23. BACKSCATTERING OF LIGHT BY SNOW
227
of incidence and when the material is darkened with the help of boron
carbide. Because the size range of ice crystals inside the snowballs was few
hundreds of micrometers, the opposition spike could be introduced by
surface structure or microstructure of the fractures inside the crystals. Also
we could not measure snow at extremely small phase angles (less than 0.16
degrees), which prevents us from making conclusions of the behavior of the
opposition spike near zero phase angle. We did not measure particle size and
shape distribution, single scattering properties, refractive indices of snow
and boron carbide, or packing density of the target. We took photographs of
the samples, which are accurate enough to allow a rough estimation of the
properties above. The size estimation of the snow crystals is in good
agreement with the study by Hyvärinen and Lammasniemi (1987).
We can conclude that the mechanism that produces the opposition spike
is similar in all the cases above. This conclusion needs further theoretical
considerations to be fully approved, because the comparison between the
integrated brightness of planetary objects and the surface brightness of
laboratory targets should be made cautiously.
An interesting conclusion can be drawn from the measurements: the
opposition spike of snow could be used to determine the properties of
different types of snows. With the help of small-phase-angle observations,
one could determine the accumulation of dust on the snow surface and even
estimate the particle size of pure snow. This could help in estimating the
purity of the snow, and melting rate, and water content of snow. Such
observations could help in estimating snow purity, melting rate, and water
content, which are of great importance for, e.g., agriculture, and for
estimating the purity of fresh water supplies.
5.
ACKNOWLEDGEMENTS
J. Piironen is grateful to Ulla for patience during the instrument
calibration in the 1979-81 campaign. We like to thank Olof Hernius and
Markku Poutanen in helping to measure accurately the baseline during 1995
and 1997 campaigns.
REFERENCES
Capaccioni, F., Cerroni, P., Barucci, M.A. and Fulchignoni, M. (1990) Phase curves of
meteorites and terrestrial rocks: Laboratory measurements and application to asteroids,
Icarus, 83, 325–348.
Dunkle. R.V. and Bevans, J.T. (1955) An approximate analysis of the solar reflectance and
transmittance of a snow cover, Journal of Meteorology, 13, 212–216.
6.
227
of incidence and when the material is darkened with the help of boron
carbide. Because the size range of ice crystals inside the snowballs was few
hundreds of micrometers, the opposition spike could be introduced by
surface structure or microstructure of the fractures inside the crystals. Also
we could not measure snow at extremely small phase angles (less than 0.16
degrees), which prevents us from making conclusions of the behavior of the
opposition spike near zero phase angle. We did not measure particle size and
shape distribution, single scattering properties, refractive indices of snow
and boron carbide, or packing density of the target. We took photographs of
the samples, which are accurate enough to allow a rough estimation of the
properties above. The size estimation of the snow crystals is in good
agreement with the study by Hyvärinen and Lammasniemi (1987).
We can conclude that the mechanism that produces the opposition spike
is similar in all the cases above. This conclusion needs further theoretical
considerations to be fully approved, because the comparison between the
integrated brightness of planetary objects and the surface brightness of
laboratory targets should be made cautiously.
An interesting conclusion can be drawn from the measurements: the
opposition spike of snow could be used to determine the properties of
different types of snows. With the help of small-phase-angle observations,
one could determine the accumulation of dust on the snow surface and even
estimate the particle size of pure snow. This could help in estimating the
purity of the snow, and melting rate, and water content of snow. Such
observations could help in estimating snow purity, melting rate, and water
content, which are of great importance for, e.g., agriculture, and for
estimating the purity of fresh water supplies.
5.
ACKNOWLEDGEMENTS
J. Piironen is grateful to Ulla for patience during the instrument
calibration in the 1979-81 campaign. We like to thank Olof Hernius and
Markku Poutanen in helping to measure accurately the baseline during 1995
and 1997 campaigns.
REFERENCES
Capaccioni, F., Cerroni, P., Barucci, M.A. and Fulchignoni, M. (1990) Phase curves of
meteorites and terrestrial rocks: Laboratory measurements and application to asteroids,
Icarus, 83, 325–348.
Dunkle. R.V. and Bevans, J.T. (1955) An approximate analysis of the solar reflectance and
transmittance of a snow cover, Journal of Meteorology, 13, 212–216.
6.