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

Calling animals are located using widely distributed receivers, and the sou nds from the animals are used to map the sound speed and wind fields by mea ns of tomography. In particular, two Red-Winged Blackbirds Agelatius phoeni ceus are correctly located within a meter using recordings from five receiv ers spread over a 20 by 30 m region. The demonstration hinges on two new de velopments. First, a new algorithm for blindly estimating the impulse respo nse of the channel is shown capable of estimating the differences in the ti me of first arrivals at two receivers. Since it is known that the first arr ivals travel along nearly straight paths, the difference in time constrains the animal's location to a hyperboloid, and the animal is located by inter secting hyperboloids from many pairs of receivers. Second, in order to accu rately find the intersection point and map the sound speed and wind fields using tomography, a nonlinear equation is solved. The new algorithm for bli ndly estimating the impulse response of a channel offers a new way for loca ting sounds and making tomographic maps of the environment without any requ irement for a model for the propagation of sound such as is needed for foca lization and matched field processing. (C) 1999 Acoustical Society of Ameri ca. [S0001-4966(99)00108-3].