Low-frequency acoustic monitoring in urban environments

Abstract

Arrays of infrasound sensors are commonly deployed in quiet rural settings to monitor high energy/low-frequency sources at distances of hundreds to thousands of kilometers. Advancements in infrasound sensor technology allow for measurement across the acoustic spectrum from infrasound (< 20 Hz) to low end audible (< 1000 Hz). This supports a growing interest in using infrasound arrays to monitor low energy/higher frequency sources at local propagation distances (<100 km). Examples of these sources include vehicles (ground and air), small explosions, and infrastructure (e.g., bridges). Many of these sources are driven by anthropogenic activity. In order to successfully monitor them, arrays of sensors will need to be installed closer to the sources of interest, thereby requiring arrays to encroach on urban spaces. The design, deployment, and utilization of these arrays will face challenges, such as limited open ground for installation and source signals that need to be separated from a complex acoustic noise field to be observed. This presentation shares techniques for instrumenting the urban environment and characterizing the ambient acoustic fields in three different urban environments. [Permission to publish was granted by the Director, Geotechnical and Structures Laboratory, U.S. Army Engineer Research and Development Center.]