The aim of this Comment is to show that, when the normal velocity of the transducer is no longer constant, the algorithm that has been recently proposed by Wu et al. [J. Acoust. Soc. Am.99, 1339–1348 for Part I and 1349–1359 for Part II (1996)] cannot eliminate aliasing nor remove the phase error in the angular spectrum. In fact, in recent articles, Wu et al. proposed and used a new numerical algorithm for eliminating the aliasing in the spectrum. Moreover, they have shown that the phase error can be easily removed. In their investigation they used a planar transducer and linear array. To show the effectiveness of their algorithm, the normal velocity of the planar transducer or of the elementary transducers (in the case of the array) has been supposed constant.