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Code for processing data and plotting figures for the paper "Dome A basal ice truncated at an extensive geologic dichotomy in the South Pole Basin of East Antarctica". 

{"Abstract":["This code generates figures for a paper titled "Coupled ice sheet structure and bedrock geology in the deep interior of East Antarctica: Results from Dome A and the South Pole Basin" submitted to Geophysical Research Letters. All four figures in the main text are generated, along with one of the supplementary figures. The code has been updated from v0.6 to account for reviewer comments."]} 

This dataset contains the basal ice unit thickness as measured by the NSF COLDEX MARFA ice-penetrating radar survey, which mainly focuses on the southern flank of Dome A. The "basal ice unit" is hereby defined as the bottom portion of the ice sheet where no clear and traceable englacial reflection is detected by the radar sounder. Raw radar data can be found at: https://doi.org/10.15784/601768. The basal ice unit is mapped using the DecisionSpace Geosciences 10ep software package. This dataset provides three data products: • Thickness of the basal ice unit • Thickness of the stratigraphic ice unit above the basal ice unit • The shape of the basal ice unit boundary, where rapid basal ice unit thinning is observed in the middle of the South Pole Basin. 

{"Abstract":["The PPT survey extended from the Ross Ice Shelf, southward over the TAM along 150W between the Scott and Reedy Glaciers, and through the South Pole. Approximately 15,000 line km were flown. North-south oriented transects were flown 10 km apart and west-east tie lines were flown with a 30 km line spacing. Fifteen km long transect 'run-ins' and 'run-outs' were added to each line, thus ensuring data collection to survey boundaries. Laser altimetry, ice-penetrating radar, gravity and magnetic field intensity data were collected. This work was funded by NSF-OPP grant 9615832 with the project title: Collaborative Research: Contrasting Architecture and Dynamics of the Transantarctic Mountains (Pensacola-Pole Transect). Principal Investigators were D.D. Blankenship, University of Texas Institute for Geophysics, and R.E. Bell and W.R. Buck, Lamont-Doherty Earth Observatory.\n<br>\n<br>\nThis work was conducted by the Support Office for Aerogeophysical Research (SOAR) NSF facility under cooperative agreement OPP-9319379. The 1998/1999 field season <a href="http://hdl.handle.net/2152/65412"> report </a>(Holt et al 1999) describes the field work in more detail.\n<br>\n<br>\nThese data are gridded orthogonal data with a point every 850 m. Data is in a space delimited ASCII table with three columns: Longitude, Latitude and geophysical observation. Grids are smoothed using a Gaussian filter (2.125 km for gravity, magnetic field anomaly, surface elevation and 8.5 km for ice thickness) and surfaced using a bicubic spline method.\n<br>\nObservations include:\n<ol>\n<li> Bed elevation (m, WGS-84) </li> \n<li> Gravity disturbance (mGal, WGS-84) </li> \n<li> Ice Thickness (m) </li> \n<li> Laser Derived Surface Elevation (m, WGS-84) </li> \n<li> Magnetic Anomaly (nT, IGRF) </li> \n<li> Radar Derived Surface Elevation (m, WGS-84) </li> \n</ol>\nA browse image is included. \n<br><br>\n<i>Acknowledgement: </i><br>\nIn keeping with NSF Grant Policy, any publication using these data (including web documents) must contain the following acknowledgment: "This material is based on work supported by the National Science Foundation under cooperative agreement OPP-9319379." Also, any oral presentation utilizing these materials should acknowledge the support of the National Science Foundation. In addition, we request that any oral presentation, web page or publication also acknowledge SOAR and the University of Texas. A suitable citation for PPT data is:\n<br>\n<i>Davis, M.B., 2001, Subglacial Morphology and Structural Geology in the Southern Transantarctic Mountains from Airborne Geophysics, M.S. Thesis, Univ. of Texas, 133 pp.<a href="http://dx.doi.org/10.26153/tsw/2786">doi:10.26153/tsw/2786</a></i>\n<br>\nThese data represent the data that was hosted on the UTIG webpage at https://www-udc.ig.utexas.edu/external/facilities/aero/data/soar/PPT/SOAR_ppt.htm."]} 

