Cours sur les méthodes d'évaluation acoustique ... - Fao - Copemed

Simrad EK 500 / EY 500Reference target.Simrad supplies copper spheres designed as reference targets for thecalibration of scientific sounders. Copper is selected because it is a metalwhich can be made electrolytically with high purity. The spheres aremachined to the perfect spherical form with great accuracy, and a nylon loopis attached. Except for 12 kHz, 49 kHz and 50 kHz, the sphere diameter isdifferent for each frequency in order to obtain a target strength with minimumdependence of temperature (K. Foote 1983). A curve showing the variation ofthe target strength follows each sphere. The curve for the 38 kHz sphere isshown below as an illustration.Simrad copper spheresFrequencykHz12*18273849*50*70120200710* same sphereDiameter mm speed 1490 m/s dB45.063.042.060.045.045.032.123.013.710.3-40.4-34.4-37.9-33.6-36.4-36.2-39.1-40.4-45.0-50.5TARGET STRENGTH (dB)-34.5 -34.0 -33.5 -33.060 mm COPPER SPHERE38 kHz3.00.31400 1420 1440 1460 1480 1500 1520 1540 1560SOUND SPEED (m/s)(CD3146)msSIMRADoct.1991PULSE DURATIONFigure 2 Target strength of a 60 mm copper sphere.P2260/E 7