Modeling and development of a narrowband gas-combustion infrasound source

Abstract

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 development of a well-controlled narrowband infrasound source with frequency capabilities over the 0.1 to 10.0 Hz band. Design of a transportable sound source within this band is a difficult engineering challenge. The simple source equation, which will govern any portable 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 at equal range. To combat this, the authors have developed a source system that uses gas combustion to displace large volumes in the open atmosphere using the gaseous and highly heated combustion constituents of propane and atmospheric oxygen. Measurements have verified the capability of generating narrowband signals with reasonable signal-to-noise ratio (SNR) over the full band at close range. Signals at 1 Hz have been measured with reasonable SNR to ranges greater than 2 km. Development of the infrasound source prototype, experimental measurements, and modeling of the acoustic pressure output will be discussed.