Abstract A major subglacial lake, Lake Snow Eagle (LSE), was identified in East Antarctica by airborne geophysical surveys. LSE, contained within a subglacial canyon, likely hosts a valuable sediment record of the geological and glaciological changes of interior East Antarctica. Understanding past lake activity is crucial for interpreting this record. Here, we present the englacial radiostratigraphy in the LSE area mapped by airborne ice-penetrating radar, which reveals a localized high-amplitude variation in ice unit thickness that is estimated to be ∼12 ka old. Using an ice-flow model that simulates englacial stratigraphy, we investigate the origin of this feature and its relationship to changes in ice dynamical boundary conditions. Our results reveal that local snowfall redistribution initiated around the early Holocene is likely the primary cause, resulting from a short-wavelength (∼10 km) high-amplitude (∼20 m) ice surface slope variation caused by basal lubrication over a large subglacial lake. This finding indicates an increase in LSE water volume during the Holocene, illustrating the sensitivity in volume of a major topographically constrained subglacial lake across a single glacial cycle. This study demonstrates how englacial stratigraphy can provide valuable insight into subglacial hydrological changes before modern satellite observations, both for LSE and potentially at other locations. 

<p>NSF COLDEX performed two airborne campaigns from South Pole Station over the Southern Flank of Dome A and 2022-23 and 2023-24, searching for a potential site of a continuous ice core that could sample the mid-Pleistocene transition. Ice thickness data extracted from the MARFA radar system has allow for a new understanding of this region.</p> <p>Here we generate crustal scale maps of ice thickness, bed elevation, specularity content, subglacial RMS deviation and fractional basal ice thickness with 1 km sampling, and 10 km resolution. We include both masked and unmasked grids.</p> <p> The projection is in the SCAR standard ESPG:3031 polar stereographic projection with true scale at 71˚S.</p> <p>These geotiffs were generated using performed using GMT6.5 (<a href="https://doi.org/10.1029/2019GC008515">Wessel et al., 2019</a>) using the pygmt interface, by binning the raw data to 2.5 km cells, and using the <a href="https://github.com/sakov/nn-c"> nnbathy </a> program to apply natural neighbor interpolation to 1 km sampling. A 10 km Gaussian filter - representing typical lines spacings - was applied and then a mask was applied for all locations where the nearest data point was further than 8 km. </p> Ice thickness, bed elevation and RMS deviation @ 400 m length scale (<a href="http://dx.doi.org/10.1029/2000JE001429">roughness</a>) data includes the following datasets: <ul> <li> UTIG/CRESIS <a href="https://doi.org/10.18738/T8/J38CO5">NSF COLDEX Airborne MARFA data</a></li> <li> British Antarctic Survey <a href="https://doi.org/10.5285/0f6f5a45-d8af-4511-a264-b0b35ee34af6">AGAP-North</a></li> <li> LDEO <a href="https://doi.org/10.1594/IEDA/317765"> AGAP-South </a></li> <li> British Antarctic Survey <a href="https://doi.org/10.5270/esa-8ffoo3e">Polargap</a></li> <li> UTIG Support Office for Airborne Research <a href="https://doi.org/10.15784/601588">Pensacola-Pole Transect (PPT) </a></li> <li> NASA/CReSIS <a href="https://doi.org/10.5067/GDQ0CUCVTE2Q"> 2016 and 2018 Operation Ice Bridge </a> </li> <li> ICECAP/PRIC <a href="https://doi.org/10.15784/601437"> SPICECAP Titan Dome Survey </a> </ul> <p>Specularity content (<a href="https://doi.org/10.1109/LGRS.2014.2337878">Schroeder et al. 2014</a>) is compiled from <a href="https://doi.org/10.18738/T8/KHUT1U"> Young et al. 2025a </a> and <a href="https://doi.org/10.18738/T8/6T5JS6"> Young et al. 2025b</a>.</p> <p>Basal ice fractional thickness is complied from manual interpretation by Vega Gonzàlez, Yan and Singh. </p> <p>Code to generated these grids can be found at <a href="https://github.com/smudog/COLDEX_dichotomy_paper_2025"> at github.com </a></p> 

