Assessment of the Steering Precision of a Hydrographic USV along Sounding Profiles Using a High-Precision GNSS RTK Receiver Supported Autopilot

Abstract

Unmanned Surface Vehicles (USV) are increasingly used to perform numerous tasks connected with measurements in inland waters and seas. One of such target applications is hydrography, where traditional (manned) bathymetric measurements are increasingly often realized by unmanned surface vehicles. This pertains especially to restricted or hardly navigable waters, in which execution of hydrographic surveys with the use of USVs requires precise maneuvering. Bathymetric measurements should be realized in a way that makes it possible to determine the waterbody’s depth as precisely as possible, and this requires high-precision in navigating along planned sounding profiles. This paper presents research that aimed to determine the accuracy of unmanned surface vehicle steering in autonomous mode (with a Proportional-Integral-Derivative (PID) controller) along planned hydrographic profiles. During the measurements, a high-precision Global Navigation Satellite System (GNSS) Real Time Kinematic (RTK) positioning system based on a GNSS reference station network (positioning accuracy: 1–2 cm, p = 0.95) and a magnetic compass with the stability of course maintenance of 1°–3° Root Mean Square (RMS) were used. For the purpose of evaluating the accuracy of the vessel’s path following along sounding profiles, the cross track error (XTE) measure, i.e., the distance between an USV’s position and the hydrographic profile, calculated transversely to the course, was proposed. The tests were compared with earlier measurements taken by other unmanned surface vehicles, which followed the exact same profiles with the use of much simpler and low-cost multi-GNSS receiver (positioning accuracy: 2–2.5 m or better, p = 0.50), supported with a Fluxgate magnetic compass with a high course measurement accuracy of 0.3° (p = 0.50 at 30 m/s). The research has shown that despite the considerable difference in the positioning accuracy of both devices and incomparably different costs of both solutions, the authors proved that the use of the GNSS RTK positioning system, as opposed to a multi-GNSS system supported with a Fluxgate magnetic compass, influences the precision of USV following sounding profiles to an insignificant extent.

Development and Performance Measurement of an Affordable Unmanned Surface Vehicle (USV)

“…While from the prior study by Marchel, USV equipped High-Precision RTK Receiver and speed of 2.5 km or 1.3 m/s were acquired at 0.919 m for the average of CTE. It concludes that The effect of RTK Receiver for zigzag path-following is not considerably high compared to the performance of USV; this is in line with the conclusion that has been revealed [17].…”

“…Graph HDOP versus time when USV sailing is plotted in Figure 15. The conclusion drawn from the graph is the maximum HDOP value is 0.8, and the HDOP value vacillates between 0.6 and 0.8, which according to other studies, indicates high signal quality [17]. The final conclusion is that the accuracy value of a GPS is large because the HDOP value is below 1.5 and the number of satellites read by GPS is above 12 satellites.…”

“…M is defined as mass matrix, C(V) represents centripetal and Coriolis matrix, and D(V) is linear drag matrix. The effect of non-linear drag is ignored as the velocity is relatively slow [17]. Meanwhile, τ is input forces and moments generated by the thrusters.…”

“…Sutton et al conducted the adaptive non-linear control for the USV [15], and more sophisticated, robust control with Fuzzy Logic guidance is applied by Aguilar et al for improving the precision of USV maneuvering [16]. Marchel et al adopted a high precision Global Navigation Satellite System (GNSS) Real-Time Kinematic (RTK) to evaluate steering precision [17]. Even the Nonlinear Predictive Controller (NMPC) based on Convolutional Neural Network (CNN), and Ant Colony Optimizer (ACO) is proposed by Zhao et al from Wuhan University of Technology [18].…”

Analysis of GNSS, Hydroacoustic and Optoelectronic Data Integration Methods Used in Hydrography

“…Bathymetric surveys use devices and systems with different spatial reference systems, including the following [ 6 ] ( Figure 1 ): A positioning system is used to determine the coordinates of the vessel’s position. In hydrography, the most commonly applied positioning system is a Differential Global Positioning System (DGPS) or a Real Time Kinematic (RTK) receiver [ 7 ]. It determines the position coordinates that are presented in curvilinear coordinates (B, L, h) in relation to the reference ellipsoid used or in Cartesian coordinates (X, Y, Z); A sound velocity probe determines the sound velocity in water.…”