Abstract
<p class="Abstract">Differential GNSS positioning on vessels is of considerable interest in various fields of application as navigation aids, precision positioning for geophysical surveys or sampling purposes especially when high resolution bathymetric surveys are conducted. However ship positioning must be considered a kinematic survey with all the associated problems. The possibility of using high-precision differential GNSS receivers in navigation is of increasing interest, also due to the very recent availability of low-cost differential receivers that may soon replace classic navigation ones based on the less accurate point positioning technique. The availability of greater plano-altimetric accuracy, however, requires an increasingly better understanding of planimetric and altimetric reference systems. In particular, the results allow preliminary considerations on the congruence between terrestrial reference systems (which the GNSS survey can easily refer to) and marine reference systems (connected to National Tidegauge Network). In spite of the fluctuations due to the physiological continuous variation of the ship's attitude, GNSS plot faithfully followed the trend of the tidal variations and highlighted the shifts between GNSS plot and the tide gauges due to the different materialization of the relative reference systems.</p><p class="Abstract"><span lang="EN-US"><br /></span></p>
Highlights
The problem of calculating the connection between on-shore and off-shore heights is still very open and debated
[8] these are ideal conditions that are never found in nature, and for this reason the materialisation of altimetric reference systems at sea is profoundly different from terrestrial altimetric reference systems [9]
The variations measured by the tide gauges were compared only in terms of trend with the heights measured by the GNSS receiver on board the ship
Summary
The problem of calculating the connection between on-shore and off-shore heights is still very open and debated. The ground altimetric reference system is generally based on the definition of a specific equipotential surface of the gravitational field, identified by the mean level of a reference tide gauge. This method has been used in Italy both historically [2] and currently [3] and various national terrestrial altimetric systems have been defined, for this reason the possibility of unifying them at a regional [4] and global level [5] is currently subject of research. It is important to underline that the interest in this case is mainly in seafloor depth in order to construct high resolution digital elevation model (DEMs) for seafloor, habitat
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