Geoid and postglacial rebound related gravity change in Finland

Mirjam Bilker-Koivula

Geoid and postglacial rebound related gravity change in Finland

Julkaisun otsikon käännös: Geoidi ja maannousuun liittyvät painovoiman muutokset Suomessa

Mirjam Bilker-Koivula

Tutkimustuotos: Doctoral Thesis › Collection of Articles

Abstrakti

Satelliittipaikannus (GNSS) on nykyään laajasti käytössä ja sen tarkkuus paranee koko ajan. Tämä vaatii myös parempia geoidimalleja, joita tarvitaan kun satelliittipaikannuksella mitattuja korkeuksia muunnetaan kansallisessa korkeusjärjestelmässä oleviksi korkeuksiksi. Suomessa korkeudet muuttuvat jatkuvasti jääkauden jälkeisen maannousun johdosta. Maannousumalleja kehitetään Fennoskandian maannousualueelle, ei pelkästään koordinaattien pystykomponentin nopeuksille, vaan myös jääkauden jälkeisen maannousuun liittyville painovoimamuutoksille. Tässä väitöskirjassa tehtiin geoiditutkimuksia etsittäessä geoidimallia, joka parhaiten sopii muuntamaan EUREF-FIN koordinaattijärjestelmässä olevat GNSS-korkeudet Suomen N2000- korkeusjärjestelmässä oleviksi korkeuksiksi sekä maalla että merellä. Absoluuttipainovoima-mittauksien aikasarjoja analysoitiin painovoiman muutosnopeuksien ja pystysuuntaisten nopeuksien väliseen suhteen määrittämiseksi. Geoiditutkimuksessa testattiin menetelmiä, joilla geoidimalli sovitaan GNSS-vaaitus aineistoon. Parhaaksi menetelmäksi Suomessa osoittautui pienimmän neliösumman kollokaatio yhdessä ristivalidoinnin kanssa. Tulos oli FIN2005N00-korkeuden muunnospinta, josta tuli Suomen virallinen geoidimalli. Seuraavaksi testattiin korkean resoluution globaaleja painovoimakenttämalleja Suomen geoidilaskennassa. Tuloksena olevat geoidimallit olivat parempia kuin aiemmat geoidimallit Suomen alueelle. Vakioeron ja kallistuksen poistamisen jälkeen erot muihin malleihin hävisivät. Lisäksi kehitettiin menetelmä, jolla geoidimalleja voidaan tarkistaa merellä laivan GNSS-mittauksien avulla. Menetelmä onnistui ja tunnistettiin keskeiset elementit prosessille, jolla muunnetaan GNSS havainnot mittauskorkeudelta geoidipintaan. Absoluuttigravimetrityyppien välisiä vakioeroja etsittiin tutkimalla kansainvälisten vertailujen, kahdenvälisten vertailujen ja trendilaskennan tuloksia. Trendilaskennan tulokset paljastivat merkittäviä vakioeroja IMGC, GABL ja JILAg-5 laitteille: 31.4 ± 10.9 μGal, 32.6 ± 7.4 μGal ja 6.8 ± 0.8 μGal. 12 aseman absoluuttipainovoimamittauksien aikasarjat analysoitiin ja seitsemälle asemalle saatiin luotettavat trendit. Painovoiman muutosnopeuksien ja pystysuuntaisten nopeuksien väliselle suhteelle estimoidut suhdeluvut vaihtelivat 0.206 ± 0.017 ja -0.227 ± 0.024 μGal/mm välillä ja akselin leikkausarvot 0.248 ± 0.089 ja 0.335 ± 0.136 μGal/v välillä. Nämä arvot ovat suurempia kuin odotettiin aikaisempien tulosten perusteella. Geoiditutkimuksista saatu tieto hyödynnetään Suomen seuraavien geoidimallien ja korkeuden muunnospintojen määrittämisessä. Ennen kuin absoluuttipainovoiman tuloksista voidaan tehdä selkeitä johtopäätöksiä, tarvitaan lisää maannousututkimusta ja pidemmät korkealaatuiset aikasarjat useammalta asemalta Suomesta, sekä koko maannousun alueelta ja sen reunalta.

