Experimental Assessment of Achievable Accuracy of GNSS-Derived Heights from Carrier Phase-Based Positioning Techniques for Ellipsoidally Referenced Hydrographic Surveys

Ellipsodially referenced survey (ERS) is considered as one of the challenging issues in the hydrographic surveys due to the fact that the bathymetric data collected by this technique can be readily transformed either to the geodetic or the chart datum by application of some geoscientific models, such as geoid, hydrodynamic and sea surface topographic model. GNSS (Global Navigation Satellite Systems) is a preferred technique to determine the ellipsoidal height of a vessel reference point (RP) because it provides cost-effective and unprecedentedly accurate positioning solutions. Especially, the GNSS-derived heights include heave and dynamic draft (e.g., settlement and squat) of a vessel, so as for the reduced bathymetric solutions to be potentially free from these corrections. Although over the last two decades, DGNSS (differential GNSS), the relative positioning technique based on the pseudo-range observables, has been widely adopted in the bathymetric surveys, it only provides limited accuracy of the vertical position (e.g., few meters). This technical barrier can be effectively overcome by adopting the so-called GNSS carrier phase (CPH)-based techniques, enhancing accuracy of the height solution up to few centimeters. From the positioning algorithm standpoint, the CPH-based techniques are categorized under absolute and relative positioning; the former corrects GNSS measurement errors by the global or regional models (e.g., IGS and CODE), the latter uses the so-called differencing technique to eliminate and minimize common error sources between two receivers. This study has focused on assessment of achievable accuracy of the ellipsoidal heights obtained from the CPH-based techniques with a view to their applications to hydrographic survey where project area is few tens to hundreds kilometers away from the shore. Some field trials have been designed and performed so as to collect GNSS observables on static and kinematic mode. In this presentation, details of these tests and processed results are discussed.