Draw-wire sensor in robust system for ice mass measurements
As a result of global warming, many glaciers are currently retreating and becoming thinner due to increased melting (this is called ice ablation). The two major ice sheets on Earth, those of Greenland and Antarctica, are so large that in practice it is almost impossible to determine the mass balance reliably using conventional methods.
Tracker with draw-wire sensors measures ice ablation of the Sermilik glacier in Greenland
The company Greenland Guidance installed an ice ablation tracker, the DWIAT (draw wire ice ablation tracker), at the location where in 2010 the largest annual melt ever on the Greenland ice sheet was measured. The Sermilik glacier is located in the southern tip of the ice sheet, where temperatures are relatively high in summer and where the ice surface is incredibly dark and absorbs much of the sunlight. Recently, four more DWIATs have been installed on the Russell glacier on the west side of the ice cap.
The special ice ablation trackers use a draw sensor from Althen Sensors & Controls. To measure the ice ablation, deep holes are drilled and the tensile wire is fixed. The units can follow up to 14 m ablation until the wire has to be drilled again. The DWIATs work on solar energy and also follow the ice movement using GNSS positioning. Measurement data is stored locally in the data logger and also sent to the Greenland Guidance data portal.
Measuring with a draw wire sensor
Draw wire sensors (or string pots) are suited for distance and position measurements. They use a flexible cable to measure this distance. Draw wire sensors can measure distances from 50 mm to 50.000 mm and have a very high linearity over the entire measuring range. The pull wire sensor used in DWIAT is the FD115, a robust draw wire sensor, which can withstand temperatures up to -40C.
About Greenland Guidance
Greenland Guidance is a Dutch organization specialized in supporting expeditions and projects in the field of safety, logistics and science in the Arctic. In addition, they build robust scientific instruments.
Situation Sermilik Glacier
Measurements by the automatic weather station network PROMICE indicate that every year 5-6 m of ice melts here - in addition to the snow accumulated in the previous winter - which is a lot compared to other Greenland locations. But in 2010, the QAS_L weather station observed a record-breaking ablation of more than 9 m of ice here - the equivalent of 3 floors of a building!
To investigate the extreme melt at this location, PROMICE entered into a collaboration with the Institute for Marine and Atmospheric Research (IMAU) of Utrecht University. With more instruments that measure the interaction between air and ice on site, the monitoring of ice ablation became even more relevant for the interpretation of data.
That is why Greenland Guidance's DWIAT now measures ablation next to the PROMICE weather station.
With the reference weight drilled 10 m into the ice, this unit recorded the ablation in the summers of 2019 and 2020. In 2019 no less than 7.5 meters of ice ablation was measured, in 2020 "only" 5 meters.