Sonardyne - Transition Zone and Ocean Bottom Cable Acoustic
From Acoustic Positioning
Designed to work with Transition Zone (TZ) and Ocean Bottom Cable (OBC) and seismic techniques, Sonardyne’s acoustic positioning system significantly improves the speed, accuracy and efficiency of positioning seabed marine seismic cables. The system uses a network of low cost, rugged transponders that can withstand fast deployment through mechanical ‘squirters’ to provide users with an efficient method of collecting the positions of thousands of seabed hydrophones in real-time and in water depths from 1 to 500 metres.
A typical system comprises of acoustic positioning transponders attached to the seismic cable, a vessel-based acoustic transceiver interfaced to a client’s PC running the Sonardyne HydroPos software application. Third party software applications which incorporate an acoustic control module can also be used with the system.
Prior to deployment from a cable lay boat, transponders are attached to the seismic cable at each ground station to be positioned. Once the cable is laid, the system precisely measures the acoustic range (distance) from a surface transceiver on the pinging vessel to each transponder to enable its exact position to be established. The positioning process is more accurate than traditional first break techniques, 1-2 metres absolute, and can either be conducted once the cable is laid or later whilst shooting.
The transponders developed for the system are small and lightweight and have been proven to be able to withstand the demanding and varied operational environment of surveys.
Standard features of the Type 7815 transponder include a depth rating of 500 metres, a unique acoustic ‘address’ enabling thousands of units to be laid in a single deployment and battery voltage monitoring to allow users to better plan their maintenance schedules.
In operations using a ‘squirter’ cable deployment system, carapaces are available that provide impact protection for the transponder. The carapaces are manufactured from
ABS plastic that encapsulates the transponder and optional RFID asset tracking tag, clamping it securely to the cable whilst protecting it from impact and pressure forces encountered during cable deployment and recovery.
The carapace design, which is now in use with many crews around the world, has been proven to be easy to fit and reduces long term maintenance when compared with traditional tie-wrap and tape methods. The low profile shape of the carapace also reduces the risk of snagging and is acoustically quiet in the water, creating less noise interference down the cable.
Lightweight Release Transponder
The Lightweight Release Transponder (LRT) offers the same acoustic positioning features of the Type 7815 but incorporates a unique ‘screw-off’ release mechanism to simplify equipment recovery. Furthermore, the LRT can be fitted with a bolt-on rope canister that provides a fast and efficient method of recovering seismic cable back onboard a vessel.
By mooring the LRT and rope canister to the end of the cable, then acoustically commanding it to ‘release’, the transponder returns to the surface under positive buoyancy, leaving one end of the rope still attached to the bottom cable. This can then be hauled onboard and the cable pulled up to the surface.
On command from a PC equipped with HydroPos control software, Sonardyne’s
Type 7911 OBC 12 acoustic transceiver interrogates the seabed transponders and simultaneously takes in DGPS information. This raw data is then pos-processed to produce ground station positions to better than 2 metres absolute. Data can also be output to the client’s own navigation processor for independent final network adjustment.
The transceiver comprises of a rugged waterproof electronics bottle connected to a remote acoustic transducer which is generally deployed on a pole over the side of a vessel, or permanently through the hull.
HydroPos V2 Software
HydroPos V2 is a multi-module software programme that allows the user to plan, acquire and post process TZ/OBC acoustic positioning data. The software is designed to run on a PC operating either Windows XP or Windows 7 with a recommended display resolution of 1024 x 768.
Line data can be imported in OGP P1 and SEG SPS formats as well as a CSV file and once loaded, transponder locations can be simply added either by ‘hand’ or via the HydroPos V2 RFiD Cable deployment modules.
During acoustic acquisition, HydroPos commands the OBC 12 transceiver to interrogate the relevant seabed transponders and logs their acoustic replies. An initial online positioning solution is available on the acquisition screen with a visual indication of positioning accuracy.
HydroPos also provides on-line vessel positioning information to the user, to enable acquisition by the most efficient sail line plan, and at the optimum interrogation speed and geometry as well as an independent helmsman’s display to provide vessel guidance. The helmsman’s display is available to all PCs on the same network as the acquisition PC.
On completion of data acquisition, the raw data can be exported from HydroPos into OGP P2/94 or SEG SPS format for submission to the client.
HydroPos is also able to post process the raw data. This simple procedure also allows the operator the ability to automatically or manually remove any ranges which obviously do not fit the solution. Data can be processed several times allowing for different parameters and scenarios to be tried; for example, alterations to sound speed, solving for depth or fixed depth and tidal corrections.
All raw and processed data is stored in a single, user-selectable, logging file (.LOG) to allow easy archiving of the data. The recorded .LOG file contains all the online acquisition parameters as a header, followed by blocks of recorded data. This enables the data to be easily processed as blocks of data, either at a later date, or at a remote location if required.
RFID Asset Tracking
In large surveys where hundreds of acoustic transponders are deployed, monitoring equipment movements can be time consuming and inaccurate. Sonardyne’s OBC RFID system automatically logs the identities of transponders and cables as they are deployed from vessels, together with their associated GPS drop co-ordinates.
The system comprises of four main parts; an RFID software module within HydroPos
V2, reader modules, antennas and small passive RF tags.
During cable deployment, as a transponder fitted with an RF tag passes antennas built into the chute, its address, channel and asset description is read and logged within HydroPos V2, along with current GPS location. Using the interfaced surface navigation data, HydroPos V2 then determines which Receiver Group the transponder is associated with and automatically includes this information with the line definition in the property cable file.
- Operating Depth Range : Operating Frequency : Sonardyne HF (35-55kHz)
- Acoustic Positioning Capacity : 3600 transponders in real time
- Positioning Accuracy : 1-2 metres absolute
- Transponder Battery : Life Up to 18 months (Alkaline battery)
- Required Operating System : Windows XP or Windows 7
- HydroPos V2 Data Import Format : OGP P1, SEG SPS, CSV
- HydroPos V2 Data Export Format : OGP P2/94