The Acousonde: A miniature autonomous wideband recorder.

Abstract

The Acousonde™ is a newly designed miniature acoustic/ultrasonic recording tag incorporating several improvements over its predecessor, the Bioacoustic Probe. Design trade-offs for its acoustic data paths targeted acquisition of both near and distant odontocete echolocation clicks with minimal distortion while preserving general-purpose utility and low-power operation. Two acoustic channels are available: a low-power channel for long-term recording of signals up to 9 kHz and a high-frequency channel for signals up to 100 kHz. Each channel has its own dedicated hydrophone. For antialiasing, the low-power channel uses an adjustable switched-capacitor elliptic filter, while the high-frequency channel uses a fixed-frequency linear-phase filter; both filters may be bypassed if raw acquisition is desired. “Ping-pong” alternating sampling may be used to acquire samples from both channels concurrently, possibly to assess time-of-arrival differences between the two hydrophones. The controlling microprocessor, an ARM 9 with vector floating point accelerator, can digitally filter and downsample acoustic data during acquisition to reduce storage requirements. Other sensors include a 3D accelerometer, a 3D compass, a depth transducer, and a temperature monitor. Eight gigabytes of data storage are available, with data offload via a MicroUSB connector. Initial tests with captive animals are planned shortly. [Work supported by ONR.]