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These laser altimetry data were collected as part of the 2023-24 <a href="https://www.coldex.org">NSF COLDEX </a> CXA2 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 Missing values have been replaced by "nan".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 6.8 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: 0.340 degrees; pitch: -0.505 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. 

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)