  We analyse MESSENGER reflectance measurements covering the northern polar
region of Mercury, the least studied region of the northern mercurian
hemisphere. We use observations from the Mercury Dual Imaging System Wide-Angle
Camera (MDIS/WAC) and the Mercury Atmospheric and Surface Composition
Spectrometer (MASCS/VIRS) to study the spectral dependence of the surface
reflectance. The results obtained from the observations made by both
instruments are remarkably consistent. We find that a second degree polynomial
description of the measured reflectance spectra gives very good fits to the
data and that the information that they carry can best be characterized by two
parameters, the mean reflectance and the mean relative spectral slope, averaged
over the explored range of wavelengths. The properties of the four main types
of terrains known to form Mercury's regolith in the northern region, smooth
plains (SP), heavily cratered terrain (HCT), fresh ejecta/materials and red
pitted ground (RPG) are examined in terms of these two parameters. The results
are compared, and found consistent with those obtained by earlier studies in
spite of difficulties met in obtaining accurate reflectance measurements under
the large incidence angle condition characteristic of polar regions. These
results will help with the preparation of the BepiColombo mission and with
supporting its observational strategy.
