Expansion and improvement of the Israeli geoid model by shipborne GNSS measurements

The geoid is the equipotential surface that coincides with the sea level in the absence of such dynamic effects as tides, wind, ocean currents, and other disturbing forces. On land, geoid models are determined by using precise leveling, Global Navigation Satellite System (GNSS) measurements, and gravimetry measurements. However, in coastal areas, where performing precise leveling is not possible, geoid modeling relies solely on gravity measurements. Spaceborne gravimetry missions provide gravimetric measurements with global coverage. These measurements have low spatial resolution, which can reach distances of tens and hundreds of kilometers between tracks. Airborne and shipborne gravity measurements can be used to fill the gaps between tracks. In the absence of airborne and shipborne gravity measurements to densify the measuring data, shipborne GNSS measurements may provide a low-cost method for overcoming this problem in coastal areas. After applying several corrections to the raw GNSS measurements (accounting for systematic effects induced by ship dynamics and other static and dynamic impacts from tides, atmospheric pressure, or wind stress), approximate geoid height with fair accuracy could be extracted. An experiment was conducted along the Israeli coast, during which several GNSS surveys were carried out between the years 2011 and 2015. This paper illustrates the steps needed for the extraction of such heights and provides a comparison of the results between the Israeli official geoid model and the expanded one, complete with its quality assessment.