Magnetics Data from the Escanaba Trough (Gorda Ridge)

Magnetics data was collected by a three-component fluxgate magnetometer attached the autonomous underwater vehicle (AUV) Sentry during the TN403 expedition in the Escanaba Trough on the R/V Thomas G. Thompson. The expedition occurred between May 24, 2022, and June 13, 2022, and was led and staffed by USGS employees.

Magnetics data were compiled and cleaned upon returning to land. To remove the magnetization effects from the AUV, a full-vector calibration was performed, which involved spinning the AUV in the water column to complete at least one 360-degree rotation. The attitude and vector magnetic field data from these rotations were used to calculate the induced and permanent magnetization of the AUV using a least-squares solution and subsequently removed from the raw data. The resulting files from this initial calibration are, which also include raw data columns: escanaba_d638_mag.csv; escanaba_d639_mag.csv; escanaba_d640_mag.csv; escanaba_d641_mag.csv; escanaba_d642_mag.csv; escanaba_d643_mag.csv; escanaba_d646_mag.csv; escanaba_d647_mag.csv. The calibration matrices used in the full-vector calibration are included in the file Calibration_Coefficient_Matrices.txt. To further prepare the vector magnetic data for the inversion modelling the data were: (1) low-pass filtered with a passband frequency of 0.01 Hz at a data frequency of 10 Hz; (2) projected to WGS 1984 UTM Zone 9N; (3) separated into single survey lines with the ends of the lines where the AUV turned around removed, each line was levelled to its survey's tie line(s); (4) further linear heading corrections were calculated and applied to each individual survey line, to remove artifacts left over from the full-vector calibration; (5) a 50 m moving mean was applied to the data along each survey line, and then the data was subsampled to a 50 m data point spacing; (6) the survey lines were combined into new survey groups, with dive 643's data being separated into two surveys, d643_1 and d643_23, and dive 638, 640, and 641 were combined into a single group; and (7) the Earth's field strength was calculated at each survey location using the WMM-2020 model (https://www.ngdc.noaa.gov/geomag/calculators/magcalc.shtml#igrfwmm), and was subtracted from the data to produce a TMI anomaly. The resulting data files are: d638_mag_lvled_50m_UTM9N.csv; d639_mag_lvled_50m_UTM9N.csv; d640_mag_lvled_50m_UTM9N.csv; d641_mag_lvled_50m_UTM9N.csv; d642_mag_lvled_50m_UTM9N.csv; d646_mag_lvled_50m_UTM9N.csv; d647_mag_lvled_50m_UTM9N.csv.