All people interested are very welcome!
From physics to geometry: a tapestry of heights
Generally speaking, Geodesy deals with both geometric aspects (size and shape of the Earth) and physical aspects (Earth’s gravity field). Nonetheless, it is very common to view them, geometry and physics, independently. This view is somehow inherited from the past, when horizontal networks were disconnected from vertical ones.
The focus of this presentation is with a quantity that is both geometrical and physical: heights. It will be shown that height, as geometric quantity, depends on physical parameters for its realization, being related to mass distribution (gravity) or components of the atmosphere (total electron content, temperature, pressure and relative humidity). In the context of “system of heights” we will present the rigorous orthometric heights, which, unlike Helmert’s definition, account for density variation, and discuss its relation with normal heights. We will then talk about the height determined with GNSS, the geodetic height, and its dependency on the proper knowledge of the neutral atmosphere. We will discourse about different ways of modelling the neutral-atmospheric delay using our efforts at UNB (UNB3 and VMF1) as examples. We will then talk about the inversion problem of obtaining water vapour and its potential use as geodetic constraint to climate models. The presentation will end with the interrelation between orthometric and geodetic heights, highlighting the Stokes-Helmert method.