The influence of array vertical directivity patterns on bottom reverberation for mid to high frequency active sonar working in littoral shallow waters

Bottom reverberation is usually the main limitation for mid-to-high frequency active sonar working in littoral shallow waters to detect slow moving underwater small objects. Signals from the vertical side lobe of sonar array are usually at relatively large grazing angles when they reach the bottom, and the bottom backscatter strength is much larger at these grazing angles than that at small angles at which the signals from vertical main lobe reach the bottom. In some cases (especially when the seabed is acoustically hard), even though there is reflection loss and the amplitude of the side lobe signal is much lower than that of the main lobe signal, the reverberation caused by the side lobe signal is still more important. Quantitatively analysis on this subject is given in this paper by choosing two rectangular plane arrays with vertical beam-width θ_-3dB = 3° and θ_-3dB = 10° as projectors, and 40m as water depth.