Geomagnetism

EMAG3: NGDC's candidate for the World Digital Magnetic Anomaly Map

Marine and airborne magnetic anomaly data have been collected for more than half a century, providing global coverage of the Earth. Due to the changing main field from the Earth's core, and due to differences in quality and coverage, combining these data to a consistent global magnetic grid is challenging. The World Digital Magnetic Anomaly Map (WDMAM) project is an international effort to integrate all available near-surface and satellite magnetic anomaly data. Teams of researchers were invited by IAGA and CWGM to produce candidate maps using a common pool of data sets. Following a scientific review of the candidate submissions, NGDC's grid (now called EMAG3) was chosen as a base grid for the WDMAM project.

Fig.1: (click to enlarge) NGDC candidate for the World Digital Magnetic Anomaly Map. Plug-in files for NASA World Wind can be downloaded from GETECH .

The WDMAM is specified as a global 3-arc-minute resolution grid of the anomaly of the magnetic intensity at an altitude of 5 km above mean sea level. It was compiled from satellite, marine, aeromagnetic and ground magnetic surveys (see our acknowledgement of data providers and collaborators). A version of the WDMAM for visualization in NASA World Wind can be downloaded from GETECH . See table below for a plugin for Google Earth.

Available WDMAM Downloads
	Type	Format	Mbyte	Contents
	Full resolution map	PDF	38	World Digital Magnetic Anomaly Map as a full resolution image file
	Article	PDF	5	Reprint of our paper The NGDC candidate for the World Digital Magnetic Anomaly Map
	Google Earth	KMZ	5	Plugin for Google Earth. Requires installation of Google Earth. Open this KMZ file with Google Earth, then look under "Places" and check "NGDC World Magnetic Anomaly Map".
	xyz/zip	zipped ascii	142	Ascii grid of the magnetic total intensity at 5km above mean sea level. See Maus et al. (2007) for flag codes used in column 4.
	xyz	plain ascii	855	Ascii grid of the magnetic total intensity at 5km above mean sea level. See Maus et al. (2007) for flag codes used in column 4.
	xyz.gz	zipped ascii	42	NGDC marine magnetic trackline data at sea level after line-leveling. For our candidate map these data were combined with the Project Magnet data at a common altitude of 5 km above mean sea level.
	xyz.gz	zipped ascii	10	Project Magnet aeromagnetic data at the original flight altitude (about 5 km) after line-leveling. For our candidate map these data were combined with the NGDC trackline data at a common altitude of 5 km above mean sea level.

Stefan Maus