Julkaisun otsikon käännös	Geoidi ja maannousuun liittyvät painovoiman muutokset Suomessa
Alkuperäiskieli	Englanti
Pätevyys	Tohtorintutkinto
Myöntävä instituutio	Aalto-yliopisto
Valvoja/neuvonantaja	Vermeer, Martin, Vastuuprofessori Vermeer, Martin, Ohjaaja
Kustantaja	Aalto University
Painoksen ISBN	978-952-64-0298-7, 978-951-48-0270-6
Sähköinen ISBN	978-952-64-0299-4, 978-951-48-0271-3
Tila	Julkaistu - 2021
OKM-julkaisutyyppi	G5 Artikkeliväitöskirja

Tutkimusalat

geoidimallinnus
absoluuttipainovoima
painovoimatrendi
jääkauden jälkeinen maannousu
Suomi

Pääsy asiakirjaan

http://urn.fi/URN:ISBN:978-952-64-0299-4

Siteeraa tätä

@phdthesis{abe4b6c9dbf344618c6f2568e72ce12b,

title = "Geoid and postglacial rebound related gravity change in Finland",

abstract = "Positioning using Global Navigation Satellite Systems (GNSS) is widely used nowadays and it is getting more and more accurate. This requires also better geoid models for the transformation between heights measured with GNSS and heights in the national height system. In Finland heights are continuously changing due to the Fennoscandian postglacial rebound. Land uplift models are developed for the Fennoscandian land uplift area, not only for the vertical velocities, but also for the gravity change related to postglacial rebound. In this dissertation geoid studies were carried out in search of the geoid model that is most suitable for the conversion of GNSS heights in the EUREF-FIN coordinate system to heights in the Finnish height system N2000 on land as well as on sea. In order to determine the relationship between gravity change rates and vertical velocities, time series of absolute gravity measurements were analysed. Methods were tested for fitting a geoid model to GNSS-levelling data. The best method for Finland was found to be least-squares collocation in combination with cross-validation. The result was the height conversion surface FIN2005N00, the official model for Finland. Then, high-resolution global gravity field models were tested in geoid modelling for Finland. The resulting geoid models were better than the earlier geoid models for Finland. After correcting for an offset and tilt, the differences with other models disappeared. Also, a method was developed to validate geoid models at sea using GNSS measurements collected on a vessel. The method was successful and key elements were identified for the process of reducing the GNSS observations from the height of observation down to the geoid surface. Possible offsets between different types of absolute gravimeters were investigated by looking at the results of international comparisons, bi-lateral comparisons and of trend calculations. The trend calculations revealed significant offsets of 31.4 ± 10.9 μGal, 32.6 ± 7.4 μGal and 6.8 ± 0.8 μGal for the IMGC, GABL and JILAg-5 instruments. The time series of absolute gravity measurements at 12 stations in Finland were analysed. At seven stations reliable trends could be determined. Ratios between -0.206 ± 0.017 and -0.227 ± 0.024 μGal/mm and axis intercept values between 0.248 ± 0.089 and 0.335 ± 0.136 μGal/yr were found for the relationship between gravity change rates and vertical velocities. These values are larger than expected based on results of others. The knowledge obtained in the geoid studies will be of benefit in the determination of the next generation geoid models and height conversion surfaces for Finland. Before clear conclusions can be drawn from the absolute gravity results, more studies related to glacial isostatic adjustment, and longer high-quality time series from more stations in Finland, as well as the whole of the uplift area and its boundaries, are needed.",

keywords = "geoid modelling, validation, FIN2005N00, absolute gravimetry, gravity trend, postglacial rebound, glacial isostatic adjustment, Finland, geoidimallinnus, absoluuttipainovoima, painovoimatrendi, j{\"a}{\"a}kauden j{\"a}lkeinen maannousu, Suomi, geoid modelling, validation, FIN2005N00, absolute gravimetry, gravity trend, postglacial rebound, glacial isostatic adjustment, Finland",

