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Author:Kuokkanen, Jaakko Akseli
Title:Ensimmäisen luokan painovoimaverkon tukimittaukset
Auxiliary measurements of the first order gravity net of Finland
Publication type:Master's thesis
Publication year:2012
Pages:ix + 57 + [10]      Language:   fin
Department/School:Maankäyttötieteiden laitos
Main subject:Geodesia   (Maa-6)
Supervisor:Vermeer, Martin
Instructor:Virtanen, Heikki
OEVS:
Electronic archive copy is available via Aalto Thesis Database.
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Location:P1 Ark Aalto  480   | Archive
Keywords:gravity net
gravity gradient
close mass anomaly
height
painovoimaverkko
painovoimagradientti
lähimassa-anomalia
korkeus
Abstract (eng): This 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.
Abstract (fin): Tämä työ käsittelee Suomen ensimmäisen luokan painovoimaverkon (FOGN, First Order Gravity Net) uudelleenmittauksen tukimittauksia.
FOGN:n keskeisin tarkoitus on tuottaa Suomen alueelle helposti saatavissa olevat, absoluuttiset painovoima-arvot relatiivisia painovoimamittauksia varten.
Säilyvyyden ja saatavuuden vaatimusten takia, FOGN-pisteet sijaitsevat yleensä kirkkojen portailla.

FOGN-pisteille määritettiin painovoima-arvot kenttäkäyttöön soveltuvalla A10-020 -absoluuttigravimetrillä vuosien 2009 ja 2010 aikana.
A10-mittauksista erilliset tukimittausryhmät määrittivät FOGN-pisteille koordinaatit, vaaitsivat korkeudet ja mittasivat relatiivigravimetrialla kolmitasoisen, vertikaalisen painovoimagradientin.
Vertikaalisen painovoimagradientin tarkoitus on johtaa absoluuttinen painovoima-arvo A10:n referenssikorkeudelta kaikille käyttäjän kannalta merkittäville korkeuksille FOGN-pisteen vertikaalilla.

Diplomityön aineistona olivat tukimittausten havainnot.
Takymetri- GPS- ja vaaitushavainnot tuotettiin FOGN-pisteiden tasokoordinaateiksi ja korkeuksiksi laatuarviointeineen.
Relatiivipainovoimamittauksista valittiin neljä edustavaa pistettä, joiden painovoimaa korkeuden funktiona mallinnettiin toisen asteen polynomilla.
Lisäksi tutkittiin voiko lähianomaliamassojen vetovoiman mallintamisella parantaa mallinnettua painovoimaa ja selittääkö se painovoimagradientin epävakion osuuden.
Gradienttitarkastelun tarkoituksena on tuoda esiin huomioita ja näkökohtia lopullista FOGN-gradienttien mallinnusmenetelmän valintaa varten.

Kirkon portaiden rakenteen arviointi osoittautui hankalaksi tehtäväksi.
Rakenteesta oli vaikea saada ulkopuolista tietoa ja vaikka sitä saatiinkin, niin portaiden vetovoima ei aina selittänyt painovoimagradientin epävakioisuutta.
Painovoimaerojen kolme havaintokorkeutta oli valittu siten, että portaiden vetovoiman mallilla korjattu painovoiman funktio ei merkittävästi eronnut alkuperäisiin havaintoihin sovitetusta kuvaajasta, jolloin koko menetelmän käytön tarpeellisuus kyseenalaistuu.
ED:2012-04-27
INSSI record number: 44335
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