Magnetotellurics (MT) is a passive geophysical method which uses natural variations of electromagnetic fields generated by global lightning discharges and ionospheric current systems. Since it is impossible to control these source fields, signal-to-noise ratios can be poor, particularly in presence of cultural electromagnetic noise such as power lines, railways, anti-corrosion currents in gas pipelines, etc. The Remote Reference (RR) technique is an effective way to improve magnetotelluric data quality by referencing the locally recorded electromagnetic fields to simultaneously collected, undisturbed fields at a remote reference site. Finding and maintaining such a reference site during a field campaign is expensive and time consuming. The permanent reference site in Wittstock is operated by the Geo-Electromagnetics working group of the GFZ within the framework of the Geophysical Instrument Pool Potsdam and offers high quality magnetic field recordings for RR processing free of charge for the EM community.
A permanent magnetotelluric (MT) remote reference station is located in an urban forest near the city of Wittstock, in north-eastern Germany (Eydam and Muñoz, 2011). It is equipped with two S.P.A.M. Mk IV data loggers and three sets of magnetometers working in different frequency ranges. The highest frequency data is recorded using Metronix MFS07 induction coils with a sampling frequency of 6.25 kHz. The high frequency data is recorded in quasi-continuous segments, with intervals of data being collected for 10 minutes at every hour. The intermediate, broad band magnetic field data are recorded continuously using Metronix MFS06 induction coils at 250 Hz sampling frequency. Finally, long period data is recorded using a 3-component Geomagnet Fluxgate magnetometer with 5 Hz sampling rate. For completeness, electric fields are also recorded continuously at the highest frequency.
The data are organized and available as daily folders. Data files are in EMERALD format (Ritter et al., 1998), which is also described in this document. We also provide computer code and example data demonstrating how to read these data files. The tools are provided as FORTRAN, C and C++ source codes and MATLAB scripts.