Liquid water in a snowpack has been recognized for some time as a quantifiable variable of hydrologic significance. It is also important in the interpretation of snowpack microwave remote sensing data. One effective method for measuring the liquid water content of snow is freezing calorimetry. This technique is presented from theory through application including formulations for calculating the percent of liquid water in the snowpack. Silicone oil has been used successfully as the freezing agent. Consistent results can be obtained with the method, even when using newly-trained operators. Liquid water content data can be obtained approximately every 15 minutes when using two calorimeters and three operators. The freezing calorimetric approach was found to be accurate in determining the liquid water content of the snow to within ± 1.0-2.0 percent by weight.
Microwave signatures have been found to be related to variations in snow conditions found on the earth's surface. Most of these observations have been obtained by passive microwave radiometry. In general, inverse relationships between microwave brightness temperature (TB) and snow depth were observed for dry snowpacks. The results from truck-mounted scatterometers indicated that the backscattering cross sections from snowpacks increased with snow depths, also in dry snow conditions. The reported aircraft mission was the first trial in which simultaneous active and passive microwave measurements were made over a wet snowpack. The test site was located in the Colorado Rocky Mountains. The results from this experiment suggest that microwave techniques using both radiometers and scatterometers may be useful in determining snow water equivalent even when the snowpack is wet.
During the winter of 1981 the mean snow covered area in the Northern Hemisphere was less than any other year in the 15-year record (1966-1981) except 1970. For North America, the mean snow cover area was the lowest on record, and for Eurasia the mean snow cover area was the second lowest since records began in 1966. It has been observed that the average winter snow cover in both North America and Eurasia for both 1980 and 1981 decreased from that of the previous year, the first time this has been observed in the 15-year period of record. Assessment of any long term climatic tiends must wait extension of the snow cover data base.
After having been in orbit for less than one year, the Earth Resources Technology Satellite (ERTS‐1) has shown that it provides applicable data for more effective monitoring and management of surface‐water features over the globe. In addition the Data Collection System (DCS) has proved to be a reliable tool for gathering hydrologic data from remote regions.
This symposium was held May 18–19 as part of the International Association of Hydrological Sciences Third Scientific Assembly in Baltimore, Md. Sponsored by the International Committee on Remote Sensing and Data Transmission (ICRSDT), the symposium was well attended, with some sessions having over 100 participants. Five sessions were held, covering the topics of large‐scale processes; evapotranspiration; precipitation; ice, snow, and climate; and remote sensing, with a total of 19 papers presented. All authors were present, and all papers were prepublished as IAHS Publication 186, price $40. In addition, a poster paper session was held.
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