News » Environment

Canadian technology marks future of snow studies

Researchers studying how sound waves travel through snow to produce snow property profiles

by

comment

Do you want to push the button?"

The button is red, flat and a bit larger than a poker chip.

Unremarkable visually, it's what the button does that makes me feel honoured by the invitation.

The button engages a switch connected by two wires to a 20-by 30-centimetre circuit board encased in a metal box with a glass cover. The box is secured like an android infant in a cross-country skiing child carrier. A hole in the bottom of the buggy provides an unobstructed 15-centimetre space between the box and the snowpack.

Walking in snowshoes, Nicholas Kinar tows the buggy across a snowy meadow south of Bow Summit on the Icefields Parkway in Banff National Park. Every 10 paces he stops to depress the button. A saucer-sized speaker on the bottom of the unit emits a blast of crackly static, sending a sound wave to penetrate the snowpack. Two-dozen tiny microphones, each the diameter of an aspirin, are mounted on the bottom of the box 10 centimetres from the speaker.

"It sounds like static, but really it's a carefully produced and designed noise," Kinar explained. "The goal of the SAS2 [acronym for System for the Acoustic Sensing of Snow] is to determine snow water equivalent, snow depth and density, as well as snow structural and thermal properties, and to recompose images of snowpack layers."

Similar to a sonar device sending sound waves to the ocean bottom, the loudspeaker sends the noise into the snowpack. The microphones detect the reflections from the snow layers.

"The time of arrival and frequency response of the reflections are then used as inputs to a mathematical model," Kinar continued with rapid-fire enthusiasm. "This mathematical model is a collection of equations that describe propagation of sound waves through snow. By evaluating these equations, I obtain measurements of the physical properties of snow without having to dig into the snowpack."

While Kinar operates the cutting-edge technology, research technician May Guan follows. Inserting a hollow Plexiglas snow tube at the spot where Kinar took his reading (the SAS2 records centimetre-accurate GPS coordinates with each reading), she withdraws a sample from the 80-centimetre-deep snowpack, then weighs it on a hand-held scale to calculate its weight and water equivalency. Daniel Guenther, an undergrad hydrology student visiting from Germany, digs a snow study pit in the same spot. Later in the lab, they will compare the manual measurements with Kinar's SAS2.

For a century, glaciologists, snow hydrologists, climatologists and avalanche professionals have measured snow depth and density the same way — by digging a snow pit and manually examining snowpack layers. Using a snow saw, thermometer, weigh scale, scoop, magnifying glass and ruler, they study snowpack structure, density and temperature, as well as the shapes, sizes and types of snow crystals. While avalanche forecasters and backcountry skiers focus on how the snowpack layers have bonded to determine the likelihood of avalanches, snow hydrologists determine how much freshwater the snowpack will supply to creeks and rivers once it melts.

While FMCW microwave radar (frequency modulated continuous wave, used by police speed-traps) measures snow depth or snow density (but not both) without touching the snowpack, the SAS2 is the first device to determine depth, density, temperature and wetness successfully from one measurement without contact.

"Nobody has been able to do that," Kinar said. "As soon as the shovel comes in contact with the snow, you modify the properties. Using sonar — it's like making a fingerprint without touching the skin on to paper."

Kinar is developing the device as a PhD project with the University of Saskatchewan's Centre for Hydrology. His supervisor, Dr. John Pomeroy, Canada research chair in water resources and climate change, said he recognized quickly that Kinar, 30-ish, is exceptionally intelligent. He approached Kinar about working on novel instrumentation for snow.

After testing several prototypes, Kinar spent many months designing and building the SAS2. The circuit board, consisting of eight ultra-thin layers with the smallest distance between layers being five mil (1 mil equals 1,000th/inch), was manufactured by a specialized facility. Kinar mapped the 120,000 traces, or connections, one by one on a computer. He used a special soldering iron with a tip smaller than one millimetre to attach dozens of surface mount components — ultra-tiny technology used in iPods and cell phones.

"It's been much more difficult than I ever anticipated," Kinar admitted. "It's both a fine art and a science. It certainly gives you more satisfaction when you buy electronics in the store!"

Kinar experimented with many sources to find a lithium battery that could last 12 hours, and function in temperatures as low as minus 40. Employing top-tier FMCW radar, the SAS2 operates at a sampling rate of 2.1 Mhz/second (2.1 million times per second). Results are analyzed in a custom computer program and graphed as an image of the snow cross-section.

"The speaker and microphones are standard stuff," Pomeroy said. "What is special is the computer board, which is more complex than a laptop computer and was custom designed and partly hand built by Nicholas — incredible."

Thus far Kinar has published papers on the earlier prototypes and will soon publish on the SAS2. His presentation at the 2011 American Geophysical Union meeting in San Francisco earned him the organization's prestigious Horton Award. He will present in Banff in June at the 2012 Canadian Geophysical Union Conference.

While the U.S. military employs similar technology for seismic and geological purposes, no-one has yet developed functioning technology to read snow. Current methods include the Swiss-designed snow microbe penetrometer, a digital probe that can send signals to read snowpack properties.

"Penetrometers put a stick into the snow and measure the force it takes to break snow crystal bonds," Pomeroy explained. "The SAS2 uses sound to detect the physical interior of a snowpack, so is close to sonar, but it is a novel application of sonar and geophysical prospecting concepts."

Naturally, such innovative technology would be valuable beyond Canada's borders, said Dr. Danny Marks with the USDA Northwest Watershed Research Centre in Boise, Idaho.

"Sonar monitoring of snow depth has been around for more than a decade, but actually penetrating the snow to estimate mass, density, wetness, etc. is very new," Marks said. "Nicholas should apply for a patent quick, because the U.S. military will certainly be interested and is likely working on similar technology."

Switzerland, as one of the world's few countries where avalanches are socially and economically important, is keenly interested too.

Pomeroy said he's excited about the potential for commercialization. The SAS2 could provide information to be used in models of climate change and snowpack evolution which could help reduce uncertainty in water resources and climate change predictions. As well, the unit can discern strength characteristics and recognize objects such as logs and trees in the snowpack, including eventually, buried avalanche victims.

The next step would be to miniaturize the device so that it would attach to a ski pole and take a reading with every plant, and even be programmed to communicate with a smart phone. It could also be mounted on a robot to cover areas too large for a manual survey.

While the SAS2 is the way of the future, said Pomeroy, "I'm almost a bit sad because I love digging snow pits.

"You get to become one with the snow. You get to feel it, smell it, study the crystals. It's a way of life."

Add a comment