Browsing by Author "Kuokkanen, Jaakko Akseli"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item Auxiliary measurements of the first order gravity net of Finland(2012) Kuokkanen, Jaakko Akseli; Virtanen, Heikki; Maankäyttötieteiden laitos; Insinööritieteiden korkeakoulu; School of Engineering; Vermeer, MartinThis master's thesis describes auxiliary measurements of the FOGN (First Order Gravity Net). The main purpose of the FOGN is to provide precise reference values of gravity for relative gravity measurements. 51 FOGN stations are spread evenly within Finland. Usually, they are located at church stairs, where they are easily accessible regardless of season or time of day etc. Gravity values of the net were measured by the A10-020 absolute gravimeter in 2009 and 2010. Auxiliary measurements were performed separately from the A10 measurements. Auxiliary measurements included coordinate determinations, levelling and three level vertical gravity gradients measurements for FOGN stations. The vertical gravity gradient is needed to refer the absolute gravity value to the sensor height of the FOGN user's relative gravimeter. In this thesis, observations of coordinates and levelling observations are used to coordinates and heights of FOGN stations with accuracy analyses. From the gravity gradient measurements were chosen four representative stations. Dependence of gravity on height at those stations was modelled by a second degree polynomial. Furthermore, nearby anomaly masses of church stairs and their gravity effects on gravity gradients were modelled. The purpose of stair models was to research how well they explain the non-constant part of the gravity gradient and whether it is possible to improve the gravity model by modelling the gravity effect of church stairs. The purpose of the gradient research is to state conclusions and aspects for the final FOGN gradient modelling. The structure of the stairs proved difficult to assess. External information about the structure was hard to find and even if the structure was certainly known, it did not always explain the non-constant part of the gravity gradient. Three observation levels of gravity difference observations were chosen thus, that the gravity model improved by a gravity effect of stairs did not differ notably from a second degree polynomial fitted to the original observations.Item N2000-korkeusjärjestelmä(2009) Kuokkanen, Jaakko Akseli; Vermeer, Martin; Insinööritieteiden ja arkkitehtuurin tiedekunta; Ahonen-Rainio, Paula
