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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. 

<p><b> Introduction </b> <br> The National Science Foundations Center for Oldest Ice Exploration (<a href="https://www.coldex.org">NSF COLDEX</a>) is a Science and Technology Center working to extend the record of atmospheric gases, temperature and ice sheet history to greater than 1 million years. As part of this effort, NSF COLDEX has been searching for a site for a continuous ice core extending through the mid-Pleistocene transition. Two seasons of airborne survey were conducted from South Pole Station across the southern flank of Dome A. </p> <p><b> 2023-2024 Field Season </b> <br> In the 2023-2024 field season (CXA2), and using a BT-67 Basler, NSF COLDEX conducted 17 flights from South Pole Station toward the southern flank of Dome C. Three test flights were conducted from McMurdo Station. Instrumentation included the <a href="https://doi.org/10.18738/T8/J38CO5">60 MHz MARFA ice penetrating radar </a> from the University of Texas Institute for Geophysics, a <a href="https://doi.org/10.1109/IGARSS53475.2024.10640448">UHF ice penetrating radar </a> from the Center for Remote Sensing and Integrated Systems; an GT-2 Gravimeter, and LD-90 laser altimeter and an G-823 Magnetometer. </p> <p><b> Basal specularity content </b> <br> These basal specularity content were derived from comparing 1D and 2D focused MARFA data (<a href="http://doi.org/10.1109/TGRS.2007.897416">Peters et al., 2007</a>). By comparing bed echo strengths for different focusing apertures, and accounting for the ranges and angles involved, we can derive the "specularity content" of the bed echo, a proxy for small scale bed roughness and a good indicator for subglacial water pressure in regions of distributed subglacial water (<a href="https://doi.org/10.1109/LGRS.2014.2337878">Schroeder et al., 2014, IEEE GRSL </a>, <a href="https://doi.org/10.1016/j.epsl.2019.115961">Dow et al., 2019, EPSL </a>) and smooth deforming bed material (<a href="http://doi.org/10.1002/2014GL061645">Schroeder et al., 2014, GRL</a>, <a href="http://dx.doi/org/10.1098/rsta.2014.0297">Young et al., 2016, PTRS</a>. Specularity data are inherently noisy, so these products have been smoothed with a 1 km filter.</p> 

<p><b> Introduction </b> <br> The National Science Foundations Center for Oldest Ice Exploration (<a href="https://www.coldex.org">NSF COLDEX</a>) is a Science and Technology Center working to extend the record of atmospheric gases, temperature and ice sheet history to greater than 1 million years. As part of this effort, NSF COLDEX has been searching for a site for a continuous ice core extending through the mid-Pleistocene transition. Two seasons of airborne survey were conducted from South Pole Station across the southern flank of Dome A. </p> <p><b> 2022-2023 Field Season </b> <br> In the 2022-20223 field season (CXA1), and using a BT-67 Basler, NSF COLDEX conducted 13 full flights and one weather abort from South Pole Station toward the southern flank of Dome C; as well as 1 survey flight toward Hercules Dome in support of the Hercules Dome Drilling project. Three test flights were conducted from McMurdo Station. Instrumentation included the <a href="https://doi.org/10.18738/T8/J38CO5">60 MHz MARFA ice penetrating radar </a> from the University of Texas Institute for Geophysics, a <a href="https://doi.org/10.1109/IGARSS53475.2024.10640448">UHF ice penetrating radar </a> from the Center for Remote Sensing and Integrated Systems; an GT-2 Gravimeter, and LD-90 laser altimeter and an G-823 Magnetometer. </p> <p><b> Basal specularity content </b> <br> These basal specularity content were derived from comparing 1D and 2D focused MARFA data (<a href="http://doi.org/10.1109/TGRS.2007.897416">Peters et al., 2007</a>). By comparing bed echo strengths for different focusing apertures, and accounting for the ranges and angles involved, we can derive the "specularity content" of the bed echo, a proxy for small scale bed roughness and a good indicator for subglacial water pressure in regions of distributed subglacial water (<a href="https://doi.org/10.1109/LGRS.2014.2337878">Schroeder et al., 2014, IEEE GRSL </a>, <a href="https://doi.org/10.1016/j.epsl.2019.115961">Dow et al., 2019, EPSL </a>) and smooth deforming bed material (<a href="http://doi.org/10.1002/2014GL061645">Schroeder et al., 2014, GRL</a>, <a href="http://dx.doi/org/10.1098/rsta.2014.0297">Young et al., 2016, PTRS</a>. Specularity data are inherently noisy, so these products have been smoothed with a 1 km filter.</p> 

