ΔT–anomalies, DGRF 1980.0, 1000 m a.s.l

The database consists of 67 marine, surface and aerogeophysical surveying campaigns carried out between 1961 and 2008. The key element for the western German states is an aerial survey conducted by Prakla-Seismos between 1965 and 1971 at heights of 700 m asl (northern part), 1000 m asl (central part), and 1500 m asl (southern part). Line spacing of the aerial Survey was 2200 m; measurements were recorded approximately every 65 m along the north-south aligned lines. The measurements in the eastern German states were carried out by VEB Geophysik. The spatial resolution of the terrestrial measurements was up to 250 m. Aeromagnetic measurements were taken with typical line spacing of 250 m, although the separation between the measurement points along the aerial survey lines varied between 30 m to 70 m. The Leibniz Institute for Applied Geophysics (or its predecessor institutes) has carried out systematic subsequent measurements by itself or had them carried out on a contractual basis since 1985.This work was intensified primarily after 1990 to record the area covering the former inner-German border and regions around the border to the Netherlands. Surface measurements here were carried out with measurement point separations of 1000 m to 2000 m, whilst aeromagnetic survey lines were usually recorded at separations of 2000 m.

Converting the various datasets into the standard reference frames was undertaken by adding the total magnetic field at the time of each measurement, taking into consideration the secular variation related to the 1980.0 epoch, field continuation to 1000 m asl, and subtracting the new reference field. When integrating neighbouring data sets, care was taken to ensure that the differences in the overlapping zones were smaller than 5 nT. Measurements originally taken at 1000 m asl were used as references for this purpose.

The resulting anomalies in the geomagnetic total field vary from -720 nT to 1210 nT. In the high-resolution map now available, they show local structures such as the Vogelsberg Volcano, as well as regional tectonic units such as the Variscan crustal zone. The anomalies can provide information on the geological structure of the Earth's crust down to depths of at least 20 km.