Originally designed in 1987 for shallow water sub-bottom profiling in the Canadian Arctic, the IKB-SEISTEC profiling system has developed over the intervening years as a proven, surface towed, sub-bottom seismic profiler suitable for collecting high-resolution profiles in water depths from 2 to over 200m.
The system comprises a 2.5 metre long catamaran, which can be operated at speeds from 0 - 4 knots. The catamaran supports the boomer source and receiver in a streamlined faring. Cable lengths up to 50 metres or longer can be accommodated and offset towing is often used to place the catamaran outside the track of the tow vessel.
The source incorporated into the catamaran is a reliable, wide band electrodynamic model B3 "Boomer" which produces a single positive pressure transient of up to 218 dB//1µPa @1m with very high repeatability.
The receiver is based on the line-in-cone concept and is physically placed as close as possible to the source so that targets closer than 2 metres can be mapped with little or no discernible near-field distortion. The available overall system bandwidth is sufficient to resolve layering to better than 25 cm without any digital processing.
The system is available with the fully featured SPA-3 analog signal conditioner and processor with support for both real time, gray scale recorders and for digital data acquisition systems. This signal processor can also be used with an optional ministreamer for better system performance and penetration in difficult terrain.
For precision surveying, the catamaran can be fitted with a GPS antennae (see below) or be closely coupled to the tow vessel. A motion compensation system is under development.
Acknowledgments, Geomega Ltd, Budapest, Hungary.
- Overall length 240 cm, width 72 cm , height 58 cm
- Weight in air including source and receiver but without cable bundle - 95 kg
- Source to receiver spacing (Centre - centre) 70 cm - fixed
- Tow Cables are normally 25 m in length - can be longer
- Tow speeds in range from 0 to 4 knots
- Can be towed coupled to small boat and offset up to 20 degrees.
Attributes of SEISTEC Catamaran Configuration
- Fixed transducer geometry - important for high resolution and shallow water conditions
- Close proximity between source and receiver - necessary for maintaining good spatial resolution in very shallow water depth (less than 2 m)
- Excellent sound and vibration isolation between source and receiver - a further requirement for shallow water and noisy environments
- Hydrophone line-in-cone configuration in enclosed in space, low water turbulance
- High Receiver high front-back sensitivity ratio
- Baffled boomer to minimize upward energy
- Both receiver and source have small near field limits (necessary for close targets to minimize image smear).
- The source signature has broad (base) band characteristics with great potential for sediment classification and water column target recognition.
- Platform suitable for mounting heave compensation sensors for motion compensation.
- Platform suitable for mounting GPS antennae for precision positioning.
- Fixed towing datum - sea level.
Third Party Requirements
- Boomer Power Unit, Geopulse, EG&G, Huntec
- Gray scale Recorders, EPC dry and thermal, Dowty thermal.
- Digital Acquisition System supporting internal and external keying.
Performance Specifications for targets from 1 - 200m
- Boomer basic pulse duration 100 - 180 µs.
- Spectral Content 700 Hz - 12 kHz at 500 J input energy and 5.6 kV excitation
- Total system impulse response (boomer, receiver, processor 300 µs.
- This represents a 22.0 cm resolution limit for merging layers.
- Bottom arrival-time resolution 20 µs (equivalent to 1.5 cm)
- Penetration (to typical reflectors) with line-in-cone receiver, extended with ministreamer.
- Soft mud - up to 150 m
- Compact silts - approximately 60 m
- Sands - approximately 20 m.
- Limitations - Shallow gas and bedrock close to the seabed.
Has been used in since 1987 for both research and commercial operations in water depths from 1 to 750 m
Presently thirteen systems are in operation worldwide and projects have been undertaken on the East, West and Arctic coasts of Canada, and the USA, the Great Lakes, the St. Lawrence estuary, Bahamas, Panama, Fiji, UK, France, Holland, Ireland, Hungary, Italy, Africa. Sri Lanka, Indonesia, Ethiopia and Korea.
The profiling system been used from large 60m research vessels, 6 metre inboards, small boats and zodiacs in rivers, canals, lakes, fjords, estuaries, open ocean and inshore regions.
1. Catamaran - Boomer Source (Third party boomer plate can be accommodated)
- Line-in-Cone receiver
- Dual preamplifier
2. Towing Bundle - Double screened Coaxial Cable with 7kV rating - for Boomer
- Receiver cable
- Stress cable
3. SPA-3 Analog signal processor
4. Optional ministreamer
(1) Shallow water, high resolution profile from Lake Balaton, Hungary, September 1999. Data collected at the 1999 summer school hosted by the Geophysics Department, Eotvos Lorand University. Digitally recorded data shooting at 25cm intervals.
Acknowledgements, Geomega Ltd, Budapest, Hungary.
(2) Deep Water Section, Saguenay Fjord,Québec, Canada 1997.
Water Depth 268m, analog grey scale record. Vertical scale 10m/division
Simpkin, P.G. , "The Boomer sound source as a tool for shallow water geophysical exploraqtion ". In Marine Geophysical Researchers, (2005) 26:pp 171-181. Springer.
Mosher,D.C., Simpkin, P.G. , "Status and Trends of Marine High-Resolution Seismic Reflection Profiling: Data Acquisition." Canadian Journal of Earth Sciences 1999. In Press.
Tóth, Tamás, Simpkin, P.G., Vida, R., Horváth, F. “Shallow Water Single and Multichannel Seismic Profiling in a Riverine Environment”. Special Issue of “The Leading Edge”. Society of Exploration Geophysicists. Nov. 1997.
Simpkin, P.G., and Angela Davis, “For Seismic profiling in very shallow water, a novel receiver” in Sea Technology, Vol. 34, No. 9, September 1993.