Target localization aboard a tone emitting robotic echolocation system with mobile receivers

Abstract

Using only two receivers, animals are able to determine the location of a target in three dimensions. Echolocating bats, which employ broadband calls, have access to spectral cues that may be used, in conjunction with interaural disparities of intensity (IIDs) and/or time (ITDs), to encode a 3-D target angle. This work addresses the question: what cues might a tone-emitting echolocator employ to determine target azimuth and elevation? To this end, a 6-degree-of-freedom robotic sensor head was built to investigate the direction cues that might be generated by the systematic pinnae scanning movements used by many species of tone emitting bats. The first strategy investigated was the use of receiver motion to rotate the SONAR horizon through discrete IID sampling positions so that a 3-D target angle can be resolved across IID readings taken at two or more receiver positions. Next, the change in amplitude measured by continuously scanning pinnae was used to create temporal cues, which vary systematically with the target angle. In this scheme, angular resolution depends upon scan speed (ms) rather than interaural separation (microsecond). Finally, the use of Doppler shifts to encode the target angle through the cosine law was investigated.