Public defence in geoinformatics, M.Sc. (Tech.) Timo Saari
During the last glacial period, Finland was covered with an ice sheet of 2.5 km in thickness. The enormous weight of the ice sheet depressed the Earth’s crust into the asthenosphere. As the ice sheet started to melt, roughly 11 000 years ago, the crust began to rebound upwards causing the phenomenon known as post-glacial rebound (land uplift), which still continues in the present day. The land uplift changes and distorts heights, coordinates as well as gravity values, which is why the national height system needs to be updated occasionally. Traditionally, the update has been done with a method known as precise levelling, which is very accurate but extremely slow, as nationwide levellings have taken approximately 30 years.
This dissertation studied the modern GNSS-based techniques that could replace precise levelling as the method for the next national height system of Finland. The heights related to precise levelling and GNSS are different: precise levelling refer to the physical Earth, whereas GNSS refer to a mathematical figure approximating the Earth’s form. Thus, GNSS techniques provide heights that are purely mathematical and therefore lacks a physical connection to the Earth – i.e., have no information on the direction of water flow. To tie the GNSS measurements to the surface of the Earth, we need a geoid (geoid model) that is the equipotential surface of the Earth’s gravity field, which in theory coincides with the sea surface at rest.
This dissertation's results will be used for producing the next national geoid model of Finland. Additionally, the knowledge obtained from the GNSS/geoid method will be beneficial for the decision making of the chosen method for the next national height system of Finland.
Opponent: Professor Georgios Vergos, Aristotle University of Thessaloniki, Greece
Custos: Assistant Professor Maaria Nordman, Aalto University School of Engineering, Department of Built Environment
Contact information of the doctoral student: Timo Saari, [email protected], +358 50 357 4315
The public defence will be organised on campus (auditorium M1, Otakaari 1). Also online via Zoom; https://aalto.zoom.us/j/65963026500
The thesis is publicly displayed 10 days before the defence in the publication archive Aaltodoc of Aalto University.