A new global marine magnetic anomaly data set

Abstract

[1] The Geophysical Data System (GEODAS) stores more than 20 million magnetic measurements acquired over oceans and seas since the 1950s. Usually, the original total field (TF) and magnetic anomaly values are both stored. The anomaly results from the subtraction of the core and external magnetic field estimates from TF values. The most recent International Geomagnetic Reference Field models available at the time of the surveys were used to estimate the core field component (these models were revised later). External fields were estimated from magnetic observatory data. However, most of the measurements were not corrected for the external fields. Here we use comprehensive models to properly remove the core and external magnetic fields from all original TF measurements stored in the GEODAS. Besides, a track-by-track analysis of each data is necessary mainly to correct or to remove many shifted values as well as to reduce the noise in some track lines. Two additional processes are applied to obtain a data set coherent over the world. It includes an adjustment of long-wavelength magnetic anomalies using the National Geophysical Data Center (NGDC) -720 model, plus a line leveling method which mainly reduced some inconsistencies between different surveys. The root mean square of the crossover differences was reduced from 179.6 to 35.9 nT. Comparisons of magnetic anomaly maps before and after our treatment also highlight an improvement in the quality and the coherence of the data set. This study will serve to build a new World Digital Magnetic Anomaly Map.

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

“…National grids derived from aeromagnetic data are usually all of similar quality. Marine data are generally of lower quality than airborne data despite their re-levelling (Quesnel et al 2009). We therefore limit the overlap between two adjacent compilations to few tens of kilometres and, in some cases, avoid any overlap.…”

“…noaa.gov/mgg/geodas/trackline.html). These data have been carefully reprocessed by Quesnel et al (2009), who performed extensive data cleaning, removal of the core and external fields using the comprehensive model CM4 (Sabaka et al 2004), and line levelling. The data set produced by these authors (Quesnel et al 2009) has been the base of the WDMAM version 1 (Korhonen et al 2007) over the oceans.…”

“…These data have been carefully reprocessed by Quesnel et al (2009), who performed extensive data cleaning, removal of the core and external fields using the comprehensive model CM4 (Sabaka et al 2004), and line levelling. The data set produced by these authors (Quesnel et al 2009) has been the base of the WDMAM version 1 (Korhonen et al 2007) over the oceans. 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.…”

Geomagnetic field anomalies over the Lombok Island region: an attempt to understand the local tectonic changes

“…The subduction zones are indicated as black solid lines, while the dashed one indicates its presumed extension. This map is generated from cleaned and levelled marine magnetic data available from GEODAS for the interval 1950-2004(Quesnel et al 2009), combined with marine magnetic data along the Sunda-Banda Arc transition of BGR (Müller and Neben 2006) and aeromagnetic data of AIST and CCOP (Ishihara and Kisimaoto 2002). The white areas over oceans or islands, including that over the Lombok Island, indicate that no data are available.…”

“…Figure 2 shows a more detailed magnetic anomaly map over the islands along the Java Trench, including the Lombok Island. This map has been generated from cleaned and levelled marine magnetic data available from GEODAS for the interval 1950 -2004 (Quesnel et al 2009), combined with marine magnetic data along the Sunda-Banda Arc transition of BGR (Müller and Neben 2006) and aeromagnetic data of AIST and CCOP (Ishihara and Kisimaoto 2002). Figure 1 indicates that the Lombok Island is located between the centres of the highest negative-positive magnetic anomalies in this region, but the detailed map of Fig.…”