DOI: 10.5285/410ee2f9-2d22-4155-aaed-43b93a7c3d62
title: Aeromagnetic survey across the Brunt Ice Shelf, 2017

description: This data set contains aeromagnetic data collected opportunistically during an airborne radar survey of the Brunt Ice Shelf as part of the NERC/BAS Life Time of Halley project. The survey was flown draped with an average height above the ice surface of 420 m, and includes 4716 km of new data. The aircraft used was the BAS aerogeophysically equipped twin otter VP-FBL. Data are available include all data streams from raw to fully processed, following the ADMAP 2 naming convention, and are provided in both Geosoft database (.gdb) and ASCII file formats (.xyz). Base station data is also provided.
The Brunt 2017 survey was carried out as part of the NERC/BAS Life Time of Halley project, and subsequent data processing was supported by the BAS Geology and Geophysics team. In addition we thank the BAS air unit and staff at Halley Research Station for their support of the 2017 field campaign.
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. Data was recorded at 10 Hz on a PicoEnvirotec logging system, before being decimated to 1 Hz for subsequent processing. Additional base station information from a calibrated long-term fluxgate sensor at Halley Station was used during data processing.
Raw line aeromagnetic data from the 2017 Brunt Survey were corrected for the regional geomagnetic field (IGRF) and diurnal variations recorded by the Halley VI magnetic fluxgate base station. Base station corrections were 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. Additional corrections for offsets induced by aircraft operations and flight heading direction were also applied. Note magnetic compensation was not carried out as the opportunistic nature of the dataset did not allow for a suitable calibration flight.
To further improve the levelling of the 2017 Brunt aeromagnetic survey data from ICEGRAV 2013 survey (Forsberg et al., 2017) was also considered, but is not included in this data download. Magnetic data from both surveys were continued to a common altitude of 500 m. To minimize errors due to downward continuation data were filtered with a low pass filter two times the downward continuation distance. After continuation the data were statistically levelled to minimize survey to survey offsets and residual errors along individual lines.
description: The standard deviation of the crossover error of the final statistically levelled dataset was 8.21 nT for 313 intersections, after removing 9 anomalously high (&gt;30 nT) crossover values.  Resolution: The line spacing for the main survey area is 5 km, with regional lines spaced ~18 km apart.  The provided data is sampled at 1 Hz, which equates to a 60 m along track sample spacing.
Data is provided in one of two formats: Geosoft database (.gdb) with associated .dbview file, or ASCII file format (.xyz). The data contains the following channels:
(1) "Line No." - Sequential line number through survey.
(2) "LON"	- Longitude (decimal degrees, WGS84).  Recorded GPS positions - no post processing.
(3) "LAT" - Latitude (decimal degrees, WGS84).
(4) "X" - Projected Polar Stereographic coordinate (m). Standard parallel -71.
(5) "Y" - Projected Polar Stereographic coordinate (m).
(6) "ELEV" - Flight elevation (meters).  WGS84 elipsoid. 
(7) "DATE" - Date (YYYY/MM/DD).
(8) "TIME" - UTC time (HH:MM:SS.SS).
(9) "MagR" - Raw total field magnetic observation (nT).
(10) "Tcorr" - Tiptank correction (nT), includes DC shifts due to aircraft noise.  Dummy values recorded in areas where data is considered unreliable.
(11) "RefField"	- Geomagnetic reference field value (nT).
(12) "MagRTC" - Magnetic value adjusted for the Tiptank and geomagnetic field values.   (MagRTC) = (MagC) + (Tcorr) - (RefField) 
(13) "Bcorr" - Base station measured geomagnetic field variations (nT). 
(14) "MagBRTC" - (MagBRTC) = (MagRTC) - (Bcorr)
(15) "Acorr" - Additional corrections (nT) for heading error.  
(16) "MagF" - Final mag value (nT) after all corrections and prior to any levelling.  (MagF) = (MagBRTC) + (Acorr) 
(17) "MagL" - Levelled mag value (nT). Two passes of statical levelling, with an imposed trend of order 0 or 1. Note prior to levelling data was continued to a uniform altitude of 500 m.

The base station dataset includes the following channels:
(1) "DATE" - Date (YYYY/MM/DD)
(2) "TIME" - UTC time (HH:MM:SS.SS)
(3) "nT_total" - Total field calculated from fluxgate components (nT)
(4) "Mag_base" - Total field minus mean base value (42488.87) (nT)
(5) "Mag_base_30_min" - Base station value with 30 minute filter