{"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> 

ESCHER (Exploration of Saline Cryospheric Habitats with Europa Relevance) is a NASA funded PSTAR (Planetary Science and Technology from Analog Research) program with the general geophysical goals of characterizing the subglacial environment of Devon Ice Cap in Nunavut, Canada as a potential planetary analog. The project seeks to gather additional evidence for unique chemistry in the subglacial hydrological system and to further the technical development of the scientific instrumentation. ESCHER represents the first field deployment of a multi-polarization radar system on an A-Star 350 B2 helicopter platform. This is the sixth polar deployment of this helicopter geophysical system, and the first in the arctic. The previous helicopter-based systems expeditions were KRT1, KRT2, ASE2, ASE3, ASE4. Similar results for ASE3 are described in Pierce et al, 2023, and Pierce et al, 2024. The science goals include characterizing the subglacial environment from the summit of Devon Ice Cap to Sverdrup Glacier’s marine termination. The study area includes three linked geographical regions: i) The summit area where Rutishauser et al. (2020), presented further evidence for the existence of fluid at the base of Devon Ice Cap; ii) the shoulder region of the ice cap, just upstream of the ice flow that enters the outlet valleys of Fox and Sverdrup Glaciers. This region includes the hypothesized distributed hydrological system that transitions into channelized geometry, and iii) The Sverdrup/Fox valley glaciers, tidewater terminus, and locations of subglacial discharge. The study region also includes the upper catchment of the Crocker Bay Glaciers and some of the western land terminating flanks of the ice cap. All data in this collection is derived from a multipolarization version of the Helicopter Radar (HERA) system (Lindzey et al., 2017, 2022). Included in this dataset are the Level 2 time registered geophysical observables for the specific lines mentioned in Pierce et al., (2024); ice thickness, partial bed reflectivity, surface reflectivity, bed and surface elevation derived both from incoherent processing (IR2HI2) and focused processing (IRFOC2; Peters et al., 2007); no multipolarization processing is included here. Also included is specularity content (IRSPC2; Schroeder et al., 2014, Young et al, 2016). Data consists of ASCII tab delimited tables, with header describing the columns and key metadata on a per transect basis. Images showing simple maps of values are also included. The following transects are included: DEV3/PER0a/Y79a DEV3/PER0a/Y80a DEV3/PER0a/Y81a DEV3/PER0a/Y82a DEV3/PER0a/Y83a DEV3/PER0a/Y84a DEV3/PER0a/Y85a DEV3/PER0a/Y86a DEV3/PER0a/Y87a References: Pierce, C., 2024, Advanced Analysis of the Sub-Glacial Environment Using Radar Echo Sounding Simulations, Ph. D. Thesis, Montana State University Pierce, C., Gerekos, C., Skidmore, M., Beem, L., Blankenship, D., Lee, W. S., Adams, E., Lee, C.-K., and Stutz, J., 2024, Characterizing sub-glacial hydrology using radar simulations, The Cryosphere, 18, 4, 1495--1515, 10.5194/tc-18-1495-2024 Pierce, C., Skidmore, M., Beem, L., Blankenship, D., Adams, E., and Gerekos, C., 2024, Exploring canyons beneath Devon Ice Cap for sub-glacial drainage using radar and thermodynamic modeling, Journal Of Glaciology, 1--18, 10.1017/jog.2024.49 Lindzey, L., Quartini, E., Buhl, D., Blankenship, D., Richter, T., Greenbaum, J., and Young, D., 2017, KRT1/LGV1 Season Field Report, 237 10.26153/tsw/11620 Lindzey, L. E., Beem, L. H., Young, D. A., Quartini, E., Blankenship, D. D., Lee, C.-K., Lee, W. S., Lee, J. I., and Lee, J., 2020, Aerogeophysical characterization of an active subglacial lake system in the David Glacier catchment, Antarctica, The Cryosphere, 14, 7, 2217--2233, 10.5194/tc-14-2217-2020 Peters, M. E., Blankenship, D. D., Carter, S. P., Young, D. A., Kempf, S. D., and Holt, J. W., 2007, Along-track Focusing of Airborne Radar Sounding Data From West Antarctica for Improving Basal Reflection Analysis and Layer Detection, IEEE Transactions On Geoscience And Remote Sensing, 45, 9, 2725-2736, 10.1109/TGRS.2007.897416Rutishauser, A., Blankenship, D. D., Young, D. A., Wolfenbarger, N. S., Beem, L. H., Skidmore, M. L., Dubnick, A., and Criscitiello, A. S., 2022, Radar sounding survey over Devon Ice Cap indicates the potential for a diverse hypersaline subglacial hydrological environment, The Cryosphere, 16, 379-395, https://doi.org/10.5194/tc-16-379-2022 Schroeder, D. M., Blankenship, D. D., Raney, R. K., and Grima, C., 2015, Estimating subglacial water geometry using radar bed echo specularity: application to Thwaites Glacier, West Antarctica, IEEE Geoscience And Remote Sensing Letters, 12, 3, 443-447, 10.1109/LGRS.2014.2337878 Young, D. A., Schroeder, D. M., Blankenship, D. D., Kempf, S. D., and Quartini, E., 2016, The distribution of basal water between Antarctic subglacial lakes from radar sounding, Philosophical Transactions Of The Royal Society A, 374, 20140297, 1-21, 10.1098/rsta.2014.0297 

