e39647f5-fb72-4d16-acbd-9784ed2167b8 eng utf8 dataset dataset NERC EDS UK Polar Data Centre +44 (0)1223 221400 British Antarctic Survey, High Cross, Madingley Road Cambridge Cambridgeshire CB3 0ET United Kingdom polardatacentre@bas.ac.uk https://www.bas.ac.uk/team/business-teams/information-services/uk-polar-data-centre/ information pointOfContact 2025-06-23 ISO 19115 Geographic Information - Metadata ISO 19115:2003(E) European Petroleum Survey Group (EPSG) Geodetic Parameter Registry 2008-11-12 publication European Petroleum Survey Group EPSGadministrator@iogp.org https://www.epsg-registry.org/ EPSG Geodetic Parameter Dataset The EPSG Geodetic Parameter Dataset is a structured dataset of Coordinate Reference Systems and Coordinate Transformations, accessible through this online registry. information publisher urn:ogc:def:crs:EPSG::3031 6.18.3 Raw and processed helicopter-borne radio-echo sounding ice thickness data from the glaciers of the Khumbu Himal, Nepal (2019) 2025-06-23 creation 2025-06-23 revision 2025-06-23 publication 2025-06-23 released 1.0 https://doi.org/10.5285/e39647f5-fb72-4d16-acbd-9784ed2167b8 doi GB/NERC/BAS/PDC/02073 https://data.bas.ac.uk/ NE/L013258/1 award NE/R000107/1 award NE/X005267/1 award Please cite this item as: Pritchard, H., King, E., Goodger, D., Boyle, D., Goldberg, D., Recinos, B., & Orr, A. (2025). Raw and processed helicopter-borne radio-echo sounding ice thickness data from the glaciers of the Khumbu Himal, Nepal (2019) (Version 1.0) [Data set]. NERC EDS UK Polar Data Centre. https://doi.org/10.5285/e39647f5-fb72-4d16-acbd-9784ed2167b8 We present here a new helicopter-borne glacier thickness survey in Khumbu Himal, Nepal, flown by the British Antarctic Survey in 2019. The data consist of raw and processed radio echo sounding radargrams and associated survey measurements acquired using a mono-pulse dipole radar known as 'DELORES', and geolocated glacier thickness interpreted from these radargrams. Mountain glaciers provide an important service in sustaining river flows for large populations downstream of High Mountain Asia, but these glaciers are retreating, and their future is highly uncertain. Glacier thickness measurements are vital for accurate mapping of the remaining ice reserve and for predicting where and how fast it will decline under climate change, but such measurements are severely lacking in this region due to the difficulties of surveying in remote, high-altitude settings. We report on a uniquely extensive new glacier thickness dataset for 17 glaciers in the Khumbu Himal around Everest that our team from the British Antarctic Survey collected using a novel, low-frequency helicopter-borne radar. We succeeded in mapping ice thickness with a precision of around +/-7% for thicknesses of up to 445 m and spanning a total of 119 line-km. This approximately doubles the length of previous thickness surveys in High Mountain Asia. This research is supported by the following NERC fundings: - NERC International Opportunities Fund - Bedmap Himalayas - Reconnaissance (NE/L013258/1) - Polar Expertise - Supporting Development (NE/R000107/1 and NEB1348) - The Big Thaw (NE/X005267/1 and NEB2165) No credit. completed Pritchard, Hamish D. British Antarctic Survey Researcher author King, Edward C. British Antarctic Survey Researcher author Goodger, David J. British Antarctic Survey Researcher author Boyle, Douglas British Antarctic Survey Researcher author Goldberg, Daniel University of Edinburgh Researcher author Recinos, Beatriz University of Edinburgh Researcher author Orr, Andrew British Antarctic Survey Researcher author NERC EDS UK Polar Data Centre +44 (0)1223 221400 British Antarctic Survey, High Cross, Madingley Road Cambridge Cambridgeshire CB3 0ET United Kingdom PDCServiceDesk@bas.ac.uk https://www.bas.ac.uk/team/business-teams/information-services/uk-polar-data-centre/ information pointOfContact asNeeded completed EARTH SCIENCE > Cryosphere > Glaciers/Ice Sheets > Glacier Thickness/Ice Sheet Thickness EARTH SCIENCE > Cryosphere > Glaciers/Ice Sheets > Glacier Topography/Ice Sheet Topography EARTH SCIENCE > Cryosphere > Glaciers/Ice Sheets > Glaciers theme Global Change Master Directory (GCMD) Science Keywords 2026-01-27 publication 23 Global Change Data Center, Science and Exploration Directorate, Goddard Space Flight Center (GSFC) National Aeronautics and Space Administration (NASA) Greenbelt MD United States of America https://earthdata.nasa.gov/about/gcmd/global-change-master-directory-gcmd-keywords Global Change Master Directory (GCMD) Keywords The information provided on this page seeks to define how the GCMD Keywords are structured, used and accessed. It also provides information on how users can participate in the further development of the keywords. information publisher Airborne Glacier Himalayas Radar Thickness theme Khumbu Himal Nepal Upper Dudh Khosi river basin Nepal place Elevation theme GEMET - INSPIRE themes, version 1.0 2021-01-06 revision otherRestrictions no limitations