An invaluable tool in characterization of any receiver, propagation path, or detection system, is a source with known and repeatable signal characteristics. This talk will discuss engineering development and evaluation of a coherent (non-explosive, periodic, with controlled duration) infrasound source with frequency capabilities in the sub-hertz to several hertz band. Design of a sound source within this band is a difficult engineering challenge. The simple source equation, which will govern any portable human-fabricated infrasound source due to the long wavelengths, shows this fundamental difficulty. As frequency decreases volume displacement must increase by the squared inverse factor of frequency in order to maintain an equal pressure amplitude at equal range. For this reason, the authors evaluate utilizing the high energy density available in gas combustion to periodically displace large volumes of air within the open atmosphere. Prototype testing has verified the capability of generating continuous signals at a fundamental frequency of 0.25 Hz at ranges >1 km in low wind conditions. Generation of harmonics of this fundamental throughout the 0.25-4.0 Hz band with reasonable signal-to-noise ratio was also demonstrated. These results will be reviewed, and efforts to increase useful source range will be discussed.
Development of a cost effective and transportable non-explosive infrasound source to aid in verification of infrasound monitoring sites.