The need for detailed knowledge of conditions at the interface of the free stream at the mouth of a cavity resonator has led to the development of a computer‐assisted technique for velocity profile measurement. Basically, hot wire data are recorded simultaneously with sound pressure microphone data so as to permit later sorting out: of local velocity readings as a function of phase in the acoustic cycle. From the ensemble of stored surveys, turbulent velocity fluctuations can be averaged out and the time sequence of oscillating profile configurations can be reconstructed. By subtracting the mean profile from each element of the sequence, the profile of the underlying instability wave is exposed. Another use of the results is the determination of the fluctuating component of volume flow into the cavity by numerical integration. [Sponsored by Naval Ship Systems Command under a GHR contract administered by NSRDC]