<b>NSF COLDEX CXA1 laser ranging, magnetic field strength and orientation, and positioning</b><br><br>This data collection represents georeferenced, time registered instrument measurements (Level 1B data) converted to SI units, and is of most interest to users who wish to reprocess the data. Users interested in geophysical observables (eg magnetic anomalies and surface elevation) should used the derived Level 2 datasets. The data format are space delimited ASCII files, following the formats used for UTIG predecessor ICECAP/OIB project at NASA's NSIDC DAAC. Fields are described in the # delimited detailed header for each granule.<br><br><b>DATASET ORGANIZATION</b><br>Transects were collected in preplanned systems with the following parameters:<ul><li>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.</li><li>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.</li><li>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.</li><li>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.</li><li>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).</li></ul><br><b>POSITIONING</b><br>GPS provides the positioning (and timing) for all other data streams:<br><ul><li>IPUTG1B (ICECAP Positioning/UTIG GPS Level 1B): real time CA-code 1 Hz GPS position data</li></ul><br><b>MAGNETICS</b><br>Magnetic data provides constraints on the depth to crystalline rock, the temperature structure of the crust, and the underlying tectonics<br><ul><li>IMGEO1B (ICECAP Magnetics: Geometrics Level 1B): georeferenced total magnetic field data; 10 Hz ASCII</li><li>IMFGM1B (ICECAP Magnetics/Flux Gate Magnetometer Level 1B): georeferenced aircraft referenced magnetic field vectors; 10 Hz ASCII</li></ul><br><b>ALTIMETRY</b><br>Laser altimetry provides for surface shape and altimetry validation. See <a NSF href="https://doi.org/10.18738/T8/99IEOG"> COLDEX 2022-23 Riegl Laser Altimeter Level 2 Geolocated Surface Elevation Triplets</a> for derived surface elevation data.<br><ul><li>ILUTP1B (ICECAP Lidar/UTIG Profiler Level 1B): georeferenced laser range data, no orientation corrections; 3.5 Hz ASCII</li></ul><br>This work was supported by the U.S. National Science Foundation Center for Oldest Ice Exploration (NSF COLDEX), an NSF Science and Technology Center (NSF 2019719). We thank the NSF Office of Polar Programs, the NSF Office of Integrative Activities and the NSF Antarctic Infrastructure and Logistics Program, Kenn Borek Airlines and the Antarctic Support Contractor for logistical support. Additional support came from the Open Polar Radar project (NSF grant 2127606) award to the University of Texas at Austin and a gift to UTIG from the G. Unger Vetlesen foundation.

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.<br><br>This 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.<br><br>These 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.<br>Observations include:<ol><li> Bed elevation (m, WGS-84) </li> <li> Gravity disturbance (mGal, WGS-84) </li> <li> Ice Thickness (m) </li> <li> Laser Derived Surface Elevation (m, WGS-84) </li> <li> Magnetic Anomaly (nT, IGRF) </li> <li> Radar Derived Surface Elevation (m, WGS-84) </li> </ol>A browse image is included. <br><br><i>Acknowledgement: </i><br>In 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:<br><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><br>These 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.

<article> <header> <h2>NSF COLDEX GPS/IMU Level 1B Airborne Position and Attitude Solutions</h2> </header> <p> These data are results processed using Hexagon | NovAtel's Waypoint Inertial Explorer, a GUI environment for performing joint Inertial Measurement Unit (IMU) / Global Positioning System (GPS) kinematic position and attitude solutions. The raw data used for creating these solutions is at <a href="https://doi.org/10.15784/601933" target="_blank" rel="noopener noreferrer"> Young et al., 2025 [USAP-DC] </a>. Manual steps included cutting out bad portions of data and removing bad GPS satellite range information. Only the US GPS constellation of satellites was used. </p> <p>Two types of solution are provided.</p> <section> <em>wpt1</em> solutions are produced by jointly processed IMU rotation rate and acceleration data with GPS data using a Kalman filter to produce an internally consistent position and aircraft attitude solution at the center of the IMU unit at a rate of 50 Hz. Loosely coupled solutions first perform kinematic precise point positioning (PPP) solving the GPS range data for 1 Hz positions, and then fit the IMU data to interpolate positions and find attitude. Tightly coupled solutions incorporate the IMU data into the position solutions. Accuracies are typically on the order of a few cm. </p> </section> <section> <em>wpt2</em> solutions only have the PPP position solution, and provide redundancy in the case of an IMU issue. These produce data at the rate of the GNSS receiver (typically 1–2 Hz). </p> </section> <section> <p>Files have the following name convention:</p><code>SEASON_PLATFORM_FLIGHT_PROCESSING.wpt#</code> <p> Here the <code>SEASON</code> is either <em>CXA1</em> (the 2022–23 NSF COLDEX airborne season) or <em>CXA2</em> (the 2023–24 NSF COLDEX airborne season); the <code>PLATFORM</code> is the GNSS antenna/receiver combination; the <code>FLIGHT</code> is the flight number within the season; and the <em>PROCESSING</em> is either <em>LCPPP</em> (loosely coupled with PPP), <em>TCPPP</em> (tightly coupled with PPP), or <em>PPP</em> (PPP only). Some flights have multiple files due to system restarts; other files span multiple flights due to short turn around between flights. </p> </section> <section>A file called POS_timelimits.csv contains the start and end time of each file in seconds with respect to the UNIX epoch. </section> <section> The files are in the form of tables with headers and footers delimited with the <code>#</code> character. Column names are internally defined. </p> </section></article>

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