Design of Infrasonic Arrays

Abstract

The Infrasound Experts Group of the Geneva Conference on Disarmament Ad Hoc Committee on a Nuclear Test Ban has recommended an infrasound array design consisting of four elements, with three elements forming an equilateral triangle and the fourth at the center of the triangle. The Experts recommended that the sides of the triangle be in the range 1 to 3 km. In this report, in an attempt to place constraints on the array aperture, we evaluate the beamforming azimuthal estimation error of such arrays and compare it to historical data on observed azimuth residuals. The analysis for perfectly correlated signals shows that for beam signal-to-noise » 1 the rms error is proportional to wavelength and inversely proportional to array aperture, beam amplitude signal-to-noise, and the square root of the time-bandwidth product. For beam signal-to-noise « 1 the relations are the same except that the rms error is inversely proportional to the square of the amplitude signal-to-noise.

Automatic infrasound detection and location of sources in the western United States

“…The lack of broad correlation between mining events and infrasound sources may reflect a combination of the seasonal variations in the winds, the limited station distribution, as well as the possibility of reduced atmospheric infrasound coupling from some types of mining explosions. Further, signal detection might have been degraded by the lack of signal correlation between array elements for higher frequency signals [ Christie and Campus , ; Blandford , ]. Additionally, if these signals have frequencies at or above 4 Hz, they may not have been detected because the amplitude of high‐frequency infrasound decays more rapidly with distance.…”

“…The lack of events in these areas could be because there are few sources which preclude arrivals at the stations, or the average distance to nearby arrays is large and the accompanying signals are attenuated. Since signal correlation between array elements has been shown to decrease with increasing source‐receiver distance and with increasing frequency [ Blandford , ], one would expect to detect a smaller number of signals at larger distances. In order to quantify array coverage, the average distance from the closest three stations to each grid point across the study area is estimated and contoured (Figure ).…”

Understanding and Designing Military Organizations for a Complex Dynamic Environment

“…Azimuth is measured from north. The calculations are based on Δc = 15 m/s and Δθ = 5° as found by Blandford (1997). 24…”

Detection of Nuclear Explosions Using Infrasound Techniques

“…Azimuth is measured from north. The calculations are based on Δc = 15 m/s and Δθ = 5° as found by Blandford (1997). 20.…”

“…Results are shown in blue for a 1.0-km aperture array; in green for a 2.0-km aperture array and in red for a 3.0-km aperture array. The correlation model parameters are Δc = 15 m/s and Δθ = 5° (Blandford, 1997). 31…”