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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 2022/23 (CXA1) 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 SAD corridor (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 Untargeted transit lines 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). 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 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. 

Geophysical Investigations of Marie Byrd Land Lithospheric Evolution (GIMBLE) The PIs propose to use airborne geophysics to provide detailed geophysical mapping over the Marie Byrd Land dome of West Antarctica. They will use a Basler equipped with advanced ice penetrating radar, a magnetometer, an airborne gravimeter and laser altimeter. They will test models of Marie Byrd Land lithospheric evolution in three ways: 1) constrain bedrock topography and crustal structure of central Marie Byrd Land for the first time; 2) map subglacial geomorphology of Marie Byrd Land to constrain landscape evolution; and 3) map the distribution of subglacial volcanic centers and identify active sources. Marie Byrd Land is one of the few parts of West Antarctica whose bedrock lies above sea level; as such, it has a key role to play in the formation and decay of the West Antarctic Ice Sheet (WAIS), and thus on eustatic sea level change during the Neogene. Several lines of evidence suggest that the topography of Marie Byrd Land has changed over the course of the Cenozoic, with significant implications for the origin and evolution of the ice sheet. Two seasons were flown. ICP5 operated from Byrd Camp using Basler C-GJKB and the HiCARS2 radar in January 2013, and ICP6 operated from WAIS Divide Camp using Basler C-FMKB and the MARFA radar in late 2014, both supported by the US Antarctic Program and Kenn Borek Air. ICP6 experienced issues with data overflow on the MARFA system, with resulted in missing radar records and timing ambiguities. GIMBLE data can be found at https://www.usap-dc.org/view/project/p0000435. 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: MBL corridor (MBL/MKB##/X|Y###) rotated from the EPSG:3031 polar stereographic projection at 61.75 degrees and separated by 7.5 km in the Y direction and 5 km in the X direction, with an origin of X -579.6 km and Y -803.3 km Untargeted transit lines used the name of the expedition (ICP5|ICP6) as the project, and used the flight and the increment within the flight to name the Transect (eg (ICP6/MKB2l/F19T01a). Processing These data represent focused VHF radargrams. The data are from the HiCARS2/MARFA radar system, a 60 MHz ice penetrating radar system that has operated in several different guises over the years. HiCARS2/MARFA operates with a 1 microsecond chirp with a design bandwidth of 15 MHz, allowing for ~8 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, for MARFA the antennas are recorded separately. In ground processing, the data was processed using focusing SAR over a range delay of 100 nsec following Peters et al, 2007 (doi:10.1109/TGRS.2007.897416). Where data loss in ICP6 prevented the generating of focused data, simpler unfocused 'pik1' data was substituted, with 10 coherent stakes and 5 incoherent stacks. 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 field work was supported by NSF grant 1043761 to Young; ICP5 aircraft lease costs were supported by NASA Operation Ice Bridge grant NNX11AD33G. Data processing costs were supported by a gift from the G. Unger Vetlesen Foundation and the Open Polar Radar project (NSF grant 2127606)