A network of magnetometers for multi-scale urban science and informatics
Geoscientific Instrumentation, Methods and Data Systems
<p><strong>Abstract.</strong> 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&thinsp;Hz sample rate and are sensitive to 0.1&thinsp;<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML"
... /1998/Math/MathML" id="M1" display="inline" overflow="scroll" dspmath="mathml"><mrow><mrow class="unit"><mi mathvariant="normal">nT</mi></mrow><mo>/</mo><msqrt><mrow class="unit"><mi mathvariant="normal">Hz</mi></mrow></msqrt></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="43pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="13dddfff74044c671764fd403f396a32"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="gi-8-129-2019-ie00001.svg" width="43pt" height="14pt" src="gi-8-129-2019-ie00001.png"/></svg:svg></span></span>. Data from individual stations are synchronized to <span class="inline-formula">±120</span>&thinsp;<span class="inline-formula">µs</span> 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.</p>