Sea Surface Heights Retrieval from Ship-Based Measurements Assisted by GNSS Signal Reflections

Abstract

Measurements of the sea surface height (SSH) can be carried out with GNSS aboard ships, but data about the static draft and the hydrodynamic squat effect are necessary. This information is often not available or has an insufficient accuracy. In this study, an alternative method based on the GNSS signal-to-noise ratio observations is presented. Using this method, the distance between the water surface and a GNSS antenna can be estimated directly, if corrections of the heave and the ship’s attitude are considered properly. Suitable segments of a 3-month dataset, gathered aboard a ferry ship operating in the German Bight, were analysed. A global optimization approach based on interval analysis was used and all available observations from a segment were analysed in a common adjustment calculation. The resulting SSH was validated with data from a tide gauge station at Heligoland. The mean difference is 4 mm and a standard deviation of the differences of 5.3 cm was found. The SSH for the same GNSS dataset was also derived from a well-established processing based on the comprehensive consideration of ship dynamics. The mean difference with respect to the tide gauge was 2 mm with a slightly smaller standard deviation of 4.0 cm.