Observations of snow crystal shape in cold snowpacks using scanning electron microscopy

Microwave emission from a layer of snow over a ground medium consists of contributions from the snow itself and from the underlying ground. Both contributions are governed by the transmission and reflection properties of the air-snow and snowground boundaries and by the absorption/emission and scattering properties of the snow layer. Presently, a number of microwave algorithms are available to evaluate and retrieve snow cover and snow depth for specific regions and specific seasonal conditions. These algorithms have been derived from research using a combination of microwave sensors on-board satellites, aircraft and trucks, as well as in-situ field studies. However, most of the attention in algorithm development has been directed towards the effects of snow crystal size in scattering microwave energy, but crystal size alone does not account for all of the scattering or energy redistribution. Relatively little effort has been given to the role that crystal shape plays in this regard. The goal of the present study is to determine how both the shape and size of snow crystals affects the response of microwave radiation emanating from below and within the snowpack, and to use this information to produce more reliable snow cover and snow depth algorithms. The lack of precise information about snow crystal size and shape is compensated for by using an average size and an assumed shape in the radiative transfer equations used to calculate energy transfer through the snowpack