The Evaluation of SR-50 for Snow Depth Measurements at Tanggula Area

Snow cover, an important component of the cryosphere, has a profound impact on the surface and atmospheric heat conditions, ecological environment and water resources due to its special characteristics such as high reflectivity, high emissivity and low thermal conductivity. Because of its altitude and topography, the Tibet Plateau becomes the largest region with snow cover in the Northern Hemisphere. Snow cover data commonly used in scientific research is mostly collected by satellite, microwave snow monitoring data or the daily snow depth measurements from meteorological observation stations. These data show a disadvantage of insufficient time resolution when studying the detailed processes of snow cover and the impacts.Ultrasonic snow depth sensor SR-50, developed by Campbell Company, is an advanced observation instrument for snow depth. Using the measurements obtained by SR-50 at Tanggula (TGL) comprehensive monitoring site in the permafrost region on the Tibet Plateau, the evaluation of SR-50 for snow depth measurements is introduced and the characteristics of snow cover in permafrost regions are analyzed.The results indicate that SR-50 shows a very good ability in monitoring the real-time snow depth on different time scales. SR-50 could capture the detailed processes of surface snow cover, and gain real-time snow depth data. The processes of snow falling and melting could be well understood through the varieties of snow depth. The data of snow cover have a very important role in the study of snow cover processes and its impacts on land surface processes in permafrost regions. It shows that surface snow cover appeared in each month throughout the year in the target regions on the Tibet Plateau. The snow covered days mainly concentrated in the winter half year. In February, March, October and November, the number of snow covered days is larger, but in June, July and August it is much smaller. Overall, the snow depth at TGL site is much thinner compared with that of high latitude regions, and the duration of snow cover is much shorter due to the faster melting speed brought by much higher solar radiation. From 2005 to 2008, the instantaneous maximum snow depth of the region is 22 cm and the days with mean daily snow depth below 5 cm accounts for 71.58% of all snow days. In addition, recent raingauge record of solid precipitation is generally much lower than the actual situation because wind and other factors affect its capturing rate. The observations of snow depth by SR-50 provide a valuable dataset for revising the solid precipitation on the Tibet Plateau.