Geco A.s.

Cato Bjelland

Jan-Age Langeland

Seismic streamers (detection cables) used in the reception of reflection signals during seismic surveys at sea, where the streamer is towed behind a vessel, are constructed with an external, tubular cover (1) of a flexible plastic material. In order to reduce the noise produced by movement of the streamer through the water the external cover (1) is constructed with continuous longitudinally extending grooves (3) in its longitudinal direction, and preferably regularly disposed circumferentially around the entire periphery of the cover (1).

Device for use in a seismic streamer

A method for calibration of hydrophone groups is based on the use of a Helmholtz resonator, which is arranged such that a seismic streamer (Il) or sections thereof can be placed in the resonator's cavity (1) and connected via a hydrophone group selector (9) to a signal analyzer (6). A sound source (3) provided in the Helmholtz resonator is driven by a white noise signal at a frequency close to the resonator's resonance frequency. The sensitivity of the hydrophones in the respective hydrophone group (10) which is to be calibrated is determined by passing the hydrophone signals to the signal analyzer (6) where they are compared with a reference signal from a reference transducer (5), e.g., a measuring microphone, provided in the resonator. The Helmholtz resonator is designed as a drum-shaped vessel (1) provided with a funnel-shaped neck which constitutes an acoustic horn (2) and creates an impedance matching between the vessel (1), which constitutes a resonant cavity, and an electrodynamic transducer, which constitutes the sound source (3), provided at the smaller end of the horn (2). For the measurements a measuring microphone (5) is provided inside the cavity together with, e.g., a reel (4) or drum on which are wound sections of a seismic streamer, or a seismic streamer (11), whose hydrophone groups (10) are to be calibrated.

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Isdalsto, Norway

Cato Bjelland