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This article provides an overview for HF beacon positioning.
The Type 7815 OBC Transponder has been designed for seismic Transition Zone (TZ) and Ocean Bottom Cable (OBC) applications, where large numbers of small, long-life Transponders are required to position the hydrophones or geophones along seismic lines.
The transponder has been specifically designed to meet the tough environment associated with deployment and recovery of shallow water seismic cables, and operates in the 25 kHz to 50 kHz High Frequency (HF) band.
They can be programmed and tested using a Type 7967 Test/Programming Box to any one of 401 interrogation Addresses, combined with any one of 9 Reply Channels – to provide 3609 unique identities.
Water depth is limited to 500m but typical slant ranges of 750 m – 1500 m are achievable (depending on vessel noise and seabed topography).
Beacons can be interrogated in one of two ways:
They can be interrogated from a single Remote Transducer (typically mounted to an over-the-side pole), through a Type 8263 HF Transceiver.
Simple range information is then collected from each beacon.
Alternatively, a USBL solution can be achieved by utilising Sonardyne’s Mini-Ranger 2 system, with an HPT 2000 MF Transceiver either fitted to an over-the-side, or through-hull-mounted pole.
Either type of data collection can be controlled by Sonardyne’s HydroPos survey control package.
Alternatively, 3rd party software can be used.
The range-only solution requires the vessel to sail past the beacon on both sides of the seismic line (in opposite directions), typically requiring a reasonably large number of position-fixes (about 40 minimum ideally) in each direction.
On the other hand, the USBL solution only requires a few good position fixes, the best quality ones typically when the vessel is directly above the beacon.
A common mistake by 3rd party programmers is to make the software Range Gate too large, so that too many beacons are trying to be tracked at once. As mentioned above, with USBL, you only need a handful of good replies to fix their position. If you have too many, then the long ranges to distant beacons may limit the number of good replies from nearby ones.
Contact Support@sonardyne.com for more information.
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