Determination of the vertical directivity of a short pulse transmission at individual modes in a shallow sea

A method for the numerical determination of the directivity of an antenna array is considered with delay increments much shorter than the sampling period for the input signals. The method is used for determining the vertical directivity of individual modes specified according to their travel times at each hydrophone of the array. In addition to the signal with the directivity of the third mode, a signal is observed with the directivity of the first mode, which slightly advances the signal of the third mode but arrives noticeably later than the first-mode signal. The additional signal is received only by the hydrophones positioned near the sea bottom. This fact suggests a conclusion that the additional signal is caused by the scattering of the third mode from the bottom. The experiment is performed in the Barents Sea with a depth of 120 m at distances of 8 and 17 km.