A method is described for measuring the amplitude-frequency and spatial (directional) characteristics of underwater acoustic arrays in real environments, i.e., in the presence of interfering reflections. The method is based on the application of time-delay spectrometry and wideband swept-frequency signals. The results of fullscale experiments are reported, demonstrating the high accuracy, noise immunity, and efficiency of the proposed method.The measurement of the amplitude-frequency response (AFR) characteristics of underwater acoustic arrays in real environments poses a very complex problem. The influence of sound rays reflected from the surface of the water, wall surfaces, the bottom, suspension elements, etc., must be eliminated. Equally important is the assurance of adequate noise immunity so that accurate measurements can be performed in any water region independently of weather conditions.The tone-burst (TB) method is traditionally used for these tasks. However, the measurement accuracy at low frequencies is diminished by the influence of reflecting surfaces. It is generally inappropriate to consider such a thing as noise immunity in relation to the TB method, because the "complexity" (bandwidth-duration product) of the test signal is equal to unity. A measurement technique based on the use of a swept-frequency signal and processing of the signal by time-delay spectrometry (TDS) has been proposed [1] as an alternative. The TDS method has significant advantages not only over the TB method, but also over methods utilizing wideband signals (e.g., a pseudorandom pulse train) with correlation processing. These advantages are summarized as follows:1. The TDS method ensures good arrival-time separation of rays and, as a result, high measurement accuracy near the surface of the water and other reflecting or scattering objects.2. The bandwidth-duration product of the transmitted swept-frequency signals can attain tens of thousands, providing a 40-60 dB or even better improvement in the signal-to-noise ratio (SNR) in comparison with the TB method; the greater dynamic range (more than 80 dB) substantially expands the measurement capabilities and increases the accuracy of the measurements.3. The main signal processing is instrumental (hardware-implemented), permitting measurements to be performed in many channels simultaneously with the use of medium-capacity computers and input equipment.4. The method gives the complete (detailed) AFR over the entire frequency range of the signal after the processing of a single transmission of the sensing signal.5. Modem spectral-analytic methods are capable of improving the accuracy of transit-time measurements a hundredfold over correlation methods, making it possible to monitor the relative positions of elements of the measurement system in the course of the measurements.6. The deterministic and monotonic character of the time variation of the frequency are conducive, first, to "running" (no downtime) measurement of the angular (directional) dependence of the AFR of an array duri...

A new method of measuring the transit time of acoustic signals is discussed; it is based on the use of wideband swept-frequency signals and exhibits high accuracy, noise immunity, and simple hardware implementation. The accuracy of the results can be increased several orders of magnitude according to a narrowband deconvolution procedure developed by the authors. The gain can be close to the channel signal-to-noise ratio, as is indeed confirmed by the results of numerical calculations and full-scale experiments.

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