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Some recent developments will be mentioned here because the methods of hydrographic surveying that have been described necessarily are subject to change.
Height determination by means of GPS
The BSH is developing novel methods of tidal reduction for the North Sea. By determining the height of the transducer above the ellipsoid by means of DGPS, measurements are no longer influenced by sea states and water levels. Apart from technical details regarding the spatial and temporal relation between echsounder and GPS antenna, one major problem that remains to be solved is the distance between ellipsoid and chart datum at any point.
Change-over from Mean Low WaterSprings (MLWS) to Lowest Astronomical Tide (LAT)
 Additional data is available here.
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