These transect organized radargrams were collected as part of the Center for Oldest Ice Exploration (COLDEX) Science and Technology Center (https://www.coldex.org) in the 2023/24 (CXA2) airborne reconnaissance field season. The raw 3 TB data is deposited at the USAP data center at https://doi.org/10.15784/601768. Flight organized data with additional processing by the University of Kansas to remove electromagnetic interference can be found at the Open Polar Radar server (https://www.openpolarradar.org). 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. Dataset organization 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. Transects were collected in preplanned systems with the following parameters: CLX radials (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. CLX corridor (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 CLX2 corridor (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 NPXE radials (NPXE/MKB##/R####) primarily designed to survey the Upper Byrd Glacier Catchment, constitute spokes radiating from South Pole separated by 2 degrees, in the EPSG:3031 polar stereographic projection Untargeted transit lines used the name of the expedition (CXA2) as the project, and used the flight and the increment within the flight to name the Transect (eg (CXA2/MKB2n/F10T02a). Processing These data represent range compressed VHF radargrams as collected and analyzed in the field. The data are from the MARFA radar system, a 60 MHz ice penetrating radar system that has operated in several different guises over the years. MARFA operates with a 1 microsecond chirp with a design bandwidth of 15 MHz, allowing for ~8 meter range resolution. The record rate after onboard stacking is 200 Hz. High and low gain channels are collected from antennas on each side of the aircraft. In ground processing, the data were stacked 10x coherently to reduce range delayed incoherent surface scattering, and then stacked 5 times incoherently to improve image quality. In this preliminary processing, the effective resolution of deep scattering is several hundred meters due to range ambiguities at depth. Data format These data collection represents georeferenced, time registered instrument measurements (L1B data) converted to SI units. The data format are netCDF3 files, following the formats used for NASA/AAD/UTIG's ICECAP/OIB project at NASA's NSIDC DAAC (10.5067/0I7PFBVQOGO5). Metadata fields can be accessed using the open source ncdump tool, or c, python or matlab modules. A Keyhole Metadata Language (KML) file with geolocation for all transects is also provided. See https://www.loc.gov/preservation/digital/formats/fdd/fdd000330.shtml for resources on NetCDF-3, and https://nsidc.org/data/IR2HI1B/versions/1 for a description of the similar OIB dataset. Acknowledgements 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. 

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.