Let it snow: load cells and the white stuff [Updated January 2021]
The first snowfall of 2021 has decorated our part of Berkshire this week. Needless to say it’s made headline news, despite the fact that northern England and Scotland have had it for several days already…) Deep,long-lasting snow is a rare event, and certainly south the the Scottish Highlands, there are very few businesses that depend on British snow for their income.
For other countries, snow is much more part of their economy, and load cells have played their part in helping measure and assess the impact, qualities and properties of snow on all its various forms.
We’ve updated this article to include some research into skiers and avalanches, and also to remind you of our other snow-related articles:
Avalanches and load cells
Avalanches claim around 20 lives a year in the Swiss Alps, and 90% of the victims trigger the fatal avalanche themselves. As a research paper on skier triggering of avalanches notes:
“The skier seems to be a very efficient trigger, despite his small static load. The skier’s impact has to be considered in stability evaluation and avalanche forecasting.”
Load cells were used to update the numerical modelling for the stability index for snow cover.
“The forces induced by a skier (or snowboarder) within the snow cover were measured in situ with load cells for different snow cover conditions and for different load cell (weak layer) depths within the snow cover… The skier’s impact is measured with load cells buried in the snow cover. The dimension of each of the five identical load cells is 0.5 x 0.5 m, giving an area of 0.25 m2, the thickness is 5 cm and the density about 400 kg/m3 … Within the load cell four cantilever type transducers measure the normal and shear force.”
The load cells were placed in position on the surface of the snow just prior to forecast snowfall. Seven days later, almost 60cm of snow had fallen on top. When the skier stepped on the snow above the load cell in their skis, the accumulated snow compacted down to 32cm above the load cell. When the skier did a jumping test, this compacted the snow further to 21cm above the load cell. The team also compared soft snow with no crust, and hard snow with a top crust.
The researchers found that:
“The impact substantially decreases with increasing depth, explaining why triggering points are often observed near rocks or to the margins of a slope, where snow depth is smaller and additionally the snow cover weaker in general.”
Examining microscale snow crystals
To know your snow, you need to understand its 3D structure. At the Luleå University of Technology (LTU) in Sweden, a new x-ray microtomography system has been used to enable 3D in-situ imaging of snow crystals. To examine how the snow crystals responded to compaction, the team needed to measure fresh snow, captured just minutes after it had fallen. A sample bed just 6mm by 5mm was monitored using a load stage with a 500N load cell, maintained at a constant temperature of -15°C.
As Dr Fredrik Forsberg, Associate Senior Lecturer in the Department of Engineering Sciences & Mathematics, explained in an article for Scientist Live:
“Four XMT scans were acquired along the load cycle 0N-10N-18N-25N, at a constant temperature of -15°C. Quantitative analysis of microstructure (shape of crystals, porosity, etc.) was obtained from 3D image analysis … These tools allow us to study the compaction process at multiple spatial scales, global phenomena and grain-to-grain interactions.”
Best foot forward
Load cells have also been used to test snow shoes. Since the whole purpose of snow shoes is to spread the load across the shoe and enable the wearer to walk on deep snow, load cells were used to analyse the force placed on the heel and the toe of the shoe.
Measuring the snow-water-equivalent
The volume of water released when snow melts can be considerable, so being able to calculate the snow-water-equivalent (SWE) can help in the management of water resources and the avoidance of flooding.
‘Snow pillows’ are usually used to measure the SWE of the snow pack, but most of these use anti-freeze, which makes them undesirable for use in remote wildernesses and protected environments. An Austrian company has created a set of environmentally friendly snow scales that use load cells and perforated aluminium plates to measure the SWE accurately, without the need for anti-freeze.
The snow scale is built from seven perforated panels, creating a measuring surface measuring 2.8 metres by x 2.4metres. The perforations prevent the accumulation of water an minimises the temperature differences between scales and ground. As the company brochure explains:
“The measurement is carried out on the centre plate, the surrounding plates serve as a stabilizing zone in order to compensate stress in the snow pack as well as to counteract the problem of ice bridges through the large measuring surface.”
Keeping the lights on
Guess where the snowiest city on earth is – Alaska? Russia? Canada? The answer is Aomori City, in Tōhoku, Japan, with an average annual fall of 312 inches of snow. No wonder the Japanese are interested in using load cells to measure the impact so much snow has on their infrastructure.
In Hokkaido, Fibre optic load cells underwent field trails to measure snow loads on electrical power lines. These were chosen because the cells are not affected by electromagnetic and radio frequency interference (EMI/RFI), can be reliably used at elevated temperatures, and all are suitable for use in wet environments.
Snow us your project
If you have a project that could benefit from our expertise in designing and manufacturing precision load cells, call us. We’re happy to help with any aspect, from initial set-up design to bespoke load cell systems created just for your research or testing requirements.
