Development and tests of SONAR array for underwater communication

Abstract: Water covers about 70 % of Earth’s surface. Most of the water is located in the ocean’s, which have an average depth of almost 3700 meters. This implies that there is a multitude of phenomena to investigate and discover. But due to human limitations other methods and tools need to be considered in order to investigate the depths. With help of underwater robotics it can be possible to reach further and deeper. In Sweden a research center named SMaRC (Swedish Maritime Robotics Centre) was established. Mainly to maintain the knowledge Sweden posses in underwater technology. The goal is to develop the next generation robots which are smarter, offers longer reach and higher endurance. Currently one of the projects at SMaRC is dealing with underwater communication, where a five element SONAR array has been developed.This thesis deals with characterising the five element SONAR array developed in SMaRC. This is done using two different methods, one theoretical and one experimental. The theoretical method involves modelling the directivity and beam steering the SONAR array has, using theoretical formulas. While the experimental method involves a field test where the directivity and beam steering is measured and analyzed. These two methods are then compared with each other and the result is analyzed.Both the methods are showing similar results for the directivity, where the main lobe is located at 0°. Beam steering of 45° and 60° also gives similar results. For a steering of 45° the main lobe is closer to the input angle in the theoretical method than in the experimental method. In beam steering of 60° the locations of the main lobes are shifted and the experimental method lies closer to the input angle. The side lobes also differs slightly between these two methods and no explanation was found. The Source Level (SL) for different beam steering are recorded in the experimental method to: Phase of 0° gives a SL of 131 dB re. μPA/V at 1 m Phase of 45° gives a SL of 129 dB re. μPA/V at 1 m Phase of 60° gives a SL of 128 dB re. μPA/V at 1 m