Submitted to: Scanning
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 18, 1998
Publication Date: N/A
Interpretive Summary: Snow provides at least one third of the water used for irrigation and the growth of agricultural crops. Predicting the amount of water present in winter snowpack is an essential forecast activity needed to estimate the amount of water that reaches reservoirs and agricultural fields. Because currently used methods for calculating such volumes of water are inaccurate, multimillion dollar losses in agricultural efficiency result each year. Therefore, ARS investigators are developing a new method based upon the examination of snowflakes highly magnified in an instrument called a scanning electron microscope. In the present study, both freshly fallen snowflakes and older snow were placed on special holders that were transferred to a laboratory to examine and compare their magnified images with an ordinary light microscope and with the newer scanning electron microscope. The newer technique provided far greater magnification and clarity of the snow crystals than the ordinary light microscope. Because the new technique yielded accurate measurement of snow particles, it will be used by scientists developing computerized modeling systems for predicting the amount of water in snowpack. These predictive systems will in turn benefit growers who consume irrigation water.
Light (video) microscopy and low temperature SEM were used to examine and record images of identical precipitated and metamorphosed snow and ice crystals. Collection procedures enabled numerous samples from distant locations to be shipped to a laboratory for storage and/or observation. The frozen samples could be imaged with a video microscope in the laboratory at ambient temperatures or with the low temperature SEM. Stereo images obtained by either of these two techniques greatly increased the ease of structural interpretations. The preparation procedures that were used for low temperature SEM did not result in sublimation or melting. However, this technique did provide far greater resolution and depth of focus over that of the video microscope. Greater resolution was especially evident when examining the small particles associated with rime and graupel, whereas the greater depth of focus provided clearer photographs of large crystals such as graupel, depth hoar and ice. Because the SEM images contained only surface information while the video images were frequently confounded by surface and internal information, the SEM images also clarified the structural features of depth hoar and ice crystals