4:45 PM - 5:00 PM
[G02-6-02] The permanent tide and the International Height Reference System IHRS
The IAG in its resolution No. 1 at the 26th General Assembly of the IUGG in Prague in 2015 adopted the mean-tide system for the International Height Reference System (IHRS). This was a partial reversal of earlier recommendations: IAG resolutions 9 and 16 at the XVIII General Assembly of the IUGG in Hamburg in 1983 had recommended the zero-tide system for handling the permanent tide in geodetic quantities.
In practice, the treatment of the permanent tide has been highly variable even after 1983. So is there anything new in the IHRS from this viewpoint? After all, we are well accustomed to mean-tide height systems at the national level. The reductions that are needed when we combine them with say 3-D positions in a conventional tide-free system and gravimetric geoid heights in the zero-tide system are also well-established.
However, there is a tidal novelty in the IHRS and that is its reference level. The national mean-tide height systems depended on a physically defined reference, usually traceable to the mean sea level at some tide gauge(s). The reference level of the IHRS is an equipotential surface where the geopotential has the conventional value W0=62636853.4 m^2/s^2. This value was first determined empirically to well approximate the global mean sea level and then adopted as a convention.
In which way does the W0 depend on the tidal system used, first in the determination, and then in the applications after the adoption as a convention? Or is there any dependence at all? This is the main subject of the presentation. I also provide a summary of reduction formulas between different tidal systems, consistent with the current IERS Conventions, and a compendium of older approximate formulas used in legacy geodetic systems.
In practice, the treatment of the permanent tide has been highly variable even after 1983. So is there anything new in the IHRS from this viewpoint? After all, we are well accustomed to mean-tide height systems at the national level. The reductions that are needed when we combine them with say 3-D positions in a conventional tide-free system and gravimetric geoid heights in the zero-tide system are also well-established.
However, there is a tidal novelty in the IHRS and that is its reference level. The national mean-tide height systems depended on a physically defined reference, usually traceable to the mean sea level at some tide gauge(s). The reference level of the IHRS is an equipotential surface where the geopotential has the conventional value W0=62636853.4 m^2/s^2. This value was first determined empirically to well approximate the global mean sea level and then adopted as a convention.
In which way does the W0 depend on the tidal system used, first in the determination, and then in the applications after the adoption as a convention? Or is there any dependence at all? This is the main subject of the presentation. I also provide a summary of reduction formulas between different tidal systems, consistent with the current IERS Conventions, and a compendium of older approximate formulas used in legacy geodetic systems.