Offnormal Incidence Reflection-Coefficient Determination for Thick UnderwaterAcoustic Panels Using a Generalized ONION Method

摘要

The ONION method is a reflection-coefficient measurement technique designed foruse on data acquired from thick underwater acoustic panels in the frequency range 1-10 kHz, but may be used to frequencies as high as 25 kHz. The method extrapolates transient reflected-wave data using least-squares fitting to a multiple-layer panel model. A description of the method, as it applies to data acquired using a normally incident interrogating wave, is provided in 'The ONION method: A reflection coefficient measurement technique for thick underwater acoustic panels'. The present article describes research directed toward generalizing the method to allow for an offnormal incidence interrogating wave. Successful applications of the generalized method to data acquired under offnormal incidence are described. The generalized method was applied to measurements that were made on two different sample panels. The measurements involved one test temperature, two hydrostatic test pressures, and three test frequencies. Keywords: Panel measurements; Reflection measurements; Least squares fitting; Signal extrapolation. Reprints. (JHD)