Assessment of the Accuracies of Multibeam Calibration Values and the Depth between Real-Time Kinematics and Precise Point Positioning

Abstract Calibration of measurement equipment in the marine environment is critical in the attainment of expected accuracies. Multibeam device calibration is an important component of any hydrographic survey operations. The involves determining of the alignment angle between the multibeam sonar, motion sensor, and gyroscope, and accounts for the time delay (latency) between the sensors. Any errors in the positioning of the survey vessel will affect the multibeam calibration values and introduce systematic errors in the entire dataset. The main purpose of this work is to investigate the effects of horizontal and vertical positioning errors from two different GNSS positioning methods; Real-Time Kinematics (RTK) and Precise Point Positioning (PPP) methods, on the multibeam calibration values with varying depths. The approach involves the horizontal position of the pings as determined by integrating GNSS with inertial navigation systems using Kalman filtering techniques. The bathymetric depth determination is based on the ellipsoidal reference system using the EGM 2008 geoid model with a chart datum offset. The positioning and motion data were postprocessed to achieve the highest possible accuracy in the determination of the calibration parameters. The results show that the accuracy of the calibration value is a function of the positioning solutions. The RTK GNSS solution yields calibration value of \(-0.2{6}⁰± 0.02, 2.5{6}⁰± 0.14,\) and \(-1.4{4}⁰± 0.07,\) for the roll, pitch and heading respectively, with a standard error of \(2.514{cm/m}²\). The PPP GNSS solution gives a calibration value of\(-0.2{6}⁰± 0.02, 2.{67}⁰± 0.08,\) and \(-1.2{1}⁰± 0.13,\) for roll, pitch and heading respectively, with a standard deviation of \(3.203{cm/m}²\). The calibration values were used as systematic corrections in multibeam bathymetric surveys to improve the accuracy of the bathymetric data. The results show a deviation of 0.22m to 0.86m between the RTK derived bathymetric depth and the PPP derived bathymetric depth.