Infrasound monitoring in non-traditional environments

To date, the infrasound community has avoided deployments in noisy urban sites because interests have been in monitoring distant sources with low noise sites. As monitoring interests expand to include low-energy urban sources only detectable close to the source, case studies are needed to demonstrate the challenges and benefits of urban infrasound monitoring. This case study highlights one approach to overcoming urban challenges and identifies a signal's source in a complex acoustic field. One 38 m and one 120 m aperture infrasound arrays were deployed on building rooftops north of downtown Dallas, Texas. Structural signals in the recorded data were identified, and the backazimuth to the source determined with frequency-wavenumber analysis. Fourteen days of data were analyzed to produce 314 coherent continuous-wave packets, with 246 of these detections associated with a narrow range of backazimuth directions. Analyzing the backazimuths from the two arrays identified the Mockingbird Bridge as the probable source which was the verified with seismic measurement on the structure. Techniques described here overcame the constraints imposed by urban environments and provide a basis to monitor infrastructure and its conditions at local distances (0-100 km).