GEOMAGNETIC REPEAT STATION CRUSTAL BIASES AND VECTORIAL ANOMALY MAPS FOR GERMANY

Abstract

Geomagnetic repeat station data of Germany from 1964 to present have been studied to determine their accuracy and crustal biases. Like the data from geomagnetic observatories, repeat station data contain contributions from the regional and local crustal field, but their spatial density is by far not high enough to resolve such anomalies. Knowing this crustal bias, therefore, is important in using repeat station data to map or model the main field. To confirm the results obtained by using a global geomagnetic field model we constructed regional lithospheric field models using additional information from satellite and aeromagnetic data. The compatibility of the different data types is good and we present vectorial anomaly maps for Germany with a spatial resolution of approximately 37 km, which could be useful for future geological interpretation of magnetic anomalies. The anomalies contributing to the repeat station bias, however, can be of smaller scale and their amplitudes range up to absolute values of 177 nT in the north (X), 106 nT in the east (Y) and 176 nT in the vertical (Z) component. Average uncertainty estimates in the order of 5, 8 and 5 nT in X, Y and Z, respectively, are obtained from comparisons to a global model. The estimates, however, vary a lot between stations and components. The uncertainties should mostly result from measurement errors, insufficient elimination of external field contributions or relocations of stations which had been regarded as insignificant. There might also be a small contribution from insufficient description of secular variation in the global model used.