Measurements of BART magnetic fields with an automatic geomagnetic pulsation index generator

Measurements of the large-amplitude magnetic field fluctuations produced by the San Francisco Bay Area Rapid Transit (BART) system using an automatic computer-based geomagnetic pulsation index generator located on the Stanford campus, which is approximately 40 km from the center of the BART system, are described. Because the temporal variation of the fluctuations is well defined on an hour-to-hour and day-to-day basis, due to the transit system scheduling, they provide a convenient means for evaluating the performance of the index generator. The index generator, in turn, provides new information about the frequency content of the BART field fluctuations, and it can be used, in a general sense, to monitor activity on the BART system