to public access otherRestrictions no limitations license Open Government Licence v3.0 otherRestrictions Data supplied under Open Government Licence v3.0 otherRestrictions None url url crossReference url url largerWorkCitation doi doi crossReference doi doi crossReference doi doi crossReference doi doi crossReference doi doi crossReference url url crossReference doi doi crossReference doi doi crossReference doi doi crossReference doi doi crossReference doi doi crossReference url url dependency url url dependency textTable eng utf8 elevation geoscientificInformation 86.5 87.0 27.83 28.1 2019-10-27 2019-11-06 It is recommended that careful attention be paid to the contents of any data, and that the author be contacted with any questions regarding appropriate use. If you find any errors or omissions, please report them to polardatacentre@bas.ac.uk. NERC EDS UK Polar Data Centre +44 (0)1223 221400 British Antarctic Survey, High Cross, Madingley Road Cambridge Cambridgeshire CB3 0ET United Kingdom PDCServiceDesk@bas.ac.uk https://www.bas.ac.uk/team/business-teams/information-services/uk-polar-data-centre/ information distributor text/csv text/plain application/x-hdf bytes 126701535232 http://ramadda.data.bas.ac.uk/repository/entry/show?entryid=e39647f5-fb72-4d16-acbd-9784ed2167b8 WWW:LINK-1.0-http--link Get Data Download data download bytes 126701535232 http://ramadda.data.bas.ac.uk/repository/entry/show?entryid=e39647f5-fb72-4d16-acbd-9784ed2167b8 WWW:LINK-1.0-http--link Get Data Download data download bytes 126701535232 http://ramadda.data.bas.ac.uk/repository/entry/show?entryid=e39647f5-fb72-4d16-acbd-9784ed2167b8 WWW:LINK-1.0-http--link Get Data Download data download dataset Methodology: A full description of this project can be found in Pritchard et al. (in review). * Airborne survey* We used a wide band mono-pulse dipole radar with a centre frequency of 7 MHz (Pritchard, King et al. 2020) for this survey. Between 27th October and 6th November 2019, we deployed our radar platform to survey the glaciers of Nepal's Khumbu Himal (Everest area) in the upper Dudh Koshi river basin. Our survey flights covered >200 line-km spanning altitudes of 3700 m to 6700 m (Pritchard et al., in review). Based on the findings of Pritchard, King et al. (2020), we designed our survey patterns to include multiple glacier cross profiles because these are less prone to ambiguity between radar returns from the glacier bed and valley side walls. Our flightlines typically followed a continuous zig-zag path with crossings spaced at ~800 m over each glacier trunk for the up-glacier survey limb, with these crossings subsequently linked by a central glacier long-profile on descent. To minimise radar spreading losses, surveys were flown with the radar platform as close as safely possible to the glacier surface, typically a few metres to tens of metres given the considerable roughness of the glacier surfaces in this area. Reaching the highest section of the survey (Everest's Western Cwm), however, required a spiralling rather than direct ascent over the Khumbu Icefall and so achieved multiple glacier crossings at a wider range of ground clearances. To ensure dense radar sampling, we flew these glacier profiles as slowly as was practicable (typically ~10 m s-1 (36 km h-1)). Transit flights to and from the glaciers were at higher speeds of up to ~40 m s-1 (140 km h-1). *Raw radar data * We collected a raw radar data file for each survey flight. The filename format gives the date and time of file creation as yyyymmddhhmmss.hdf5, e.g., 20191103021438.hdf5. File contents: Each file contains two channels of radar data as recorded by the digitiser in the radar receiver system. Channel A is amplified, Channel B unamplified. For each channel, there are multiple Traces, numbered sequentially (e.g., Trace00001). Each trace records a series of radar receiver signed voltages as a measure of returning signal strength. Channel metadata: The total duration of each trace (and therefore its range, in number of samples) is given by the NoOfSamples parameter in the channel metadata. Each sample has a duration of 2 nanoseconds, hence a trace with 10152 samples is 20304 ns long (a range of around 1700 m in ice, or 3000 m in air). The 'SampleRate' parameter gives the timeout time (in seconds) for the receiver to wait to detect a returning pulse before assuming that triggering has failed and moving on to the next set. Each trace represents the averaged voltages of the number of independent radar pulses given by the 'Stacks' parameter. 