3-D Characterization of snow crystals utilizing low temperature scanning electron microscopy

The two dimensional shapes of snow crystals have been previously studied and photographed with light microscopes and cameras. Past investigators have been hampered by sublimation and melting of the snow crystal sample and by the limited resolution of the instruments. Better methods for measuring snow crystals are needed for understanding snowpack processes and improving microwave remote sensing of snow. Snow samples from Maryland, West Virginia, Colorado, wyoming, and Alaska have been examined with low temperature scanning electron microscopy (SEM) to produce startling new images of snow crystals. Low temperature SEM avoids problems with sublimation and melting, provides extreme magnification capability, and allows quantitative measurement of snow crystal size and shape with the assistance of 3-D or stereo imaging. The 3-D representations show in stereo several different types of newly fallen or precipitated snow crystals, numerous examples of crystals in different stages of metamorphism from natural snowpacks, and algae and bacterial forms present in a melting snowpack. The techniques for sampling, storing, and transporting snow crystals to the SEM facility are simple and easy to use.