CREST-Snow Analysis and Field Experiment (CREST-SAFE): Continuous In Situ Observations of Snow Physical Properties and Microwave Emission

The CREST-Snow Analysis and Field Experiment (CREST-SAFE) is being carried out for two winter seasons (2011 and 2012) at the research site of the National Weather Service office, Caribou ME, USA. In this ground experiment, dual polarized microwave (37 and 89 GHz) observations are conducted continuously from the time of snow onset to snow melt off along with detailed synchronous observations of snowpack physical properties. The objective of this long term field experiment is to improve our understanding of the effect of changing snow characteristics (grain size, density, temperature) under various meteorological conditions on the microwave emission of snow and hence to improve retrievals of snow cover properties from satellite observations in the microwave spectral range. In this presentation, we give an overview of the field experiment and of routinely automatic and manually measured datasets including: microwave observations (37 and 89 GHz), meteorological observations (air temperature, snow skin temperature, humidity, wind speed and direction, cloud cover, albedo, precipitation, incoming and outgoing radiations), and snow physical parameter from snow pit at different depth (snow depth, grain size, shape, hardness, and density).

We also present the analysis of microwave observations collected during the two years of experiment along with observations of the snowpack properties. Seasonal changes of the snow pack physical properties were simulated with the SNTHERM model whereas to simulate the snowpack emission in the microwave we have used the HUT (Helsinki University of Technology) snow emission model. For different snow conditions simulated microwave brightness temperatures were compared with brightness temperatures observed in situ and with satellite based brightness temperature. The analysis of microwave observations has revealed a large difference in the microwave brightness temperature over fresh and aged snow pack even under the same snow depth. This suggests a substantial impact of other physical parameters on the microwave emission of snow as snow grain size and density.