the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Brief communication: RADIX (Rapid Access Drilling and Ice eXtraction) dust logger test in the EastGRIP hole
Abstract. The RADIX (Rapid Access Drilling and Ice eXtraction) optical dust logger is part of the exploratory drilling system developed at the University of Bern. It was previously untested because no RADIX borehole reached to the depth of the required bubble-free ice. In June 2023, we tested the logger with an adapter for the large EastGRIP (East Greenland Ice-core Project) deep borehole. An excellent dust record was obtained for the Bølling-Allerød-Younger Dryas-Early Holocene period. The light scattered by the dust in the ice around the borehole was slightly higher than the detection range of the logger, requiring a reduction in the sensitivity for future deployments.
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RC1: 'Comment on egusphere-2024-372', Ryan Bay, 18 May 2024
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Schwander et al. give a note showing some tantalizing results using a dust logger in the EastGRIP, Greenland borehole. The RADIX dust logger principle and design are partly based on our tools, and I'm delighted to see these results.
The RADIX logger was intended for use in small RADIX boreholes. For this work the tool was fitted with adapters for use in the much larger EastGRIP borehole. Part of innovation of the RADIX drill system is the very narrow 2 cm borehole, resulting in greater mobility and reduced drilling fluid. This compact design places fairly severe space constraints on borehole instruments.
The RADIX design uses a light source which is less focused and canted downward, departing from a tight focus directed sidewise. The PMT detector has a limited acceptance angle, and the authors deem the depth resolution of the tool to be ~20 cm based on the intersection of the source-receiver focus cones. Judging from Figure 3 the resolution may be better than this. This geometry also potentially impacts the dynamic range of the logger over greatly varying polar dust concentrations, and Schwander et al. have considered this including use of simulations. In the cleanest Antarctic ice, the effective scattering length can be tens of meters from AMANDA/IceCube, so this geometry might be less effective there. In a narrow RADIX borehole, fluid drag and logging speed might also pose issues.
A reader is left wanting to see more data than the four meters of logger-core comparison shown in Figure 3, perhaps over a greater depth range.
At Summit, Greenland in the GISP2/GRIP boreholes, we found that bubbles had not completely converted to clathrates and disappeared until below 1600 m. So I wonder if the ice depths at EastGRIP where these logger measurements were made are 100% bubble-free. Dust logging in bubbly ice is achievable (ref. 1), but more dependent on conditions and less easy to interpret than clear ice.
Citation: https://doi.org/10.5194/egusphere-2024-372-RC1 -
RC2: 'Comment on egusphere-2024-372', Matthias Hüther, 02 Jul 2024
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General comments:
Schwander et al. presents first data from a new dust logger designed for narrow boreholes. The test was conducted in a larger borehole as designed, forcing the use of an adapter, and in a different location (Greenland) with higher dust concentration compared to the intended operating area in Antarctica. The report focuses on the evaluation of the optical dust measurement of the scattering from dust particles, as the scattering from bubbles saturates the sensitivity range. Therefore, it does not allow the measurement of dust absorption from dust in non-bubble free ice.
The novelty of the design is the miniaturisation of the logger, which allows it to be used in smaller boreholes, and the change from a downward-facing PMT to a side-facing instrument. This first test shows promising results, which seem to require some adjustments to the sensitivity range and the borehole adapter.
The article should be published as it presents a test of a new instrument for in situ measurements in boreholes and its results. The description is well explained, but could go into more detail about the selected components and simulation/correction parameters.
Specific comments:
From line 51 onwards, a correction factor of 0.017 is introduced for the "geometrical transmission", which was not taken into account in the previous work.
Could you specify all the parameters that are now taken into account? For example, does this factor include the mentioned refraction? Does it vary with the type of drilling fluid and the angle of installation in the borehole adapter and/or the tilt in the borehole caused by the eccentrically mounted cable (shown in Figure 1)?
The logger signal shown in Figures 2 and 3 are plotted against borehole depth. Since Rongen (2020) has shown an optical anisotropy in ice, would switching to a directional optical measurement not require the addition of the orientation as a relevant dimension?
Rongen (2020) - Martin Rongen, Ryan Carlton Bay, and Summer Blot The Cryosphere, 14, 2537–2543, 2020 https://doi.org/10.5194/tc-14-2537-2020 Observation of an optical anisotropy in the deep glacial ice at the geographic South Pole using a laser dust loggerCitation: https://doi.org/10.5194/egusphere-2024-372-RC2
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