These transect projected radargrams were collected as part of the Center for Oldest Ice Exploration (COLDEX) Science and Technology Center (https://www.coldex.org) in the 2022/23 (CXA1) and 2023/24 (CXA2) airborne field seasons. The raw 3 TB data is deposited at the USAP data center at https://doi.org/10.15784/601768. The set of images in this archive was designed for easy, non expert, access to radargrams, organized according to survey design. <p> The science goal was to characterize the ice sheet between Antarctica's Dome A and Amundsen Scott South Pole Station, to locate sites of interest for the drilling of an ice core with ages spanning the mid-Pleistocene. The radar was deployed on Balser C-FMKB, and flown at ranges of up to 800 km from South Pole Station at velocities of 90 m/s and typical altitude above ground of 600 m. Other instruments included a UHF array system provided by the University of Kansas, a gravity meter, a magnetometer, a laser altimeter, and multiple global navigation satellite systems receivers. The radar data is used for finding ice thickness, bed character, englacial structure and surface assessment. <p> <b>Dataset organization</b> Transects are provided a P/S/T nomenclature, organized by the Project they are flying in, the acquisition System (typically named after the aircraft) and the Transect within the Project. <p> Transects were collected in preplanned systems with the following parameters (examples below): <p> <i>The CLX radials</i> (CLX/MKB##/R###), attempting to emulate flow lines from Dome A and radiating (in the EPSG:3031 polar stereographic projection) from easting 965 km northing 385 km, with a separation of 0.25 degrees. <p> <i>The CLX corridor</i> (CLX/MKB##/X###) rotated from the EPSG:3031 polar stereographic projection at -150 degrees and separated by 10 km in the Y direction and 3.75 km in the X direction <p> <i>The CLX2 corridor</i> (CLX2/MKB##/X###) rotated from the EPSG:3031 polar stereographic projection at -150 degrees and separated by 2.5 km in its Y direction and 2.5 km in its X direction <p> <i>The NPXE radials</i> (NPXE/MKB##/R###) radiating (in the EPSG:3031 polar stereographic projection) from easting 0 km and northing 0 km (ie South Pole), with a separation of 2 degrees. <p> <i>The SAD corridor</i> (SAD/MKB##/X###|Y####) designed to characterize the Saddle region near South Pole approximately perpendicular to the flow lines, rooted from the EPSG:3031 polar stereographic projection at -73.8 degrees and separated by 2.5 km in its Y direction and 2.5 km in the its X direction <p> <i>Untargeted transit lines</i> used the name of the expedition (CXA1) as the project, and used the flight and the increment within the flight to name the Transect (eg (CXA1/MKB2n/F10T02a). <p> <b>Processing</b> These images were processed using the CReSIS Synthetic Aperture Radar Processor (CSARP), as part of the Open Polar Radar Effort. Data were processed using pulse compression and matched filter approach for focusing optimized for producing data with 25 m along track sampling. Radio Frequency Interference was partially removed. See the Open Polar Radar server for more detail. <p> <b>Data format</b> Radar data is provided in three formats: <p> <i>Browse</i> data in PNG format are provided with marked axis depth projected, correcting for the velocity of ice, and projected along track into consistent project coordinates. Turns are trimmed off. Long transects are projected to ~30x vertical exaggeration, shorter transects have constant size. <p> <i>Image</i> data in grayscale JPEG format are provided without ornamentation. but are depth projected, correcting for the velocity of ice, and projected along track into consistent project coordinates. Turns are trimmed off. All images have a constant vertical scale of 1.69 m/pixel and horizontal scale of 25 m per pixel. The minimum black value corresponds to -140 dB, and the maximum white value corresponds to 0 dB, for a resolution of ~0.5 dB. Use of this data for radiometric interpretation has not been validated. <p> <i>Metadata</i> is provided in in comma delimited csv format. Columns included: <p> CSARP record (the number of record or trace in the original flight based processing<br> UNIX time [s] (seconds from midnight January 1, 1970, with no leap seconds) <br> Longitude [degrees] (WGS-84) <br> Latitude [degrees] (WGS-84) <br> Aircraft Elevation [m] (WGS-84) <br> Surface Echo Delay [s] (time delay between surface echo and transmission) <br> Roll [degrees] (right wing down positive) <br> Pitch [degrees] (nose down positive) <br> Heading [degrees] (right of North) <br> EPSG 3031 Easting [m] (projected coordinate) <br> EPSG 3031 Northing [m] (projected coordinate) <br> displayed_distance [km] (x-axis distance) <br> surface_elevation [m] (radar estimate surface elevation, WGS-84)<br> blanking [px] (sampled (blanked above surface return)<br> Elevation of image top [m] (WGS-84 elevation of the top of the projected image) <br> Elevation of image bottom [m] (WGS-84 elevation of the bottom of the projected image) <br> <p> A summary csv file is provided with transect name, start and end points in geographic and projected coordinates, and projection. <p> <b>Acknowledgements</b> This work was supported by the Center for Oldest Ice Exploration, an NSF Science and Technology Center (NSF 2019719). We thank the NSF Office of Polar Programs, the NSF Office of Integrative Activities, and Oregon State University for financial and infrastructure support, and the NSF Antarctic Infrastructure and Logistics Program, and the Antarctic Support Contractor for logistical support. Additional support was provided by the G. Unger Vetlesen Foundation and the NSF-sponsored Open Polar Radar project (NSF 2126503 & 2127606). 

