Monitoring lake ice with acoustic sensors

Monitoring of the thickness and elastic parameters of floating ice on lakes and the sea is of interest in understanding the climate change impact on Alpine and Arctic environments, assessing ice safety for recreational and engineering purposes, studying ice shelves as well as exploring possibilities for the future exploration of the icy crusts of ocean worlds in our solar system. A multitude of geophysical methods exist today to monitor sea and lake ice thickness as well as elastic parameters. Mostly, seismic and radar measurements are used. Both methods have in common that they come with significant logistical effort and expensive equipment. In this study, we present a novel low cost approach using acoustic sensors for ice monitoring.We explored the possibility of using microphones deployed on frozen lakes in the Swiss Alps to monitor the lake ice-thickness using acoustic signals originating from frequently occurring ice quakes. Data were obtained during a three-month-long field campaign at Lake St. Moritz in Switzerland in winter 2021/2022. Three microphone stations were placed on the lake in addition to five conventional seismometers. These seismometers were used to compare the acoustic signals with the seismic ice quake recordings. Additionally, also active-source experiments were conducted using hammer strokes as source, which were used to constrain elastic parameters of the ice.The acoustic recordings of ice quakes allowed us to exploit the unique characteristics of so-called air-coupled waves to determine time-dependent ice thickness curves of Lake St. Moritz for winter 2021/2022 using acoustic data only. Furthermore, the acoustic data allowed us to gain new insights into the ice/air coupling of seismic waves in ice.