Abstract
Abstract. The CREST-Snow Analysis and Field Experiment (CREST-SAFE) was carried out during January–March 2011 at the research site of the National Weather Service office, Caribou, ME, USA. In this experiment dual-polarized microwave (37 and 89 GHz) observations were accompanied by detailed synchronous observations of meteorology and snowpack physical properties. The objective of this long-term field experiment was to improve 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 this paper we present an overview of the field experiment and comparative preliminary analysis of the continuous microwave and snowpack observations and simulations. The observations revealed a large difference between the brightness temperature of fresh and aged snowpack even when the snow depth was the same. This is indicative of a substantial impact of evolution of snowpack properties such as snow grain size, density and wetness on microwave observations. In the early spring we frequently observed a large diurnal variation in the 37 and 89 GHz brightness temperature with small depolarization corresponding to daytime snowmelt and nighttime refreeze events. SNTHERM (SNow THERmal Model) and the HUT (Helsinki University of Technology) snow emission model were used to simulate snowpack properties and microwave brightness temperatures, respectively. Simulated snow depth and snowpack temperature using SNTHERM were compared to in situ observations. Similarly, simulated microwave brightness temperatures using the HUT model were compared with the observed brightness temperatures under different snow conditions to identify different states of the snowpack that developed during the winter season.
Highlights
The storage of water in snowpack affects runoff and soil moisture, and is important at the regional scale for various hydrologic applications as flood prediction and water resource management
This paper presents an overview of the CREST-Snow Analysis and Field Experiment (CREST-SAFE) and comparative preliminary analysis of snowpack observations during the 2011 winter season
We expect to measure these parameters regularly and be better able to compare their evolution with SNTHERM. This good overall performance of SNTHERM compared to available measurement of snowpack depth, temperature, and snow grain size and density prompted us to use the simulated SNTHERM time series of snow grain size and density in the HUT microwave snow emission model to conduct a preliminary evaluation of its ability to simulate the observed evolution of microwave brightness temperatures
Summary
The storage of water in snowpack affects runoff and soil moisture, and is important at the regional scale for various hydrologic applications as flood prediction and water resource management. Earlier snow field experiments (Chang et al, 1981; Elder et al, 2009; Hewison and English, 1999; Langlois et al, 2007; Macelloni et al, 2005) have used microwave radiometers to study snowpack microwave emission properties Conducting such experiments is important to improve understanding of the complex influence of different snow characteristics (grain size, density, snow temperature) on the microwave emission and on snow retrievals from microwave measurements. The current experiment builds on earlier studies by extending over the full winter season instead of only one or a few days, allowing processes of snowpack accumulation, metamorphism, and melting – and their impacts on microwave emissivity – to be observed sequentially at the same site The objective of this long-term field experiment was to characterize the behavior of snow-emitted microwave radiation throughout the winter season. The effect of snowpack temperature (related to dry and wet snow conditions) on the microwave brightness temperature has been examined and interpreted
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