These laser altimetry data were collected as part of the 2022-23 <a href="https://www.coldex.org">NSF COLDEX </a> CXA1 airborne campaign targeting the southern flank of East Antarctica's Dome A. In this Level 2 product, we have used the laser range to the surface and complementary aircraft position data to calculated the ice surface elevation, which is an important constraint on ice flow. Complementary radar, gravity, magnetics and imagery were also collected. <p> <i>Data format:</i>Data are formatted as text files with a header and the following tab delimited format columns. Data are in the same format as similar <a href="https://doi.org/10.5067/JV9DENETK13E"> IceBridge ILUTP2 altimetry data. </a> <p> Field 1: Year (UTC)<br> Field 2: Day of year (UTC)<br> Field 3: Second of day (UTC)<br> Field 4: Longitude Angle (deg) (WGS-84) <br> Field 5: Latitude Angle (deg) (WGS-84)<br> Field 6: Laser Derived Surface Elevation (m) (WGS-84)<br> <p> Missing values have been replaced by "nan". The effective footprint of the laser data is 25 m along track by 1 meter across track. Some cloud filtering was performed. <p> <i>Uncertainties</i>: A comparison of this laser altimetry dataset north of 87.5˚S with the <a href="https://doi.org/10.7910/DVN/EBW8UC"> REMAv2 </a>100 m mosaic digital terrain model indicate a median bias of 17 cm and a root mean squared (RMS) difference of 20 cm. Intersections between profiles within this survey, on the Antarctic Plateau but away from South Pole Station, have RMS differences of 6.4 cm. <p> <i>Datum: </i>WGS-84 ellipsoid; ITRF 2008 <p> <i>Geolocation: </i>Positioning and orientation for CXA1 came from loosely coupled joint PPP/inertial solutions using a Novatel OEM-4 GPS receiver and an iMAR FSAS IMU. <p> <i>Pointing bias: </i> roll: -0.2 degrees; pitch: -0.350 degrees <br> Pointing angle (pointing bias) is the angular offset of the downward-pointing laser boresight respect to the vehicle body frame's vertical (Z) axis. This estimated angle is derived by comparing measurements at crossovers. Pointing angle is provided in the vehicle body frame, using the laser origin for the rotation node. A positive pitch rotation indicates that the laser beam intersects the ground forward of the z-axis. A positive roll rotation indicates that the laser beam intersects the ground left of the z-axis. Pointing biases were found using the minimization of cross over difference method from <a href="http://dx.doi.org/10.3189/2015JoG14J048">Young et al., 2015</a>. <p> <i>Level arm: </i>X: 0 m; Y: 0.2 m; Z: -0.22 m <br> The lever arm is the position of the laser origin relative to the aircraft position solution, estimated using crossover-error minimization. Lever arm is provided in the vehicle body frame, with +X is forward, +Y is right, and +Z is down. Lever arm was measured after installation in the field. <p> <i>GNSS_antenna: </i>AeroAntenna AT1675-17W-TCNF-000-RG-36-NM <br> The coordinate system for the laser-gps lever arm is X forward, Y right, and Z down, from the center of position. 

This dataset constitutes the as-recorded echo data from the MARFA radar system. The data was recorded by a National Instruments acquisition system, simultaneously with GPS, magnetics, laser range data, outside air temperature and IMU data. The data was acquired using the Environment for Linked Serial Acquisition (ELSA). The data is provided in two forms: • Flight based and as recorded on the aircraft in raw packets • Transect based, reorganized into transects corresponding to the survey design, and demultiplexed into text tables and flat binary files.