Locating animals from their sounds and tomography of the atmosphere: Experimental demonstration

Abstract

Calling animals are located using widely distributed receivers, and the sounds from the animals are used to map the sound speed and wind fields by means of tomography. In particular, two Red-Winged Blackbirds Agelaius phoeniceus are correctly located within a meter using recordings from five receivers spread over a 20×30-m2 region. The demonstration hinges on two new developments. First, a new algorithm for blindly estimating the impulse response of the channel is shown capable of estimating the differences in the time of first arrivals at two receivers. Since it is known that the first arrivals travel along nearly straight paths, the difference in time constrains the animal’s location to a hyperboloid, and the animal is located by intersecting hyperboloids from many pairs of receivers. Second, in order to accurately find the intersection point and map the sound speed and wind fields using tomography, a nonlinear equation is solved. The new algorithm for blindly estimating the impulse response of a channel offers a new way for locating sounds and making tomographic maps of the environment without any requirement for a model for the propagation of sound such as is needed for focalization, matched field processing, and conventional tomography.

Ray-theoretic localization of an impulsive source in a stratified ocean using two hydrophones

“…An approximate expression for the traveltime error arising from the straight-line assumption in the case of a linear sound-speed profile was derived by Spiesberger and Firstrup. 24,25 In a first attempt to take into account refraction effects in localization with two hydrophones, the assumption was made that the wave fronts corresponding to the direct arrivals at the two hydrophones are parallel to each other ͑same assumption for the surface-reflected arrivals͒. 20 This assumption is justified only in the case of very small hydrophone separations, which in turn limits the applicability to very short ranges, for which the ray bending effects are not significant anyway.…”

Linking the sounds of dolphins to their locations and behavior using video and multichannel acoustic recordings

“…Reflections of sound off the wall can confuse the localization algorithm. This problem with multipath is common among localization algorithms ͑e.g., Freitag and Tyack, 1993;discussion in Spiesberger and Fristrup, 1990;Spiesberger, 1999͒. Confusion is likely to be greatest when the sound originates near the wall and the reflected sound cannot be isolated from the direct path.…”

Self-organization of unattended wireless acoustic sensor networks for ground target tracking

“…When the SNR drops below SNR TH , the TDE error dramatically increases [16,17]. Since the acoustic localization system is a passive system, we do not have control on most of the parameters in (2).…”