values. The major water ice absorptions are clearly visible (see The plot below for reference), as are several absorption bands caused by atmospheric gases and water vapor.
 
 

The NIS observations at Eros will not be complicated, as at Earth, by the presence of an atmosphere which absorbs and scatters light reflected from the surface.  The performance at Earth, however, is illustrative of the instrument's capabilities. As study of the calibration data from the Earth and Moon continue, this performance is expected to improve further.

Laboratory spectrum of water ice is from  T. L. Roush et al. (1990), Icarus 86, pp. 355-382

More Info on the NIS instrument and objectives:
  • NIS Fact Sheet
  • NIS Overview
  • Return to NEAR Homepage

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30 Jan 98