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

Didier Rouxel,Marie-Françoise Lequentrec-Lalancette,Jean-François Oehler

doi:10.1186/s40623-018-0872-y

Didier Rouxel, Marie-Françoise Lequentrec-Lalancette + Show 1 more

Open Access

https://doi.org/10.1186/s40623-018-0872-y

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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.

Highlights

Global geomagnetic models mathematically describe the Earth’s magnetic field
We have presented a comparison of nine global geomagnetic models and their evaluation using an external marine dataset processed according Service Hydrographique et Océanographique de la Marine (Shom)’s methodology
The World Magnetic Model 2015 (WMM2015), EMM2015, HDGM2016, Potsdam Magnetic Model of the Earth (POMME)-9, CM4 and International Geomagnetic Reference Field (IGRF)-12 models quite reflect the internal component of the geomagnetic field with relative differences in intensity value of less than 10 nT

Summary

Introduction

Global geomagnetic models mathematically describe the Earth’s magnetic field (see Langel 1987; Backus et al 1996). The International Geomagnetic Reference Field (IGRF, Table 1) is the reference model adopted by the scientific community to correct the main field and derive magnetic anomalies. Global anomaly field models, such as the Earth Magnetic Anomaly Grid (EMAG) or the World Digital Magnetic Anomaly Map (WDMAM) (Table 1), are used to level and evaluate marine datasets. They can be used for computing enhanced regional magnetic maps

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