KALIBRERING AV SEISMISK KABEL I EN HELMHOLZRESONATOR

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.