Inference of Fish Orientation From Broadband Acoustic Echoes.

摘要

A new method has been developed for inferring orientation of fish through the use of broadband acoustic signals. The method takes advantage of the small range resolution possessed by these signals, once temporally compressed through a cross-correlation process. The temporal resolution of these compressed signals is inversely proportional to the bandwidth, thus the greater the bandwidth, the finer the resolution. This process has been applied to broadband chirp signals spanning the frequency range 40-95 kHz to obtain a range resolution of approximately 2 cm (compressed down from the original unprocessed resolution of about 50 cm). With such a small resolution, individual scattering features along the fish have been resolved, especially for angles well off normal incidence. The duration of the compressed echo from live individual Alewife, as measured in a laboratory tank, is shown to increase monotonically with orientation angle relative to normal incidence. The increase is due to the increase in range separation between the echoes from the head and tail of the fish. The results of this study show that with a priori knowledge of the length of the fish, the orientation could be estimated from the duration of a single compressed broadband echo. This method applies to individual acoustically resolved fish and has advantages over previous approaches as it derives the orientation from a single ping and it does not use a.