Method for determining the position of seismic streamers in a reflection seismic measuring system

A method for determining the position of at least two seismic streamers, each having a fore end and an aft end, in a reflection seismic measurement system in 3-dimensional marine seismic surveys, wherein each seismic streamer is equipped with a plurality of compasses and comprises a plurality of active sections having known lengths inserted between a fore stretch section and an aft stretch section at each end, respectively, of the seismic streamers, said active sections being equipped with a plurality of hydrophones or hydrophone groups having known locations, wherein the fore stretch section is connected with a towing arrangement attached to a towing vessel and the end of the aft stretch section is provided with a tailbuoy having equipment for determining the position of the tailbuoy and an acoustic transceiver, and the measurement system further includes at least one seismic source provided with an acoustic transceiver and at least one towing vessel each equipped with an onboard computer system for positioning and navigational purposes and at least one acoustic transceiver, the method comprising:

• towing a float by at least one vessel;
• locating said float off and between the fore ends of said seismic streamers;
• providing said float with position determining means and an acoustic transceiver;
• disposing a plurality of acoustic transceivers at specific locations in each stretch section;
• providing further acoustic transceivers at certain locations in at least one of said active sections adjacent to a stretch section, so that said seismic streamers, vessels and seismic sources constitute a 3-dimensional structure;
• connecting said seismic streamers, seismic sources and floats with said at least one vessel in an arrangement forming at least one triangle network;
• providing at least one reference position at the at least one vessel position and at least one reference position at the position of at least one of the float and a tailbuoy;
• determining the position of the streamers by trilateration between the acoustic transceivers and the at least two reference positions, said trilateration comprising an acoustic distance measuring method producing hydroacoustic signals between the transceivers and determining the mutual distances between the acoustic transceivers by measuring the transit time of the hydroacoustic signals therebetween;
• evaluating the thus determined reference positions and distances in the at least one triangle network in a first step, and evaluating in a second step the position of said seismic streamers and the position of every hydrophone or group of hydrophones in the seismic streamers;
• and
• implementing said first and second steps as calculation procedures in said onboard computer system.