Seismic Integrated Positioning System 2
From Acoustic Positioning
Deep marine seismic operations involve vessels towing long, wide hydrophone arrays. The challenge this presents is to maintain positioning accuracy in the acoustically hostile conditions created by the ship’s wake and deafening noise from the seismic airguns and for the acoustic equipment to survive in the high shock environments. Sonardyne’s second generation Seismic Integrated Positioning System (SIPS 2) meets these challenges through a combination of digital and tone acoustic ranging techniques to provide full streamer acoustic positioning on the largest of spreads.
Full Streamer Acoustics
SIPS 2 is Sonardyne’s market-leading seismic source and streamer acoustic positioning system designed to meet the operational requirements of deep marine survey vessels towing long, dense arrays.
Acoustic transceivers attached to each streamer, air gun and tailbuoy/ navbuoy measure ranges between each other and the survey vessel. This enables both the shape of the towed array to be known and the position of the hydrophones, relative to the vessel to be precisely determined.
SIPS 2 is capable of handling small or large towed arrays with a high immunity to noise and bottom bounce. The Digital Signal Processing architecture used by the system offers precise range measurement resolution and allows hundreds of acoustic ranges to be collected and processed in a single shot point.
Vessels operating with SIPS 2 have demonstrated their ability to maintain performance when weather conditions become marginal due to the robustness of the digital acoustic technology. An additional analogue ‘tone-burst’ modulation mode ensures reliable operation in the harshest of acoustic environments, as created by ship’s wakes and gun arrays.
A typical SIPS 2 system comprises of acoustic positioning transceivers attached to each streamer, source and tailbuoy, through-hull transducer, an onboard transceiver controller rack and a dedicated navigation computer running the SIPS 2 software.
XSRS’ are streamer-mounted transceivers that measure acoustic ranges to adjacent XSRS’. The units are battery powered and are constructed using a carbon composite housing. This offers superior corrosion resistance, even in extreme conditions, and a low in water weight, reducing the need for floatation near the device.
XSRS units are attached to the streamer using industry standard collars and typically spaced at 100 metre intervals within the front, middle and tail sections of the array. A typical 6 x 8 kilometre long streamer spread, for example, will require 42 XSRS unitsto derive a position solution with range redundancy. When full acoustic bracing of the network is required, transceivers can be placed down the entire length of the streamer.
Each XSRS has 4 receive channels and 1 transmit channel allowing simultaneous ranging between transceivers and the capability to receive 4 of 60 unique digital signals. Range data is transmitted to the vessel via the inductive coils contained within each streamer.
XSRS’ use standard ‘D’ size alkaline or long life lithium cells depending on the duration of the deployment required.
Sound Velocity Option
XSRS transceivers can be supplied with a direct reading sound speed sensor. This ‘time of flight’ sensor provides superior accuracy and ease of use compared to traditional CTD methods, particularly in areas affected by fresh water and salt water mixing.
The Head and Gun Positioning System (HGPS) comprises of shock-mounted acoustic transceivers designed to position the seismic sources and tailbuoys. The units are able to withstand the hostile environment around airguns and can be supplied with different transducer arrangements to accommodate an operator’s preferred deployment method.
Where it is not possible to run a communications and power cable between an HGPS and its vessel-based controller, a Radio Telemetry System (RTS) is available. This utilises a ruggedised marine radio in a splashproof enclosure to telemeter range data to the survey vessel.
The Controller Rack is a 19” rack mounted unit that provides the interface between the in-water acoustic devices and the user’s PC. As the slots of the rack are not designated for a particular board type, it can accommodate a total of 6 Controller Cards of any combination (XSRS or HGPS).
Each XSRS Controller Card can support up to 4 streamers with a maximum of 30 XSRS transceivers per streamer. Each HGPS/RTS Controller Card can communicate and provide power to 8 transceivers.
Computer and Software
The Navigation Computer is a purpose-built PC that is interfaced to the SIPS Controller Rack via a serial communications link. It is responsible for processing the raw range data collected by the Controller Rack and passing it to a client’s main navigation computer so that an absolute network solution may be obtained. The unit has been specifically designed to run Sonardyne’s family of software applications and features front-mounted USB ports for when access to the rear of the unit is restricted by rack mounting. A rack-mountable monitor and USB keyboard with integral touchpad is supplied as standard.
Standard software features include XSRS transceiver and HGPS communication tools and acoustic signal diagnostics. These help minimise job setup time and enable rapid
QC checks to be made. It also means the acoustic positioning system can be optimised to the survey vessel and its particular operating environment whether in deep water or shallow.
To improve the efficiency of streamer deployment and recovery operations, SIPS 2 can be integrated with Sonardyne’s automated asset tracking system – SATS. SATS uses the Radio Frequency Identification (RFID) tags already found in many seismic streamers to automatically record the serial number of each section as it passes onto and off the vessel.
As complete vessel fleets and also on-shore repair and storage facilities become equipped with RFID technology, it will become possible to achieve even greater use of streamer sections and associated equipment through improved knowledge of their whereabouts at all times.
The RFID equipment is installed on the fairleads that handle the streamers as they are deployed over the stern of the vessel. The small, completely non-intrusive RFID antennas have been specifically designed so that they can be built directly into the fairlead. As each tag, fitted into the two end terminations of each separate streamer section, passes through the fairlead, the antenna energises the tag causing it to respond with the unique serial number of the section.
The serial numbers are then recorded in a database and associated with other relevant information such as position, time, manufacturer and condition status. In addition to asset tracking of streamer sections, any other in-water device can be tagged including acoustic positioning devices, depth birds, canisters and floats.
- Scalable system for both small and large arrays
- Positioning capacity for up to 20 long, wide streamers
- Accurate positioning down the entire length of each streamer
- Proven performance and reliability
- Multiple signal modulation modes to suit operating conditions
- High immunity to bottom and surface bounce
- Long equipment battery life
- Full integration with automated asset tracking system
Positioning Capacity : 20+ Streamers
Acoustic Coverage : Partial or Full Streamer
Operating Frequency : Sonardyne EHF (55-110kHz)
Acoustic Range Resolution : 5mm @ 1500m/s Vp
System Sync Resolution : 75mm @ 1500m/s Vp
Typical Cycle Time : 600 ranges in 7 seconds
Immunity to Multipath : System can resolve bottom/ surface bounce greater
Data Output Format : Raw range data (Various industry standard formats)