Comparison of global geomagnetic field models and evaluation using marine datasets in the north-eastern Atlantic Ocean and western Mediterranean Sea

Abstract Many models describing the Earth’s magnetic field exist and are maintained by international research organizations. However, no clear general overview of the cross-compared quality of these models is available. An evaluation of the internal component and of the anomaly field as estimated by a selection of nine geomagnetic models with global coverage is presented here. Anomaly field models are also compared with an external, independently processed marine dataset extracted from Shom’s (the French Hydrographic and Oceanographic Service) geophysical database. The comparative study shows that internal geomagnetic fields computed outside the provisional domain, up to degrees 12 or 13 of spherical harmonics (SH), can be considered as equivalent. Relative amplitude differences with the World Magnetic Model 2015 (WMM2015) and the 12th generation of the International Geomagnetic Reference Field (IGRF-12) taken as references are lower than 10 nT. For an extent reduced to the north-eastern Atlantic Ocean and western Mediterranean Sea, anomaly field models up to SH degree 720 and the 3rd version of the Earth Magnetic Anomaly Grid (EMAG2v3) at the equivalent 0.5° resolution are the closest models to the filtered marine data. However, they are significant spatial discrepancies and standard deviations of differences between models and data are about 65 nT. The 3-arc-minute World Digital Magnetic Anomaly Map (WDMAM) best reflects the unfiltered marine data, but with significant standard deviations of about 70 nT. Results demonstrate that any model can be used with insignificant errors to compute raw anomalies from total field measurements by removing the internal component of the Earth’s magnetic field. In addition, they suggest that the priority should be given to WDMAM for levelling and evaluating marine datasets and for computing enhanced high-resolution regional magnetic maps

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Additional file 2. Comparative statistical analysis of differences in inclination and declination values estimated (A) at a global scale reduced by 30° in latitude and 20° in longitude (grid spacing: 1°) and (B) for the NEAWM area (grid spacing: 0.5°)

MOESM1 of Comparison of global geomagnetic field models and evaluation using marine datasets in the north-eastern Atlantic Ocean and western Mediterranean Sea

Additional file 1. Comparative statistical analysis of differences in intensity values of the internal field (INT) estimated up to SH degrees 12 and 13 from global models (A) at a global scale reduced by 30° in latitude and 20° in longitude (grid spacing: 1°) and (B) for the NEAWM area (grid spacing: 0.5°)

MOESM4 of Comparison of global geomagnetic field models and evaluation using marine datasets in the north-eastern Atlantic Ocean and western Mediterranean Sea

Additional file 4. Comparative statistical analysis of differences in intensity values of the anomaly field (ANO) estimated up to SH degree 720 from HDGM2016 and EMM2015 and derived from EMAG2v3 and WDMAM (A) at a global scale reduced by 30° in latitude and 20° in longitude (grid spacing: 1°) and (B) for the NEAWM area (grid spacing: 0.5°)

MOESM3 of Comparison of global geomagnetic field models and evaluation using marine datasets in the north-eastern Atlantic Ocean and western Mediterranean Sea

Additional file 3. Maps of differences in inclination and declination values estimated from EMM2015 (A) and EMM2010 (B) and IGRF-12 (reference) models at a global scale reduced by 30° in latitude and 20° in longitude (grid spacing: 1°). Probably due to digital coding, the EMM2015 lithospheric model is doubtful for negative values of inclination and declination. Tests did not identify any problems for the previous version of the product (EMM2010)

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