I. Introduction
Robotic surface vehicle (RSV) is a marine robot capable of accomplishing various tasks without human operations with available sensors onboard [1], [2], [3]. In order to accomplish various tasks autonomously, a reliable and high-performance motion control system is vital. The motion stability is vulnerable to unknown internal dynamics and external ocean disturbances due to wind, waves, ocean currents, and operational equipments [4]. In order to achieve high-performance control in the presence of the external disturbances and internal dynamics, a variety of effective methods are proposed, ranging from robust control [5], [6], adaptive control [7], intelligent control, disturbance-observer-based control [8], to active disturbance rejection control (ADRC) [9].