Robotized Inclinometer for Monitoring of Ice Borehole Deformation

Abstract:

Under viscoplastic deformation of ice, the borehole will close or expanded depending on differential pressure on borehole wall. Repeated logging of the borehole inclination and azimuth delivers an estimation of the in-situ deformation within the ice sheet. During years, borehole parameter was periodically measured in many deep holes in Antarctica and Greenland. It is absolutely unknown behavior of the borehole in ice stream area because such observations were never done before. We propose to design robotized inclinometer composed of the surface winch, electronic control system, downhole probe, power supply system and data transmission system for long term borehole field obesearvation at ice stream shear margin. The survey is carried out once-a-day in fully automatic mode. The probe is lowered into the borehole and take borehole tilt measurements with 3D accelerometer/3D magnetometer sensor and temperature measurements with platinum thin-film sensor installed into the nose of the probe. During lowering the probe stopes for one minute in increments of 1 m for thermal stabilization of the temperature sensor. The chamber with inclinometer is perfectly centralized in casing with two sets of jointed arms. The measurements are stored in an intelligent electronic system in the probe. At the end of the measuring phase, using a wireless connection the data are transmitted to a central unit at the top of the borehole. On the surface, a differential GPS system and an automatic weather station are installed. The central unit processes the data and transmits the results to a remote computer using Iridium communication for real-time monitoring and further analysis. The probe electronics is powered by a rechargeable battery which is automatically recharged during the idle state by a contactless induction charging system. The whole system is powered by solar panels, autonomous wind turbine generator and backup battery. The lateral displacements of the borehole are determined by comparing the measured profiles of the borehole obtained within 24 hours of each other. Then in-depth shearing strain rates and stress distribution are estimated.