Index of content:
Volume 119, Issue 5, May 2006
- ACOUSTIC SIGNAL PROCESSING 
Accuracy of an acoustic location system for monitoring the position of duetting songbirds in tropical forest119(2006); http://dx.doi.org/10.1121/1.2184988View Description Hide Description
A field test was conducted on the accuracy of an eight-microphone acoustic location system designed to triangulate the position of duetting rufous-and-white wrens (Thryothorus rufalbus) in Costa Rica’s humid evergreen forest. Eight microphones were set up in the breeding territories of 20 pairs of wrens, with an average intermicrophone distance of . The array of microphones was used to record antiphonal duets broadcast through stereo loudspeakers. The positions of the loudspeakers were then estimated by evaluating the delay with which the eight microphones recorded the broadcast sounds. Position estimates were compared to coordinates surveyed with a global-positioning system(GPS). The acoustic location system estimated the position of loudspeakers with an error of and calculated the distance between the “male” and “female” loudspeakers with an error of . Given the large range of distances between duetting birds, this relatively low level of error demonstrates that the acoustic location system is a useful tool for studying avian duets. Location error was influenced partly by the difficulties inherent in collecting high accuracy GPS coordinates of microphone positions underneath a lush tropical canopy and partly by the complicating influence of irregular topography and thick vegetation on sound transmission.
119(2006); http://dx.doi.org/10.1121/1.2188667View Description Hide Description
The problem of imaging the intensity distribution of a subsurface acoustic source from passive measurements is considered. The source may be spatially extended, and is assumed to be random and spatially incoherent. Two passive imaging algorithms are examined and shown to be closely related. The first algorithm is based on time-domain migration in which signals recorded by an array of receivers are backpropagated to multiple source locations. The second algorithm is based on backprojecting cross-correlating signals computed between all pairs of receiving elements. When the latter algorithm is applied in two dimensions, the correlation peak can be shown to be the line-integral of the source intensity along a hyperbolic path whose foci are the receiving points. This suggests a filtered-backprojection procedure in which the backprojection is performed along multiple hyperbolic paths. The algorithm is easily generalized to three dimensions, in which the cross-correlated signals are backprojected over hyperboloids. Images using simulated and field data are presented as an illustration.