The ocean medium is probed with an acoustic pulse signal having a freq
uency bandwidth Delta f=70 Hz and a pulse duration tau=40 s over a sta
tionary acoustic range of 13.8 km in a shallow sea; the duration of th
e experiment is 1.75 h. The response function of the medium is observe
d to undergo only slight fluctuations, preserving its basic structure
throughout the entire experiment. The fluctuations of the signal trans
it time do not exceed a few milliseconds.