author = "Mirjam Bilker-Koivula",

year = "2021",

language = "English",

isbn = "978-952-64-0298-7",

series = "Aalto University publication series DOCTORAL DISSERTATIONS",

publisher = "Aalto University",

number = "33",

address = "Finland",

school = "Aalto University",

}

TY - BOOK

T1 - Geoid and postglacial rebound related gravity change in Finland

AU - Bilker-Koivula, Mirjam

PY - 2021

Y1 - 2021

N2 - Positioning using Global Navigation Satellite Systems (GNSS) is widely used nowadays and it is getting more and more accurate. This requires also better geoid models for the transformation between heights measured with GNSS and heights in the national height system. In Finland heights are continuously changing due to the Fennoscandian postglacial rebound. Land uplift models are developed for the Fennoscandian land uplift area, not only for the vertical velocities, but also for the gravity change related to postglacial rebound. In this dissertation geoid studies were carried out in search of the geoid model that is most suitable for the conversion of GNSS heights in the EUREF-FIN coordinate system to heights in the Finnish height system N2000 on land as well as on sea. In order to determine the relationship between gravity change rates and vertical velocities, time series of absolute gravity measurements were analysed. Methods were tested for fitting a geoid model to GNSS-levelling data. The best method for Finland was found to be least-squares collocation in combination with cross-validation. The result was the height conversion surface FIN2005N00, the official model for Finland. Then, high-resolution global gravity field models were tested in geoid modelling for Finland. The resulting geoid models were better than the earlier geoid models for Finland. After correcting for an offset and tilt, the differences with other models disappeared. Also, a method was developed to validate geoid models at sea using GNSS measurements collected on a vessel. The method was successful and key elements were identified for the process of reducing the GNSS observations from the height of observation down to the geoid surface. Possible offsets between different types of absolute gravimeters were investigated by looking at the results of international comparisons, bi-lateral comparisons and of trend calculations. The trend calculations revealed significant offsets of 31.4 ± 10.9 μGal, 32.6 ± 7.4 μGal and 6.8 ± 0.8 μGal for the IMGC, GABL and JILAg-5 instruments. The time series of absolute gravity measurements at 12 stations in Finland were analysed. At seven stations reliable trends could be determined. Ratios between -0.206 ± 0.017 and -0.227 ± 0.024 μGal/mm and axis intercept values between 0.248 ± 0.089 and 0.335 ± 0.136 μGal/yr were found for the relationship between gravity change rates and vertical velocities. These values are larger than expected based on results of others. The knowledge obtained in the geoid studies will be of benefit in the determination of the next generation geoid models and height conversion surfaces for Finland. Before clear conclusions can be drawn from the absolute gravity results, more studies related to glacial isostatic adjustment, and longer high-quality time series from more stations in Finland, as well as the whole of the uplift area and its boundaries, are needed.

AB - Positioning using Global Navigation Satellite Systems (GNSS) is widely used nowadays and it is getting more and more accurate. This requires also better geoid models for the transformation between heights measured with GNSS and heights in the national height system. In Finland heights are continuously changing due to the Fennoscandian postglacial rebound. Land uplift models are developed for the Fennoscandian land uplift area, not only for the vertical velocities, but also for the gravity change related to postglacial rebound. In this dissertation geoid studies were carried out in search of the geoid model that is most suitable for the conversion of GNSS heights in the EUREF-FIN coordinate system to heights in the Finnish height system N2000 on land as well as on sea. In order to determine the relationship between gravity change rates and vertical velocities, time series of absolute gravity measurements were analysed. Methods were tested for fitting a geoid model to GNSS-levelling data. The best method for Finland was found to be least-squares collocation in combination with cross-validation. The result was the height conversion surface FIN2005N00, the official model for Finland. Then, high-resolution global gravity field models were tested in geoid modelling for Finland. The resulting geoid models were better than the earlier geoid models for Finland. After correcting for an offset and tilt, the differences with other models disappeared. Also, a method was developed to validate geoid models at sea using GNSS measurements collected on a vessel. The method was successful and key elements were identified for the process of reducing the GNSS observations from the height of observation down to the geoid surface. Possible offsets between different types of absolute gravimeters were investigated by looking at the results of international comparisons, bi-lateral comparisons and of trend calculations. The trend calculations revealed significant offsets of 31.4 ± 10.9 μGal, 32.6 ± 7.4 μGal and 6.8 ± 0.8 μGal for the IMGC, GABL and JILAg-5 instruments. The time series of absolute gravity measurements at 12 stations in Finland were analysed. At seven stations reliable trends could be determined. Ratios between -0.206 ± 0.017 and -0.227 ± 0.024 μGal/mm and axis intercept values between 0.248 ± 0.089 and 0.335 ± 0.136 μGal/yr were found for the relationship between gravity change rates and vertical velocities. These values are larger than expected based on results of others. The knowledge obtained in the geoid studies will be of benefit in the determination of the next generation geoid models and height conversion surfaces for Finland. Before clear conclusions can be drawn from the absolute gravity results, more studies related to glacial isostatic adjustment, and longer high-quality time series from more stations in Finland, as well as the whole of the uplift area and its boundaries, are needed.

KW - geoid modelling

KW - validation

KW - FIN2005N00

KW - absolute gravimetry

KW - gravity trend

KW - postglacial rebound

KW - glacial isostatic adjustment

KW - Finland

KW - geoidimallinnus

KW - absoluuttipainovoima

KW - painovoimatrendi

KW - jääkauden jälkeinen maannousu

KW - Suomi

KW - geoid modelling

KW - validation

KW - FIN2005N00

KW - absolute gravimetry

KW - gravity trend

KW - postglacial rebound

KW - glacial isostatic adjustment

KW - Finland

M3 - Doctoral Thesis

SN - 978-952-64-0298-7

SN - 978-951-48-0270-6

T3 - Aalto University publication series DOCTORAL DISSERTATIONS

PB - Aalto University

ER -

Geoid and postglacial rebound related gravity change in Finland

Abstrakti

Tutkimusalat

Pääsy asiakirjaan

Sormenjälki

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