'Repeats' is an internal system parameter that sets the number of samples to store before writing to disk. The GPS time is recorded along with the corresponding file start and end 'system' times for the onboard computer, to allow the system timestamps to be synchronised to the GPS data in post processing. Trace metadata: In each file, Trace00001 metadata shows the number format (Type) and the precise system date and time (yyyy,mm,dd,hh,mm,ss.ssssss). The 'GGA' string reports the GPS time at completion of this trace as hhmmss.s (e.g., 082520.8) and the GPS position at that time (ddmm.mmmmm, N/S, dddmm.mmmmm, E/W) (e.g., 2748.34269,N,08641.95129,E means 27deg 48.34269' N, 086deg 41.95129' E). A new system time and GPS time and position is then stored for every 1000th subsequent trace, hence for trace 1001, 2001 etc. This is because GPS data could not be written to disk at the same rate as the trace creation. High frequency, high precision GPS times and positions were stored internally on the GPS, however, and ma...(64) Data collection: Instrumentation: -The wide band mono-pulse dipole radar (centre frequency of 7 MHz) that we used in this survey was built by the British Antarctic Survey and is known as 'DELORES'. -We processed the radar data in Reflex-Win Version 10.1. -The clutter model was written in python and is described and archived here:Recinos, B., Goldberg, D. N., Boyle, D., & Pritchard, H. (2025). bearecinos/radar-declutter: First radar-declutter release (v1.0.0). Zenodo. https://doi.org/10.5281/zenodo.15488954 Data quality: With the combination of our 3 kHz radar pulse repetition frequency, the average flying speed while surveying of ~10 m s-1 (36 km h-1) and the trace stacking and horizontal interpolation of our data processing, the horizontal sampling in our ice thickness survey averages 1.15 m (max 3.0 m, SD 0.27 m) along flightlines. However, the horizontal resolution of the bed target is limited by the Fresnel zone (effective radar footprint) of our transmitted pulses. At a frequency of 7 MHz and with the typical range of the glacier bed from the radar (~100-600 m, mean of ~160 m), the Fresnel zone has a radius of approximately 30-80 m (mean ~40 m). In the vertical, the range resolution of the picked surface and bed is nominally a quarter wavelength (~7 m), but the 'optimal vertical resolution' (the resolvable range to a single discrete, prominent reflector (King 2020)) is ~1 m, and the 'practical vertical precision' for such horizons is ~2 m at this frequency (Pritchard, King et al. 2020). This implies that the practical vertical precision in thickness is the combination in quadrature of these two precisions, i.e., ~2.8 m. The absolute accuracy of the thickness is subject to the accuracy of our assumed radar velocity in ice (0.168m/ns) with which we convert two-way radar travel times to ice thicknesses, and this is somewhat dependent on the unknown and potentially variable depth-averaged glacier water content. A range of velocities from 0.165 to 0.172 m/ns has, for example, been employed for temperate and cold ice above and below the equilibrium line of an alpine glacier (Macheret, Moskalevsky et al. 1993). This range of velocities implies a difference in ice thickness of approximately +/-2% for our survey (equivalent to a change in mean thickness from 139 m when using a velocity of 0.168 m ns-1 to between 137 m and 142 m for the reasonable range of velocities). Given the dependence on water content, this could be manifest as a thickness bias that varies broadly with altitude, with our results potentially too thick by up to 2% at lower (warmer) altitudes, too thin by up to 2% at higher (colder) altitudes. Potentially more significant bias (e.g., tens of metres) could result from mistaking a non-bed reflection horizon for the bed, which we sought to avoid with our clutter modelling. To assess the consistency of our picked thickness measurements, we quantified the difference in thickness at 79 flightline crossovers. The mean absolute crossover difference was 9 m and the mean relative difference was 7% of thickness (median 6 m and 5%) (Table 1). We also compared our airborne survey results to previous ground-based radar surveys on Khumbu (Gades, Conway et al. 2000) and Ngozumpa glaciers (Pritchard, King et al. 2020). On Khumbu Glacier, seven radar cross profiles were surveyed in 1999 over the glacier tongue below the Khumbu Icefall, totalling 3.3 km in length (Gades, Conway et al. 2000). Of these, two lines crossed within ~200 m horizontally of two of our successfully surveyed cross profiles. While the earlier ground-based survey achieved profile lengths of ~500 m each, spanning most of the glacier width, we were only able to pick the bed over around 70 m of our profiles at each location. Although these surveys differ in date, method and exact location, the thicknesses reported by both surveys are similar: we measured maximum thicknesses of 445 m close to line P and 440 m close to line BC, compared to maxima of ~370 +/- 20 m (line P) and 440 +/- 20 m (line BC) in the previous study (Pritchard, King et al. 2020). A thickness of inferior or egual to 450 +/- 70 m close to these lines was also observed by a terrestrial gravity survey in 1976 (Moribayashi 1978). ____________________________________________ Crossover summary | Mean | SD | Median | Max | ____________________________________________ Relative difference (%) | 7% | 7% | 5% | 30% | _...(30) asNeeded completed