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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). 

This is a pointer to the Open Polar Radar website and flight based CReSIS SAR processed data. 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. Raw 3 TB data from both seasons 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. 2022-23 (CXA1) flight based HDF5/matlab format data is available here: https://data.cresis.ku.edu/data/rds/2022_Antarctica_BaslerMKB/ 2023-24 (CXA2) flight based data HDF5/matlab format is available here: https://data.cresis.ku.edu/data/rds/2023_Antarctica_BaslerMKB/ 2022-23 (CXA1) transect based (science organized) unfocused data in netCDF format is available here: https://doi.org/10.18738/T8/XPMLCC 2023-24 (CXA2) transect based (science organized) unfocused data in netCDF format is available here: https://doi.org/10.18738/T8/FV6VNT Reprojected transect based images (science organized) in standard image (png, jpg) formats will be available here: ttps://doi.org/10.18738/T8/NEF2XM 

Abstract. Ice shelves play a critical role in the long-termstability of ice sheets through their buttressing effect. The underlyingbathymetry and cavity thickness are key inputs for modelling future icesheet evolution. However, direct observation of sub-ice-shelf bathymetry istime-consuming, logistically risky, and in some areas simply not possible.Here we use new compilations of airborne and marine gravity, radar depthsounding, and swath bathymetry to provide new estimates of sub-ice-shelfbathymetry outboard of the rapidly changing West Antarctic Thwaites Glacierand beneath the adjacent Dotson and Crosson ice shelves. This region is ofspecial interest, as the low-lying inland reverse slope of the ThwaitesGlacier system makes it vulnerable to marine ice sheet instability, withrapid grounding line retreat observed since 1993 suggesting this process maybe underway. Our results confirm a major marine channel >800 mdeep extends tens of kilometres to the front of Thwaites Glacier, while theadjacent ice shelves are underlain by more complex bathymetry. Comparison ofour new bathymetry with ice shelf draft reveals that ice shelves formedsince 1993 comprise a distinct population where the draft conforms closelyto the underlying bathymetry, unlike the older ice shelves, which show a moreuniform depth of the ice base. This indicates that despite rapid basalmelting in some areas, these recently floated parts of the ice shelf are notyet in dynamic equilibrium with their retreated grounding line positions andthe underlying ocean system, a factor which must be included in futuremodels of this region's evolution. 

ABSTRACT The catchments of Pine Island Glacier and Thwaites Glacier in the Amundsen Sea Embayment are two of the largest, most rapidly changing, and potentially unstable sectors of the West Antarctic Ice Sheet. They are also neighboring outlets, separated by the topographically unconfined eastern shear margin of Thwaites Glacier and the southwest tributary of Pine Island Glacier. This tributary begins just downstream of the eastern shear margin and flows into the Pine Island ice shelf. As a result, it is a potential locus of interaction between the two glaciers and could result in cross-catchment feedback during the retreat of either. Here, we analyze relative basal reflectivity profiles from three radar sounding survey lines collected using the UTIG HiCARS radar system in 2004 and CReSIS MCoRDS radar system in 2012 and 2014 to investigate the extent and character of ocean access beneath the southwest tributary. These profiles provide evidence of ocean access ~12 km inland of the 1992–2011 InSAR-derived grounding line by 2014, suggesting either retreat since 2011 or the intrusion of ocean water kilometers inland of the grounding line.