Title: Network of sensitive magnetometers for urban studies,
Abstract: The magnetic signature of an urban environment is investigated using a
geographically distributed network of fluxgate magnetometers deployed in and
around Berkeley, California. The system hardware and software are described and
results from initial operation of the network are reported. The sensors sample
the vector magnetic field with a 4 kHz resolution and are sensitive to
fluctuations below 0.1 $\textrm{nT}/\sqrt{\textrm{Hz}}$. Data from separate
stations are synchronized to around $\pm100$ $\mu{s}$ using GPS and computer
system clocks. Data from all sensors are automatically uploaded to a central
server. Anomalous events, such as lightning strikes, have been observed. A
wavelet analysis is used to study observations over a wide range of temporal
scales up to daily variations that show strong differences between weekend and
weekdays. The Bay Area Rapid Transit (BART) is identified as the most dominant
signal from these observations and a superposed epoch analysis is used to study
and extract the BART signal. Initial results of the correlation between sensors
are also presented.