How to measure glacier melting: recent improvements toward real time monitoring

For a hundred years, glaciology researchers have been studying glaciers across the planet to follow their evolution, understand their dynamics and quantify their mass balance. Today, more than 150 glaciers worldwide are being monitored under the patronage of the World Glacier Monitoring Service (WGMS). Over the last few decades, the retreat of glaciers has dramatically accelerated. It is now acknowledged as a strong indicator of the climate change. Measuring glacier melting has therefore gained more and more prominence for assessing the ice mass loss.

This article aims at giving an overview of the most significant onsite methods used by glaciologists to measure glacier melting. A particular emphasis will be placed on the very good results obtained over the last 3 years with the SmartStake station dedicated to the continuous measurement of glacier melting. This latter work has been achieved by A2 Photonic Sensors in close collaboration with the French Institute of Environmental Geosciences (CNRS/IGE).

Beyond the wooden stick: some new technologies bring solutions to measure glacier melting minute by minute

The historical method for measuring glacier melting consists in sticking deeply a wooden stake in the ice and measuring the visible height above the ice surface. This method remains the standard one and is still widely used today. While robust and reliable, the technique turns out to be quite time consuming and expensive: you need to go on site each time you want to measure the melting progress. Consequently, the periodicity of the measurement is low, twice a month at best, with a precision of a few centimeters. By today’s standards, a few measurements per season can’t be sufficient. As a result, researchers started looking for new solutions allowing measuring glacier melting continuously and/or in real time, with increased precision and resolution.

In 2004, Bøggild et al. developed their “Bøggild ablatometer” based on the variation of hydrostatic pressure as the ice surface melts. In 2010, John Hulth developed a clever and direct draw-wire method. More recently, methods based on pressure transducers (Bøggild et al. again in 2017), on thermistor strings (Carturan et al., 2019) and on light sensors (Ialongo et al., 2021) have been developed and tested. For low melting rates or for short occasional measurement campaigns, one can also go with LIDAR or ultrasonic time of flight depth sensors, more often used for snow depth measurements.

All these modern methods are both valuable and relevant and can be discussed in terms of performance, reliability and cost but they all remain research prototypes and, as such, are not easily accessible to the entire glaciology research community. In order to fill this lack of widely available solution, and to provide a solid technical support and maintenance service, the Institute of Environmental Geosciences and A2 Photonic Sensors have developed the SmartStake autonomous station to continuously measure glacier melting with a millimetric precision and a minute resolution.

The SmartStake ice melting monitoring station

The working principle of the SmartStake is based on the draw-wire method, chosen for its simplicity and its robustness. The instrument is to be installed on the glacier surface and is equipped with a rope anchored several meters under the ice surface, associated with an auto-rewind reel. When the glacier melts, its surface goes down and so does the SmartStake, causing the rope to get rewound. A rotary encoder measures automatically the length of rewound rope, which corresponds to the vertical displacement of the SmartStake, hence the cumulative ice melting.

By default, the ice melting measurement is scheduled every 30 minutes, which is usually found sufficient to precisely monitor the melting 24 hours a day. Meanwhile, this time step can be adjusted from 1 minute to several hours if necessary.

To strengthen its analysis capabilities, the SmartStake station is equipped with an external temperature sensor as well as with a snowfall detector allowing for instance the correlation of the melting interruptions with the presence of fresh snow on the glacier surface.  When the glacier is covered by the LoRa network, data can be transmitted in real time and the monitoring can be done from the comfort of your desk. As an illustration, see the online dashboard of our Argentière glacier station. To be honest however, few glaciers have a LoRa coverage strong enough for this purpose. That’s why SmartStake will be embedding a satellite communication feature in the course of 2022, enabling the dissemination of the solution all over the world.

Can an electronic device be as reliable as a robust wooden stake for ice ablation measurement?

Yes, that’s the conclusion of the experiments led over the last 3 years and conducted with two SmartStake prototypes installed by the IGE on the Argentière glacier (France), together with a third one this summer. All 3 units have successfully been measuring glacier melting in a continuous manner during the entire ablation seasons, before hibernating under the snow during the winter and waking up again the next summer, as the snow melts.

During the summer of 2021, the final version of SmartStake was validated in the field. It was installed on the Argentière glacier, at an elevation of 2400m a.s.l., close to another older SmartStake station and to several classical stakes. Results are in perfect match among all instruments. At the same time, a third SmartStake station (granted by the Kilian Jornet foundation as part of its actions toward the preservation of mountains) was made available to the WGMS for an independent evaluation on the Hintereisferner glacier in Austria, at an elevation of 2800m a.s.l. by the Department of Atmospheric and Cryospheric Sciences (ACINN) at the University of Innsbruck, producing very satisfying results, according to Dr. Rainer Prinz, principal investigator of this glacier.

Last but not least, after 3 years in the field and the deployment of 4 SmartStake stations, no damage was reported, even during summer/winter cycles, and results are in keeping with the expectations.

SmartStake and the output of these experiments will be presented at the EGU General Assembly 2022 (May 23-27, 2022). If you cannot attend, please feel free to contact us – we will be happy to discuss your project.