Using “phantom” echoes to study dolphin biosonar

Biosonar studies have greatly benefited from the use of electronic, or “phantom,” echoes. In this paradigm, amplitude and timing information are extracted from an emitted biosonar pulse, then a delayed signal is broadcast to the animal to appear as an echo from a more distant target. Phantom echoes provide unique capabilities for studying biosonar, since they allow echo features such as amplitude and delay to be independently manipulated. In 1987, Whit Au and colleagues described a phantom echo system for use with marine mammals [Au et al. (1987). “Phantom electronic target for dolphin sonar research,” J. Acoust. Soc. Am. 82, 711-713]. In this system, delayed broadcasts of one or more replicas of the dolphin click were triggered by dolphin click emissions. A major improvement in phantom echo systems was later described by Aubauer and Au (1998) [“Phantom echo generation: A new technique for investigating dolphin echolocation,” J. Acoust. Soc. Am. 104, 1165-1170], who simulated the impulse response of a physical target, rather than broadcasting a stereotyped waveform. In this talk, phantom echo system concepts are briefly presented and several recent applications of phantom echo systems—inspired by the work of Aubauer and Au—are discussed. [Work supported by ONR.]