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A candidate pair of standard targets for calibrating a scientific echo sounder over the frequency band 80–130 kHz

The potential design of a new scientific echo sounder, with nominal operating frequency band 80-130 kHz, raises the question of its calibration. It is proposed that this be done by the standard-target method. Based on an earlier study, which optimized a pair of solid elastic spheres for a broadband multibeam sonar with operating frequency band 70-120 kHz [Digital Object Identifier: 10.1109/OCEANS.2006.306944], a new target pair is specified by scaling considerations. Using the respective center frequencies of the two bands, the diameters of the new standard spheres of tungsten carbide with 6% cobalt binder are roughly 19/21 of the previous diameters, 75 and 84 mm, hence 68 and 76 mm. The broadband target strengths of the two targets are computed over a range of environmental conditions, proving their robustness.