VRAP (Radio Acoustic Positioning) System

VEMCO’s VRAP system measures real-time, detailed position information from underwater acoustic transmitters using a series of three buoys and a two-way radio link to a base station. Depending on environmental conditions, the VRAP system is typically able to furnish position information with a resolution in the range of 1 to 2 meters within the buoy triangle. Scientists use the VRAP system to investigate a wide range of animal species from lobsters to sharks. Applications include ecological impact studies, bioenergetics, spawning aggregate interactions, predator versus prey interactions and site residency studies. VRAP is particularly useful in studying the impact of various environmental conditions such as changing tides, sea state, temperature and storms on the movements of aquatic organisms.

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.

Software Features:

VEMCO’s VRAP5 software was developed to give users detailed position information on tagged animals within the buoy triangle. Features and capabilities of the software include:

• The ability to concatenate separate studies. For example, if it is necessary to move the buoys mid-study or temporarily suspend data acquisition, the software can connect and re-play separate segments as a continuous study.
• Tag data can be visually removed from the screen at any point during a study and the data is still be recorded.
• Calibrates buoys using a true speed of sound for that specific operating environment.
• Adds time referenced notes during a study. For example, for data analysis, it may be helpful to note that a noisy vessel entered the study area, or the wind direction changed.
• The ability to specify the period of time the system tracks an individual tag and the frequency of the data upload. For example, a researcher may have three tags in the water. You may want tag number 1 tracked for five minutes at a time, and tags 2 and 3 tracked for one minute each. The data upload period can also be specified for each tag.  For instance, position updates from tag number 1 can be sent to the base station every ten seconds whereas the other two can be uploaded every 30 seconds.
• Tracks two-channel telemetry tags. The new system will position a transmitter that senses both depth and temperature. [V16P, V16T, and V16TP].
• Adds “way points” to a study. Users can add “reference points” on a screen.
• Provides a buoy status window with information on signal strength, battery voltage, receiver gain, time of last communication and tag status.

VRAP software gives users the ability to process the true latitude and longitude position of tags. Users with latitude & longitude data on a scaled bitmap can determine a true world position for the tagged animal based on buoy position.

Shown in the buoy triangle in red and green coloured lines are the travel patterns for two tagged lobsters. The location of dens and food foraging patterns can be identified.

Other VRAP features:

• The system automatically calibrates itself to quickly determine buoy-to-buoy separation distance upon startup or periodically by a user-programmed command. Necessity of re-calibration is highly dependent on environmental conditions. For example, during a very calm day, the self-calibration command may only need to be issued every few hours, whereas in heavy sea states, it may need to be issued every 30 minutes.
• Powerful 34 kHz calibration transmitters are built into the hydrophone.
• The VRAP system can receive any of VEMCO’s continuous transmitters. VRAP hydrophones are 50 to 80 kHz.
• By using special software (VR20RAD), buoys can be used individually to determine the presence or absence of a particular transmitter (triangulated position is not available) or depth or temperature data.
• VRAP has been used with other VEMCO equipment, such as the VR60 real-time receiver, to track an animal that travels outside the buoy area.
• If standard acoustic pingers are used for tracking, VRAP software will calculate the x and y position of the transmitter.  If 3D data is required, the z coordinate can be determined in one of two ways: use of a depth transmitter, or if the animal being studied travels at a reasonably constant depth, its depth can be manually entered in the system (this will be an estimate only).
• The user can add "reference" pingers set at fixed points near the sea floor within the buoy triangle. This allows for evaluation of buoy movements during tidal movements or rougher sea states.

Specifications: