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 31^st March and 20^th 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.