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An automatic snow depth probe (magnaprobe) patented in 1999 (United States Patent 5,864,059, 1999) and produced commercially by Snow-Hydro LLC has now been used to obtain more than a million simultaneous snow depths (up to 140cm) and GPS measurements during a wide range of field validation campaigns. The magnaprobe consists of a ski pole-like rod housing a magnetostrictive device along which a basket and magnet assembly slides. The rod is inserted to the base of the snow, the basket floats on the snow, and when a button is pushed, the distance between rod tip and basket is measured while a position is acquired. The nature of the substrate beneath the snow controls the snow depth accuracy with errors ranging from near zero for hard bases to +5cm in soft vegetation. The Wide Area Augmentation System-enabled GPS provides a position accurate to 2.5m. The probe increases the speed with which a depth and position measurement can be obtained by a factor of 10 compared to measuring with a traditional ruler probe and writing down the results. The highest boost in snow depth measurement efficiency occurs when the distance between measuring locations is kept relatively small (<10m). Magnaprobes have materially improved our ability to evaluate airborne and satellite-based snow depth products and are likely to see continued heavy use over the next decade as efforts to develop satellite systems for monitoring snow remotely are tested in various field settings.

Plain Language Summary We developed an automatic snow depth probe that can measure both depth and position simultaneously. These probes have been used extensively in snow field campaigns. They are accurate to better than 5cm in measuring depth, with the poorer accuracy coming when soft ground under the snow is encountered; they are accurate to about 5m in measuring position. We expect probes like these will continue to be used in field validation campaigns for the foreseeable future.