Convergence Zone Width Analysis Based on Ray Cluster Theory and Its Application in the Array Depth Optimization of Active Sensors

The active sensor often uses the convergence zone mode to detect a distant target in the deep ocean. However, convergence zones are regions with limited widths that only appear at some discrete distances. Thus, widening the width by adjusting the transmitting array depth facilitates target observation and detection. Traversal search is an effective method for determining the optimal depth, but the heavy computation burden resulting from the calculation of the transmission losses at all source depths impedes its application. To solve the problem, a fast method based on ray cluster theory is proposed. Due to the coherent sound field structure in the deep ocean, several ray clusters with different departure angles radiate from the source, where ray clusters with small departure angles reverse in the water and form a convergence zone. When the source is set to a depth that only the first ray cluster inverts in water, the maximum width of the convergence zone is obtained. Based on this, an optimal transmitting array depth selection method utilizing the reversion condition of the first ray cluster is formulated. Simulation results show that the active sensor can achieve a large convergence zone width with real-time performance using the proposed method.