"Ground truth" snow measurements – review of operational and new ground-based snow measurement methods for Sweden, Norway and Finland

Manual snow measurements are becoming increasingly expensive at the same time as climate change imposed snow alterations affects runoff and frost patterns; snow observations are included into runoff modelling, making reliable snow observations outmost important. New and modified ground-based techniques for monitoring snow depth, density, water equivalent (SWE), wetness and layering have the last decade been tested and this justifies a review of such methods. Techniques based on snow mass, electrical properties, attenuation of radioactivity and other miscellaneous properties are reviewed. The following sensors seem suitable for registration of temporal variations: Ultrasonic (depth), several snow pillows at the same location (SWE), CRREL/NRCS weighing sensor (SWE), Snowpower (depth, density, SWE and wetness), active and passive (cosmic) gamma-ray attenuation (SWE), and adjusted TDR-probes (density and wetness). Ground penetrating radar (GPR) is, depending on design and operation mode suitable for different purposes; when arrays of antennas are pulled by a snowmobile the technique is suitable for monitoring of spatial variations in depth, SWE, and density for dry snow. Techniques are under development which will improve the accuracy also for wet snow measurements. Frequency modulated continuous wave (FMCW) GPRs seem fit for measurement of snow layering. Some suggested techniques are not operational yet.Godkänd; 2009; 20090403 (mivu)