ETALONNAGE DE FLUTES SISMIQUES DANS UN RESONATEUR DE HELMHOLZ

Le résonateur de Helmholz est conçu sous forme de récipient en forme de tambour (1), pourvu d'un col en forme d'entonnoir, qui constitue un cornet acoustique (2) et crée une adaptation d'impédance entre le récipient (1), qui constitue une cavité de résonance, et un transducteur électrodynamique, qui constitue la source sonore (3), prévue à l'extrémité du cornet (2). Pour effectuer les mesures, un microphone de mesure (5) est prévu à l'intérieur de la cavité, conjointement avec, par exemple une bobine (4) ou un tambour sur lequel sont enroulées des sections de flûte sismique ou une flûte sismique (11), dont les groupes d'hydrophones (11) doivent être étalonnés. 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.