DOI: 10.5285/776612d1-573c-49c4-aff5-23b0fba48271
title: Processed line aeromagnetic data over the Thwaites glacier region (2018/19 season)

description: Aeromagnetic data provides important constraints on the sub-surface geology of a region. This dataset contains aeromagnetic line data collected by the British Antarctic Survey as part of the International Thwaites Glacier Collaboration (ITGC). Data were collected using a caesium magnetometer system, and have been corrected to total field values following the approach laid out by the SCAR ADMAP working group (http://admap.kopri.re.kr/ADMAP-2_SCR_27Aug13.pdf). Across flow flights were generally flown at a constant altitude ~450 m above the ice surface, but data was also collected along draped sections flown along the ice flow direction. In total 9872 km of data is presented, of this 6033 km was collected in the main survey area, while other data was collected on input transit flights. The aircraft used was the BAS aerogeophysicaly equipped twin otter VP-FBL. Data are available in ASCII file format (.xyz).
description: PROCESSING: Raw line aeromagnetic data from the 2018/19 ITGC airborne survey were initially corrected for the regional geomagnetic field (IGRF), and compensated for aircraft motion. Compensation coefficients were calculated from a calibration flight flown ~500m above the Lower Thwaites Glacier field camp during the survey. Diurnal variations in the magnetic field were recorded at 30 second intervals using two base stations, one at the Lower Thwaites Glacier field camp, and a second temporary station at the Beamish Drill camp on the Rutford Ice Stream. Base station corrections were calculated by subtracting the local mean base station value across the survey from the recorded base station values. The base station corrections were then filtered with a 30 minute filter to ensure short wavelength signals, likely only seen at the base station, were not transferred to the airborne dataset. The Beamish base station was used to correct the initial input flight and the Lower Thwaites Glacier base station was used to correct all the flights in the main survey area. No base correction was applied to the other transits. An additional Tip Tank correction was made to remove the offsets induced by aircraft operational procedures such as pumping fuel. The tip correction was calculated assuming a linear trend between the DC offset at the start and end of each tip-tank event. This correction is generally restricted to turns and transits, as data quality is worse during these times, and users may wish to consider discarding this data. All the processing has been carried out using Geosoft Oasis Montaj software package. RESOLUTION: The line spacing for the survey is variable between 5 km and 10 km. Line data is generally designed to interleave with existing AGASEA data. The provided data is sampled at 10Hz, which equates to a 6m along track sample spacing. A ~1Hz sinusoidal signal is recognised in the data, and application of 3 second (18 m) low pass filter is therefore recommended. The true usable resolution of this dataset is proportional to the depth to source, which is typically 750 to 1500 m. DATA FORMAT: Data are provided in ASCII file format (.xyz). The aeromagnetic data set includes the following channels: Flight: Sequential survey flight number from T03 to T14. Date: Date YYYY/MM/DD Time_GPS: Time (GPS) HH:MM:SS.SSSSS Lon_deg: Longitude DDD.DDDDDDDD Lat_deg: Latitude DD.DDDDDDDD X: coordinate m Polar stereographic true scale -71 Y: coordinate m Polar stereographic true scale -71 Hght_GRS80: Elevation on the GRS80 ellipsoid RMag: Raw total field magnetic data (nT) XFg_Step: X fluxgate Yfg_Step: Y fluxgate Zfg_step: Z fluxgate MagC: Compensated total field magnetic data (nT) IGRF: IGRF correction (nT) MagRTC: Mag after IGRF, compensation and tip correction (nT) Tcor: Tip correction (nT) Bcor: Base station correction with 30 minute mean filter (nT) MagBRTC: Mag after all corrections (nT) Km: Projected along-track distance (km)
description: Data was collected using the BAS aerogeophysicaly equipped twin otter VP-FBL. Magnetic data was collected using wing tip mounted Scintrex CS-3 High Sensitivity Cs magnetometers. Only data from the magnetometer with the lowest noise characteristics is reported here. Data was recorded at 10 Hz on a PicoEnvirotec logging system. Additional base station information from proton procession magnetometers set up as base stations and recording 1 sample every 30 seconds was used during data processing.
description: After the basic processing presented here the standard deviation of the crossover errors within the ITGC survey was 16.3 nT.