snow covered area
depth (m) or water equivalent of snow (mm),
albedo of snow
snow melt (mm/d).
The interpretation of these characteristics is based on the reflectance of
snow which is much larger than the reflectance of other terrain features. In
some cases the reflectance of the soil surface and vegetation are used
together with the snow reflectance in interpretation. Many problems arise
because of the metamorphism of snow and the varying geometry of the Sun -
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Chapter 21
albedo decreases, snow can cover partly or totally the terrain, snow
thickness can vary from a thin layer to its maximum. During winter
several stable phases can exist.
Ablation phase.
Snow surface temperature is zero or below zero and its diurnal variation
can be large, grain size is large, density is high, liquid water exists in
snow, albedo is smaller than in the accumulation phase and is constant
or decreases, snow covers totally or partly the ground but not trees, snow
thickness can vary and snow-less patches on ground can exist. If snowless ground exist its temperature is zero or over zero and it is wet.
During winter a few ablation phases exist.
These three phases and typical snowpack characteristics are presented
with some generalization in Table 1 as follows.
3.
During the stable and ablation phases remote sensing in visible and
infrared regions of electromagnetic spectrum can be used because the
presence of clouds dictates the possibilities to use optical remote sensing
techniques.
2.
PROBLEMS
Information about snow cover are collected for many purposes but in
most cases the following information is needed: