Towards a Redefinition of the National Geodetic Vertical Datum by the Integrated Geodesy Adjustment- A Viewpoint

Determination of Mean Sea Level (MSL) as a vertical datum for orthometric heights is a vital requirement for the readjustment of the National Geodetic Levelling Network. The vertical datum is defined to be the geoid whereby it's practical realization was brought by tide gauge obervations at very few selected points e.g. ports. Geodetic levelling observation could use these tide gauges as fixed points. Unfortunately, the so-called determined MSL differs significantly from the geoid due to local phenomena, such as sea surface topography, ocean currents, tides, etc. The solution leads to distortion in the levelling network or other height information. Using integration approach of the Global Positioning System (GPS) data connected between tide gauges, satellite altimetry data on sea near the tide gauges, derived potential differences (from levelling nets and gravity observations), gravity anomalies and the deflection of the vertical surrounding the tide gauges, the required reference surface could be precisely determined. From geodetic point of view, these data contribute to the vertical datum problem and is briefly presented in this paper by the expression of the associated parameters of the Integrated Geodesy Adjusment's Concept.