Supraglacial debris thickness data from Ngozumpa Glacier, Nepal
This repository contains:
2 files of measurements of supraglacial debris thickness at two sites (Gokyo and Margin) on the surface of the Ngozumpa Glacier (27°57′N, 85°42′E), Nepal, made using ground penetrating radar (GPR)
1 file of supplementary supraglacial thickness measurements from additional glacier sites using various methods
All files are comma separated text files
Description of Ngozumpa GPR data:
GPR measurements were made between 31st March and 20th April 2016.
Debris thickness was sampled in 36 individual radar transects, covering sloping and level terrain with coarse and fine surface material. The GPR system was a dual frequency 200/600MHz IDS RIS One, mounted on a small plastic sled and drawn along the surface.
Data were collected to a Lenovo Thinkpad using the IDS K2 FastWave software.
The 200 and 600 MHz antennas have separation distances of 0.230 m and 0.096 m respectively.
Data acquisition used a continuous step size, a time window of 100 ms and a digitization interval of 0.024 ns.
The location of the GPR system was recorded simultaneously at 1 s intervals by a low precision GPS integrated with the IDS which assigns a GPS location and time directly to every twelfth GPR trace, and by a more accurate differential GPS (dGPS) system consisting of a Trimble XH and Tornado antenna mounted on the GPR and a local base station of a Trimble Geo7X and Zephyr antenna.
Radargrams were processed in REFLEXW (Sandmeier software)
The reflection at the ice surface was picked manually wherever it was clearly identifiable and was not picked if it was indistinct.
The appropriate signal velocity for the supraglacial debris was obtained by burying a 1.5 m long steel bar to a known depth and then passing the GPR over the buried target and picking the two-way travel time to its reflection. Both fine and coarse material gave similar wave speeds (0.15 and 0.16 m ns-1), the average of which was used for all the radar lines measured
Description of supplementary data:
C1: Ngozumpa glacier (Nepal) about 1km from the terminus, measured using a theodolite survey (Nicholson and Benn, 2012)
C2: Ngozumpa glacier (Nepal) about 7km from the terminus, measured using a theodolite survey (Nicholson and Benn, 2012)
C3: Ngozumpa glacier (Nepal) about 3km from the terminus, measured using a photogrammetric survey (Nicholson and Mertes, 2017)
C4: Lirung glacier (Nepal), measured with GPR (McCarthy and others 2016)
C5: Suldenferner (Italy), measured with GPR (del Gobbo, 2017)
C6: Suldenferner (Italy), measured by excavation of debris (del Gobbo, 2017)
C7: Arolla glacier, (Switzerland), measured by excavation of debris (Reid and others, 2012)
Details of these datasets can be found in the following publications:
Nicholson, L. I. and Benn, D. I.: Properties of natural supraglacial debris in relation to modelling sub-debris ice ablation, Earth Surf. Process. Landforms, 38(5), 409–501, doi:10.1002/esp.3299, 2012.
Nicholson, L. I. and Mertes, J. R.: Thickness estimation of supraglacial debris above ice cliff exposures using a high-resolution digital surface model derived from terrestrial photography, J. Glaciol., 1–10, doi:10.1017/jog.2017.68, 2017
McCarthy, M., Pritchard, H. D., Willis, I. and King, E.: Ground-penetrating radar measurements of debris thickness on Lirung Glacier, Nepal, J. Glaciol., 63(239), 534–555, doi:10.1017/jog.2017.18, 2017.
del Gobbo, C.: Debris thickness investigation of Solda glacier, southern Rhaetian Alps, Italy: Methodological considerations about the use of ground penetrating radar over a debris-covered glacier. MSc Thesis, University of Innsbruck, 2017.
Reid, T. D., Carenzo, M., Pellicciotti, F. and Brock, B. W.: Including debris cover effects in a distributed model of glacier ablation, J. Geophys. Res., 117(D18), 1–15, doi:10.1029/2012JD017795, 2012.