Building the second version of the World Digital Magnetic Anomaly Map (WDMAM)

Yujin Choi,Jérôme Dyment,Vincent Lesur,Mohamed Hamoudi,Erwan Thébault

doi:10.1186/s40623-016-0404-6

Abstract

The World Digital Anomaly Map (WDMAM) is a worldwide compilation of near-surface magnetic data. We present here a candidate for the second version of the WDMAM and its characteristics. This candidate has been evaluated by a group of independent reviewers and has been adopted as the official second version of the WDMAM during the 26th general assembly of the International Union of Geodesy and Geomagnetism (IUGG). The way this compilation has been built is described with some details. A global magnetic field model of the lithosphere contribution, parameterised by spherical harmonics, has been derived up to degree and order 800. The model information content has been evaluated by computing local spectra. Further, the compatibility of the anomaly field displayed by the WDMAM with a pure induced magnetisation is tested by comparison with the main field strength. These studies allowed an analysis of the compilation in terms of strength and wavelength content. They confirm the extremely smooth and weak contribution of the magnetic field generated in the lithosphere over Western Europe. This apparent weakness possibly extends to the Northern African continent. However, a global analysis remains difficult to achieve given the sparseness of good quality data over very large area of oceans and continents. The WDMAM and related information can be downloaded at http://www.wdmam.org/.

Highlights

The World Digital Magnetic Anomaly Map (WDMAM) task force is part of the working group V-mod of the International Association of Geomagnetism and Aeronomy (IAGA)
The predominant feature of the WDMAM candidate map shown in Fig. 1 is the strength of the lithospheric anomaly field over Siberia and North America
In this paper, we have described the derivation of the second version of the World Digital Magnetic Anomaly Map (WDMAM)

Summary

Introduction

The World Digital Magnetic Anomaly Map (WDMAM) task force is part of the working group V-mod of the International Association of Geomagnetism and Aeronomy (IAGA). We use the same data set, complemented by additional marine data made available by NOAA between 2006 and 2010 and processed in the same way (Takemi Ishihara and Manuel Catalan, personal communication, 2011), as the base of the WDMAM version 2 over the oceans. It is practically impossible to account for the anomalies of neighbouring countries, and the long wavelengths of a merged grid of several aeromagnetic and marine data sets are necessarily wrong.

Results

Conclusion