(Radio Acoustic Positioning) System VRAP
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- In detail
Receivers on the buoys collect transmitter data from an animal that is being tracked. This information is then dispatched by radio to a base station and a position is calculated and displayed in real-time. This information is also automatically stored on the computer for later play back. Depending on transmitter type, temperature and/or depth data can also be collected.
The VRAP system can track up to 12 continuous type transmitters on different frequencies. As of 2002, the VRAP system can also identify and position coded transitters. Depending on the coded type of the transmitter, this could mean identifying as many as 65 thousand pingers on one frequency.
When the VRAP system is initialized, the base station sends a radio command to each of the three buoys to determine "buoy-to-buoy" distances. Positioning is performed in sequence and each transmitter can be monitored from five to 60 seconds. Ten seconds of monitoring is a typical range. Following initialization, each transmitter is positioned based on arrival time of the acoustic ping to each buoy.
All valid transmitter detections are recorded. In order for a triangulated position to be calculated, all three buoys must register a signal from a transmitter.
Operation
Buoys are easily deployed from a small boat and have side and bottom mooring lugs. Weighing 43 kilograms, each buoy contains a hydrophone, ultrasonic receiver, two-way radio link, a microprocessor controller, and re-chargeable battery. The base station includes a two-way radio, timing circuitry and a PC serial data link. Gain control is automatic. The buoys are normally re-charged by removing the buoy from the water and using an AC charger. Battery life depends on buoy listening time and radio usage and is typically in the range of seven days.