Angular dependence of Bloch wavepackets.

The contribution to an echo by a particular scattering mechanism, which occupies a specific region in the time‐frequency or time‐scale domains, is defined as a wavepacket [N. Yen, J. Acoust. Soc. Am. 81, 1841–1850 (1987)]. Previous studies have isolated wavepackets generated by specular reflection, Bragg reflection and Bloch waves in backscattered echoes from a ribbed, finite cylinder at a few discrete target aspect angles. For this target, the echoes mainly contain components from specular reflection and Bloch waves in the frequency region near ka≂5. These two kinds of wavepackets are experimentally extracted in the time‐scale domain over the angular range from 10° to 70°. The time extents and spectra of these wavepackets are shown to vary with target aspect angle. This angular dependence is shown to be related to physical mechanisms. [Work supported by NRL 6.2 funds.]