220
Chapter 23
single particles. Thus, from the measurements alone, it is impossible to draw
other than qualitative conclusions. Phase curves of snow had been measured
earlier by Knowles Middleton and Mungall (1952). The smallest phase angle
in their measurements was 2 degrees. The measurements have been studied
in depth by Veverka (1970, 1973), and Verbiscer and Veverka (1990). The
main result is obvious: snow scatters light according to Lambert’s law at
large phase angles. The results agreed well with those obtained by space
probes for icy satellites of the solar system. The reflectance and
transmittance of snow have been further studied, e.g., by Kimball and Hand
(1930), Gerdel (1948), Dunkle and Bevans (1955), and Hyvärinen and
Lammasniemi (1987). These studies were mostly carried out to estimate the
melting of the snow cover. However, they also include basic information on
different types and grain sizes of snow.
The measurements indicate the presence of an opposition spike, which
behaves like that for the icy moons (e.g., Lockwood et al. 1980) and Saturn’s
rings (e.g., Franklin and Cook 1965). The opposition spike of snow is
qualitatively similar to that of the high-albedo asteroids (44) Nysa (Harris et
al. 1989) and (64) Angelina (Poutanen 1983).
In what follows, we describe the device used for the measurements of
snow, and present the results of the three measuring campaigns carried out in
1979-81 (I), 1995 (II), and 1997 (III).
2.
DEVICE FOR SNOW MEASUREMENTS
The first set of field measurements of snow and snowballs (campaign I)
were measured in 1979-81 (Piironen 1994) by making use of a device
designed at the Department of Astronomy, University of Oulu. Finland
(Figure 1). The mechanical part of the system was built at the workshop of
the Department of Physics, University of Oulu, and the photometer and the
strip chart recorder were the instruments used for the photometry of
planetary objects at the Aarne Karjalainen Observatory, Kiiminki.
Chapter 23
single particles. Thus, from the measurements alone, it is impossible to draw
other than qualitative conclusions. Phase curves of snow had been measured
earlier by Knowles Middleton and Mungall (1952). The smallest phase angle
in their measurements was 2 degrees. The measurements have been studied
in depth by Veverka (1970, 1973), and Verbiscer and Veverka (1990). The
main result is obvious: snow scatters light according to Lambert’s law at
large phase angles. The results agreed well with those obtained by space
probes for icy satellites of the solar system. The reflectance and
transmittance of snow have been further studied, e.g., by Kimball and Hand
(1930), Gerdel (1948), Dunkle and Bevans (1955), and Hyvärinen and
Lammasniemi (1987). These studies were mostly carried out to estimate the
melting of the snow cover. However, they also include basic information on
different types and grain sizes of snow.
The measurements indicate the presence of an opposition spike, which
behaves like that for the icy moons (e.g., Lockwood et al. 1980) and Saturn’s
rings (e.g., Franklin and Cook 1965). The opposition spike of snow is
qualitatively similar to that of the high-albedo asteroids (44) Nysa (Harris et
al. 1989) and (64) Angelina (Poutanen 1983).
In what follows, we describe the device used for the measurements of
snow, and present the results of the three measuring campaigns carried out in
1979-81 (I), 1995 (II), and 1997 (III).
2.
DEVICE FOR SNOW MEASUREMENTS
The first set of field measurements of snow and snowballs (campaign I)
were measured in 1979-81 (Piironen 1994) by making use of a device
designed at the Department of Astronomy, University of Oulu. Finland
(Figure 1). The mechanical part of the system was built at the workshop of
the Department of Physics, University of Oulu, and the photometer and the
strip chart recorder were the instruments used for the photometry of
planetary objects at the Aarne Karjalainen Observatory, Kiiminki.