On the dynamics of physical heights and their use for the determination of accurate orthometric/normal heights

Physical heights, e.g. orthometric and normal heights, are, so far, practically considered as static heights in the majority of land areas over the world. They were traditionally determined without considering the dynamic processes of the Earth induced from temporal mass variations within the Earth’s system. The Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) satellite missions provided unique data that allow the estimation of temporal variations of geoid heights and vertical deformations of the Earth’s surface, and thereby the dynamics of physical heights. They revealed that for the large river basin of a strong hydrological signal (e.g. the Amazon river basin), peak to peak variations of orthometric/normal height changes reach 8 cm. The objective of this research is to discuss the need of considering the dynamics of physical heights for the determination of accurate orthometric/normal heights. An approach to determine the dynamics of physical heights using the release 6 (RL06) GRACE-based Global Geopotential Models (GGMs) as well as load Love numbers from the Preliminary Reference Earth Model (PREM) was proposed. Then, the dynamics of orthometric/normal heights was modelled and predicted using the seasonal decomposition (SD) method. The proposed approach was tested over the area of Poland. The main findings reveal that the dynamics of orthometric/normal heights over the area investigated reach the level of a couple of centimetres and can be modelled and predicted with a millimetre accuracy using the SD method. Accurate orthometric/normal heights can be obtained by combining modelled dynamics of orthometric/normal heights with static orthometric/normal heights referred to a specific reference epoch.

Keywords: dynamics of physical heights, GRACE, accurate orthometric/normal heights, temporal variations of geoid/quasigeoid heights, vertical deformations of the Earth’s surface