Abstract:
Acoustic and seismic sensors have good potential for passive, non‐line‐of‐sight, detection, localization, and monitoring of natural and human activities. However, to fulfill this potential, sensor algorithms must be designed to not only robustly identify signals of interest but also to cope with environmental effects including high levels of background noise often found in urban areas. This paper presents experimental measurements conducted in Baltimore and at other locations to investigate noise levels in rural, urban, and industrial environments for audio frequencies between 6 Hz and 20 kHz and seismic frequencies from 6 to 1000 Hz. Because of the interest in large‐scale Earth studies, there are hardly any previous seismic measurements in this high‐frequency band and also most were done in remote areas specifically to avoid cultural noise. The measured urban seismic spectra tend to have more structure and variation in shape from one location to another compared to the acoustic spectra, and a more rapid decay with increasing frequency, usually about 30 dB from 30 to 600 Hz. The urban acoustic peak frequency is usually around 60 Hz, while the peak seismic frequencies are usually less than 25 Hz. [Work funded by U.S. Army.]