ON THE MEASUREMENT OF SHOCK WAVES.

The class theoretical formulation of finite-amplitude distortion invariably depict continuous sinusoidal waves which develop into sawtooth or N-shaped waves. In practice, waveforms are observed with gross asymmetries between positive and negative pressure amplitudes, high-amplitude spikes, notches, ringing, and other peculiarities. Phenomena accounting for anomalous waveshapes are discussed. It is shown that linear mechanisms explain some major discrepencies between classic sawtooth waves and those typically recorded by PVDF (polyvinylidene difluoride) hydrophones corrected to an oscilloscope. The first is a relative phase shift between the fundamental and second (and higher) harmonics which occurs in a diffraction-limited focused field. The second class of linear mechanisms involves hydrophone cable and impedance mismatch effects which alter both time-domain and frequency-domain characteristics of the actual pressure waveform incident on the hydrophone. These effects and others are illustrated. The results form the basis for some recommendations on experimental procedures in nonlinear wave propagation.