Abstract:
These two files (.csv) provide independent methods of quantifying subglacial roughness in Greenland, both calculated from radio-echo sounding (or ice penetrating radar) data collected by the Operation Ice Bridge programme using CReSIS instrumentation. They are an output of the Basal Properties of Greenland (BPOG) project (http://bpog.blogs.ilrt.org/), with funding from NERC grant NE/M000869/1.
Roughness here, and in the wider literature, is defined as the variation in bed elevation (in the vertical) at the ice-bed interface, over a given length-scale. These two metrics calculate/quantify this variation in different ways: one shows topographic-scale roughness, calculated from the variation in along-track topography (bed elevation measurements derived from the radar pulse); and the other shows scattering-derived roughness, calculated from quantifying characteristics of each bed-echo (the return from the radar pulse at the ice-bed interface).
Keywords:
Geophysics, Ice penetrating radar, Radio-echo sounding, Scattering, Subglacial roughness, Topography
Cooper, M., & Jordan, T. (2018). Subglacial bed roughness of Greenland, provided using two independent metrics (Version None) [Data set]. Polar Data Centre, Natural Environment Research Council, UK. https://doi.org/10.5285/6071926f-32e0-4681-a50d-aab08f42c08a
| Access Constraints: | No restrictions apply. |
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| Use Constraints: | This data is governed by the NERC data policy http://www.nerc.ac.uk/research/sites/data/policy/ and supplied under Open Government Licence v.3 http://www.nationalarchives.gov.uk/doc/open-government-licence/version/3/. |
| Creation Date: | 2018-02-02 |
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| Dataset Progress: | Complete |
| Dataset Language: | English |
| ISO Topic Categories: |
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| Parameters: |
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| Personnel: | |
| Name | UK PDC |
| Role(s) | Metadata Author |
| Organisation | British Antarctic Survey |
| Name | Dr Tom M Jordan |
| Role(s) | Investigator |
| Organisation | Univeristy of Bristol |
| Name | Prof Martin Siegert |
| Role(s) | Investigator |
| Organisation | Imperial College London |
| Name | Dr Chris Williams |
| Role(s) | Investigator |
| Organisation | University of Bristol |
| Name | Prof Jonathan Bamber |
| Role(s) | Investigator |
| Organisation | University of Bristol |
| Name | Mr Michael Cooper |
| Role(s) | Investigator, Technical Contact |
| Organisation | University of Bristol |
| Name | Prof Dustin Schroeder |
| Role(s) | Investigator |
| Organisation | Stanford University |
| Parent Dataset: | N/A |
| Reference: | A more complete methodology and commentary about these Greenland subglacial roughness datasets will be available in Cooper et al (in prep.) Joughin I, Smith B, Howat I, Scambos T and Moon T (2016b) MEaSUREs multi-year Greenland Ice sheet velocity mosaic, version 1. NASA National Snow and Ice Data Center Distributed Active Archive Center, Boulder, Colorado, USA. (doi: 10.5067/QUA5Q9SVMSJG) |
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| Quality: | Quality control was taken from the original data source; only 'csv_good' files were used, and where appropriate 'high quality' picks, as per the CReSIS radar depth sounder documentation (see ftp://data.cresis.ku.edu/data/rds/rds_readme.pdf). 'csv_good' files only contain data points where the ice surface and ice bottom were detected. Both datasets are point data. For TopoR_icemask.csv, each point is the mid-point of a 200 m 'bin'. |
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| Lineage: | The first file, TopoR_icemask.csv, shows topographic-scale roughness, calculated from the variation in along-track topography (bed elevation measurements derived from the radar pulse) at a 200 m length-scale (the bin size used). This dataset presents the spatial pattern of roughness beneath the ice, clipped to ice mask, and filtered with respect to direction of flow. As this data is filtered with respect to flow, it allows for study of anisotropy in roughness (with regards to surface flow direction). TopoR_icemask.csv includes data from all seasons from 1993 - 2016 campaigns. This dataset is derived using a moving 'bin' to calculate root mean square (rms) height for CReSIS along-track topography data (L2 RDS data). The flow filtering is done using Joughin et al (2016b) ice surface velocity mosaic. The second file, ScatR_icemask.csv, shows scattering-derived roughness, calculated from quantifying characteristics of each bed-echo (the return from the radar pulse at the ice-bed interface). A roughness 'value' (expressed in 'metres') is inverted from the 'abruptness' (or pulse peakiness) of the bed return using a scattering model. Theoretically, this dataset presents the spatial pattern of roughness sensitive to roughness between the scale of the wavelength (order meter) and the Fresnel zone (order hundred meters) beneath the ice, clipped to ice mask. The 'scattering derived' roughness provides a more fine-scale roughness value (i.e. presents more information about roughness at scales less that 200 m). ScatR_icemask.csv includes data from CReSIS seasons: 2011-2014 P3; 2011 TO, 2009 TO, 2008 TO, 2006 TO, 2005 TO, 2010 DC8. This dataset is calculated from bed-echo characteristics, using a scattering model, to invert rms height (scattering-derived roughness) from waveform abruptness; this is calculated using the CReSIS data (L1 RDS). For the complete methodology, please see Cooper et al. (in prep.) |
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| Temporal Coverage: | |
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| Start Date | 1993-01-01 |
| End Date | 2016-12-31 |
| Spatial Coverage: | |
| Latitude | |
| Southernmost | 60 |
| Northernmost | 90 |
| Longitude | |
| Westernmost | -80 |
| Easternmost | 10 |
| Altitude | |
| Min Altitude | N/A |
| Max Altitude | N/A |
| Depth | |
| Min Depth | N/A |
| Max Depth | N/A |
| Data Resolution: | |
| Latitude Resolution | N/A |
| Longitude Resolution | N/A |
| Horizontal Resolution Range | 100 meters - < 250 meters |
| Vertical Resolution | N/A |
| Vertical Resolution Range | N/A |
| Temporal Resolution | N/A |
| Temporal Resolution Range | N/A |
| Location: | |
| Location | Arctic |
| Detailed Location | Greenland |
| Data Collection: | Data was collected with a Multichannel Coherent Radar Depth Sounder (MCoRDS) developed by the Center for Remote Sensing of Ice Sheets (CReSIS). |
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| Distribution: | |
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| Distribution Media | Online FTP |
| Distribution Size | 1.5 GB |
| Distribution Format | ASCII |
| Fees | N/A |
| Data Storage: | Both datasets are in CSV and are provided with the same structure: TopoR_icemask.csv Columns headers: Lon, Lat, X, Y, TopoR, AlongF X, Y, are projected into EPSG:3413, NSIDC TopoR is the root mean square (rms) height value (in metres) AlongF is a marker for alignment with ice surface flow direction - 0, not aligned; 1, aligned perpendicular to flow; 2, aligned parallel to flow ScatR_icemask.csv Columns headers: Lon, Lat, X, Y, ScatR, PeakI X, Y, are projected into EPSG:3413, NSIDC ScatR is the inverted rms height value of scattering-derived roughness (in metres) PeakI is a near-radar-system-independent value of pulse peakiness/abruptness for CReSIS instrumentation |