Abstract:

An acoustic tracking/telemetry/data-logging system is being developed for real-time monitoring of underwater movements and behaviors of free-ranging whales from a vessel. This system consists of an acoustic transponder ``tag'' attached to the animal. Upon interrogation from a ``surface'' station, the transponder produces a high-frequency (38-kHz) signal. An array (either short or ultrashort base line) of transducers at the surface station receive and compute the underwater location of the tag. Locations are computed based on the return time and time or phase delay of the received signal. Multiple tags can be monitored simultaneously and relative underwater positions can be integrated with data from a GPS on the tracking vessel (resulting in a latitude, longitude, and depth). A microprocessor on the tag controls basic functions and can be programmed to record and store up to seven channels of data from attached sensors (e.g., water temperature, velocity, etc). Data are stored internally on the tag's RAM memory or can be telemetered acoustically to the surface station. Preliminary field testing in the open ocean resulted in an effective range of over 1 km. This system is being developed for determining movements and eventually acoustic behaviors of individual blue and fin whales. [Work supported by ONR.]