ALBERT

Description: For frequencies above 30 mHz the instrument intrinsic noise level of typical fluxgate magnetometers used at geomagnetic observatories can mask ambient magnetic field variations on magnetically quiet days. This is especially true for stations located at mid- and low-latitudes where variations are generally smaller than at high latitudes. INTERMAGNET has set a minimum quality standard for definitive one second data. Natural field variations referred to as pulsations (Pc-1, Pc-2, Pi-1) fall in this 5 band. Usually their intensity is so small, that they rarely surpass the instrumental noise of fluxgate magnetometers. Moreover high quality magnetic field observations in the band 30 mHz–0.5 Hz contain interesting information, e.g. for the study of ionospheric electron interactions with electromagnetic ion cyclotron (EMIC) plasma waves. We propose a method to improve 1 Hz observatory data by merging data from proven and tested fluxgate magnetometers with induction coil magnetometers into a single data stream.We show how measurements of both instruments can be combined without information loss or phase distortion. The result is a time series of the magnetic field vector components, combining the benefits of both instruments: long term stability (fluxgate) and low noise at high frequencies (induction coil). This new data stream fits perfectly into the data management procedures of INTERMAGNET and meets the requirements defined in the Definitive One-second Data Standard. We describe the applied algorithm and validate the result by comparing power spectra of the fluxgate magnetometer output with the merged signal. Daily spectrograms from the Niemegk observatory (NGK) show that the resulting data series reveal information at frequencies above 0.05 Hz that can not be seen in raw fluxgate data.