Abstract
ABSTRACTThe detection and monitoring of meltwater within firn presents a significant monitoring challenge. We explore the potential of small wireless sensors (ETracer+, ET+) to measure temperature, pressure, electrical conductivity and thus the presence or absence of meltwater within firn, through tests in the dry snow zone at the East Greenland Ice Core Project site. The tested sensor platforms are small, robust and low cost, and communicate data via a VHF radio link to surface receivers. The sensors were deployed in low-temperature firn at the centre and shear margins of an ice stream for 4 weeks, and a ‘bucket experiment’ was used to test the detection of water within otherwise dry firn. The tests showed the ET+ could log subsurface temperatures and transmit the recorded data through up to 150 m dry firn. Two VHF receivers were tested: an autonomous phase-sensitive radio-echo sounder (ApRES) and a WinRadio. The ApRES can combine high-resolution imaging of the firn layers (by radio-echo sounding) with in situ measurements from the sensors, to build up a high spatial and temporal resolution picture of the subsurface. These results indicate that wireless sensors have great potential for long-term monitoring of firn processes.
Highlights
Firn is the intermediate product created when snow is converted to glacier ice by a combination of compaction and/ or melt–freeze processes
The camp is situated on the North East Greenland Ice Stream (NEGIS), which drains most of the northeastern part of the ice sheet
The ET+ sensors tested here can detect the presence of meltwater within fresh snow, using electrical conductivity sensors in parallel with pressure and temperature sensors
Summary
Firn is the intermediate product created when snow is converted to glacier ice by a combination of compaction and/ or melt–freeze processes. The objectives of firn monitoring are to measure annual accumulation and densification, identify ice lenses and layers, measure temperature and track percolation of water and estimate the volume of meltwater stored in the firnpack (van As and others, 2016). These parameters are critical for the assessment of glacier mass balance (Sørensen and others, 2011; Simonsen and others, 2013; Munneke and others, 2015; Schaller and others, 2016) and accurate dating of ice cores, by estimating annual layer thickness (Vallelonga and others, 2014). Meltwater percolation may be measured via snow forks (Pfeffer and Humphrey, 1998), or time domain reflectometry (Samimi and Marshall, 2017), and radar, seismic or magnetic resonance techniques can be applied to detect and monitor subsurface meltwater (Forster and others, 2014; Machguth and others, 2016; Montgomery and others, 2017; Legchenko and others, 2018) but in situ measurements are difficult to implement
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