  The reflectance of water ice and dust mixtures depends, amongst other
parameters, on how the components are mixed (e.g. intimate mixture, areal
mixture or coating) (Clark et al. 1999). Therefore, when inverting the
reflectance spectra measured from planetary surfaces to derive the amount of
water ice present at the surface, it is critical to distinguish between
different mixing modes of ice and dust. However, the distinction between mixing
modes from reflectance spectra remains ambiguous. Here we show how to identify
some water ice/soil mixing modes from the study of defined spectral criteria
and colour analysis of laboratory mixtures. We have recreated ice and dust
mixtures and found that the appearance of frost on a surface increases its
reflectance and flattens its spectral slopes, whereas the increasing presence
of water ice in intimate mixtures mainly impacts the absorption bands. In
particular, we provide laboratory data and a spectral analysis to help
interpret ice and soil reflectance spectra from the Martian surface.
