# Network of sensitive magnetometers for urban studies

## TL;DR

This paper presents a distributed magnetometer network in Berkeley for urban magnetic environment monitoring, demonstrating hardware, software, and initial findings including BART transit signals and lightning events.

## Contribution

It introduces a novel geographically distributed magnetometer network with synchronized data collection and analysis methods for urban magnetic studies.

## Key findings

- BART transit signals are the dominant magnetic feature.
- Lightning strikes are detected as anomalous magnetic events.
- Strong weekday-weekend magnetic variations are observed.

## 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.