Summation of modes of a sound signal in a shallow sea

Results of an experiment on the summation of selected modes of a sound signal in a shallow sea (the Barents Sea, a sea depth of 120 m, a 17-km-long path) are presented. The experiment is performed with the use of a point source generating a broadband pulsed signal with a duration of 5 s and a linear frequency modulation within 100–300 Hz. The mode selection in the in-sea experiment is achieved using a vertical antenna array (32 hydrophones, length of 96 m). It is shown that the mode signals selected at the end of the path are formed with a part of the path. The modes are summed coherently (with the use of two methods) and incoherently. The noise immunity of the mode summation is estimated.