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 initial operations of the network are reported. The sensors measure vector magnetic fields at a 3960 Hz sample rate and are sensitive to 0.1 $\mathrm{nT}/\sqrt{\mathrm{Hz}}$. Data from individual stations are synchronized to ±120 µs using global positioning system (GPS) and computer system clocks and automatically uploaded to a central server. We present the initial observations of the network and preliminary efforts to correlate sensors. A wavelet analysis is used to study observations of the urban magnetic field over a wide range of temporal scales. The Bay Area Rapid Transit (BART) is identified as the dominant signal in our observations, exhibiting aspects of both broadband noise and coherent periodic features. Significant differences are observed in both day–night and weekend–weekday signatures. A superposed epoch analysis is used to study and extract the BART signal.

中文翻译：

---

用于多尺度城市科学和信息学的磁力计网络

使用在加利福尼亚州伯克利及其周围地区部署的磁通门磁力计的地理分布网络，研究了城市环境的磁信号。描述了系统硬件和软件，并报告了网络的初始操作。传感器以3960 Hz的采样率测量矢量磁场，对0.1敏感 $\mathrm{T}/\sqrt{\mathrm{赫兹}}$。使用全球定位系统（GPS）和计算机系统时钟，来自各个站的数据同步到±120  µs，并自动上传到中央服务器。我们介绍了网络的初步观察和相关传感器的初步工作。小波分析用于研究大范围时间尺度上城市磁场的观测结果。在我们的观测中，湾区快速运输（BART）被确定为主要信号，同时展现了宽带噪声和相干周期特征。在白天和晚上以及周末和工作日的签名中都观察到了显着差异。叠加历元分析用于研究和提取BART信号。