DOI: 10.5285/4bcc9b4e-fab5-46cd-aac3-56c28e61cff1
title: Processed aeromagnetic line data flown from Rothera station with a Windracers Ultra UAV (2023/24 season)

description: Airborne magnetic data provides insight into the subsurface geology and tectonic history. This dataset includes processed airborne magnetic data collected over Marguerite Bay during the 2023/2024 Antarctic field season. This survey was carried out as part of a wider UKRI Innovate UK Future Flight-3 SWARM project in collaboration with Windracers Ltd to demonstrate their Ultra Uncrewed Aerial Vehicle (UAV) as a platform for environmental science. As part of this project ~1600 km of new high resolution aeromagnetic data with a ground clearance of 500m was collected around Rothera research station, West Antarctica. Data were acquired using a GEMSys GSMP-35U UAV magnetometer mounted on a Windracers Ultra UAV. Magnetic line data is provided as comma separated ASCII file.

This study was funded by Innovate UK through their Future flight challenge support for the "Protecting environments with unmanned aerial vehicle swarms" project (reference: 10023377). We thank BAS operations for their support and specifically the BAS air unit and ground support staff whose close cooperation and engagement with the UAV deployment made the project successful. We also thank staff at Windracers and Distributed avionics who provided remote support for UAV operations across the field season.
description: The magnetic sensor was mounted in the payload bay door of the Ultra, meaning the sensor sat ~1.5 m behind the payload bay when the door was closed. This location was chosen as other areas far from the core electronic systems and engines, such as wing tips and tail, housed electronically activated control surfaces, which would likely generate unacceptable levels of noise. Magnetic data was collected with a GEMSys GSMP-35U UAV magnetometer. Data were logged at 10 Hz, and included GPS derived time and position, total magnetic field (nT) as well as x, y and z fluxgate magnetometer information and roll, pitch, heading information from a small Inertial Navigation System (INS) mounted on the aircraft floor. 
A magnetic base station, deployed close to Rothera Station, was used to correct for diurnal variations of the magnetic field. Prior to use the base station values were subject to the following corrections: i) DC correction to remove steps, associated with adjusting the base station support. A DC correction allows application of a uniform correction of a set value across the dataset ii) The base station data was detrended by a polynomial trend order of 8 to remove residual trends and the absolute average total field value. Iii) The data was then filtered by a mean filter with a window width of 40 (10 minutes) to remove residual high frequency noise. The base station data is also provided here for reference.
The raw airborne magnetic data was initially cleaned by manually removing extreme outliers and spikes. Next the magnetic data was filtered with a statical mean filter with a window width of 10 (1 second). Magnetic compensation was applied to account for adjustments of the UVA in term of aircraft roll, pitch and yaw, based on data from a triad of fluxgate magnetometers, also de-spiked and filtered at 1 second. Compensation was carried out in the software Aeromagnetic Compensation Postprocessing Application from GEMSys.
After compensation the total field magnetic survey data was corrected for the core field using the 2020 IGRF model, implemented in the Geosoft Oasis Montaj software. The magnetic data was levelled against ADMAP-2. Levelled ADMAP-2 data include a magnetic survey flown perpendicular to the SWARM survey. The ADMAP data was flown on two different altitudes at 2440 m and 1220 m. Therefore all data from SWARM and ADMAP-2 were upward continued to a constant altitude of 2440 m. Iterative levelling combined with removal of large outliers at the cross tie was applied until a satisfactory result (no artifacts in flight lines direction) was achieved. The levelled magnetic product was subtracted from the upward continued line data consisting of ADMAP-2 and SWARM data to obtain the levelling coefficients. Those coefficients are subsequently added to the SWARM line data at the original altitude. In doing so, the SWARM survey is levelled against ADMAP-2, while retaining the higher resolution that is achieved by a significant lower altitude.

Data is provided in two ASCII comma separated variable files. The primary file includes airborne magnetic data. The secondary file includes base station data. Dummy values are denoted by *. The primary airborne data set includes the following 16 columns:

flight_id: Flight number (Between 17 and 25).
line: line segment of given flight with constant flight heading.
projection_x_coordinate: X coordinate (meters) in polar stereographic projection. 
projection_y_coordinate: X coordinate (meters) in polar stereographic projection.
longitude: Longitude coordinate (degree).
latitude: Latitude coordinate (degree).
height_above_reference_ellipsoid: Flight elevation (meters). WGS1984 target ground clearance of 500 m.
date: Date (YYYY/MM/DD)
time_UTC: UTC time (HH:MM:SS.SS)
MagR: contains line data (nT) filtered by a 1 second mean filter and spike removed.
MagC: Magnetic data after compensation (nT).
RefField: Magnetic total field (nT) from the IGRF 2020 magnetic field data. Flight elevation channel used for elevation. Data and coordinate channels used for time and location.
MagRTC: Magnetic compensated and total field corrected data (nT).
Bcorr: Base station measured geomagnetic field variation (nT). Base station recorded from the 2024/01/29 to the 2024/03/05. Sampling rate: 4 measurements a minute (0.06Hz). Base station correction includes DC correction, detrend with a polynomial order of 8 and filtering with a 10-minute mean filter (Window width 40).
MagF: Final magnetic line product (nT). (MagRTC - Bcorr)
MagL: Levelled magnetic data product (nT). Data was levelled against ADMAP-2-line data.

The secondary base station dataset includes the following channels:
flight_id: Flight number (Between 17 and 25).
date: Date (YYYY/MM/DD)
time_UTC: UTC time (HH:MM:SS.SS)
mag_raw (nT):Raw base station measured total field.
DC (nT): Applied DC correction (nT)
mag_DC (nT): base value after DC correction (nT)
trend (nT):8th order polynomial trend through data.
mag_trend_shifted (nT): Base station value after removal of trend (nT)
mag_trend_shifted_mean_10min (nT): Applied base station correction (nT)
description: Sensor(s): GEMSys GSMP-35U UAV magnetometer
Platform(s):UAV - Windracers Ultra TD-02
description: After levelling the crossover error was 37.7 nT.

Data has 2 km line spacing. Along track resolution may be higher, but is limited by the distance to the nearest magnetic sources (&gt;500 m).