Development of radial layout underwater acoustic marker using forward scan sonar for AUV

In this paper, we propose a design of underwater acoustic marker (UAM) system and introduce recognition and position estimation methods of UAM. The marker consists of a combination of concrete blocks, and marker tracking process is divided into two stages: recognition and pose estimation. In order to recognize the proposed marker, image processing of the sonar image is performed to calculate the cross-distance ratio of all candidate blocks labeled. The pose of the recognized marker can be estimated using the orthogonal projection image considering the characteristics of the sonar image coordinate system. Based on the known size of the marker, the elevation angle between the orthogonal projection plane and the surface of the placed marker can be found, and the 3D position and orientation of the marker can be estimated. An example design of the marker was made, and the recognition experiments were carried out with FFS in the water tank. Experiments were conducted to verify the recognition rate and estimation accuracy of the proposed method.