The MATS system is based around a multibeam sonar. We have field tested the Simrad SM2000 Multibeam Sonar with 180-degree head for this purpose (November field trial). The SM2000 operates at 200kHz, has 128 electronically focused returing beams that cover a 180 swath of the ocean that is either 20 or 1.5 degrees wide. Each beam is subdivided into 782 intervals, and the backscatter strength in each interval of each beam is digitally recorded.

The SM2000 has principally been used for detailed bottom mapping and quantitative midwater fisheries assessment.

The sonar head will be mounted onto heavy duty Pan and Tilt unit that will allow the sonar head to be remotely positioned. The PT-25 (ROS, Inc) can rotated 170-degrees CW and CCW in the horizontal and vertical directions.

In order to know where the sonar head is pointing at all times, we will also need to incorporate information on boat motion. The digital output from a Gyroscopic / inertial sensor will be incorporated into header information of the multibeam images.

The initial analyses of the backscatter data from the multibeam sonar head will be analyzed using EchoView 3.1 Fisheries Acoustic Software with all appropriate modules. We will work with Ian Higginbottom to incorporate boat motion and positioning information into Echoview's analytical functions.

Additional, purpose built software, will be designed by Larry Mayer and colleagues at the University of New Hampshire

VHF tags will be deployed on animals to facilitate locating them over large distances (~5km range). Tags will be glued to the fur with quick-setting marine epoxy. Tags will be located using direction finding receiver with 4 Yagi antennas, mounted onto the research vessel

Venus Underwater Video Cameras, manufactured by Wild Insight will be deployed on the head of the animals to record images of prey. The cameras have been successfully used on fur seals to record foraging on krill

Underwater ultrasonic transmitters, or "pingers" are currently commercially available (Vemco, Benthos, etc.) and can be deployed on animals to aid in their location when underwater. Animals outfitted with these tags can be located using an underwater hydrophone, or by multibeam sonar, when operating in passive mode. Unfortunately, they can no be used to uniquely identify animals if the sonar is in active mode. For that application, we must develop transponding tags.

 Transponders are tags that emit a pulse in response to signals from the multibeam sonar. As a result, they can be seen on the multibeam image when the sonar is operating in active mode. These tags would allow us to track and uniquely identify animals in the sonar image.

The image is of a  prototype transponder we have been working to develop.

An Encoded Micro-Transponder For Ultrasonic Tracking of Underwater Targets

Albert W. Franzheim III¹, Christian de Moustier², and J. Ward Testa³

¹ University of New Hampshire, Durham, NH 03824,
² Heat, Light & Sound Research, Inc., La Jolla, CA 92037
³NOAA Alaska Fisheries Science Center, Ankorage, AK 99508

The prototype of a miniature underwater acoustic transponder has been designed and built to track in real-time the movements of objects or animals in the water column.  Initial design constraints included tracking Weddell seals while they forage in a fish school.  The data storage tags currently used for uniquely identifying and tracking underwater targets do not provide interrogation and data dissemination capabilities in a form factor and acoustic frequency band acceptable for tracking seals and other species, and it is necessary to physically recover the tags to obtain the data. 

The prototype micro-transponder is the size of a matchbook (~L:50 mm ´ W:37 mm ´ H:10 mm) and it operates in an acoustic frequency band of 150-170 kHz, which is above the known hearing frequency band of marine mammals.  The transponder is powered by an internal lithium battery that provides enough energy for a deployment duration of 2-3 days with a 0.1% duty cycle.  The transmit and receive circuitry has been scaled to send and detect sound at a maximum range of 750-800 meters.  A printed circuit board has been assembled with all of the circuitry for the transponding functionality including a micro-controller, which allows firmware to be updated for additional adaptability and capabilities, such as encoding ambient temperature and pressure in the reply signal. The prototype micro-transponder has been tank tested for validation of its functionality.  Preliminary work shows that this micro-transponder will be a viable solution for tracking animals in their natural underwater habitats, as well as for ultra-short baseline navigation of autonomous vehicles.  Furthermore, this micro-transponder should remain unobtrusive to the natural activities of the subject because of its size and the frequency band in which it operates.