A Mobile Geomagnetic Observatory

The Engineering Geoscience Group of the University of California at Berkeley has been active for the past few years in the measurement and interpretation of geomagnetic and geoelectric data in the range 10-3 to 10 Hz. To facilitate the acquisition of field data, as well as to develop a convenient, practical, and economic field procedure, the group has assembled a complete array of equipment into one large van, which, with its own power supply, can be quickly and easily moved from one site to another. The field sensors consist of three induction coils to measure field variations and expendable electrodes for earth-current measurements. Conventional amplifiers, integrators, and bandpass filters are used to treat the data prior to recording. To keep up with the development of advanced techniques of statistical analysis, the recording system has as its major unit a fourteen-channel digital incremental magnetic tape recorder capable of recording up to ten samples per second. An eleven-channel analog FM magnetic tape recorder is available for use when high-frequency field variations are present, and an analog paper chart record provides a means of continuously monitoring the activity throughout the experiment. Calibration is carried out on site with the use of a portable calibration coil. The digitally recorded data are in a simple format compatible with the computer facilities at Berkeley to permit rapid preliminary analysis while the equipment is still in the field.