Investigations of geoid models in Finland - Towards GNSS-related height system

Timo Saari

Investigations of geoid models in Finland - Towards GNSS-related height system

Julkaisun otsikon käännös: Geoidimallien tutkimukset Suomessa

Timo Saari

Finnish Geospatial Research Institute

Tutkimustuotos: Doctoral Thesis › Collection of Articles

Abstrakti

Jääkauden jälkeinen maankohoaminen muuttaa korkeuksia sekä niiden keskinäisiä suhteita Fenno-skandian alueella. Tästä johtuen, Suomen kansallinen korkeusjärjestelmä tulee päivittää sopivin välein. Korkeusjärjestelmät ovat perinteisesti perustuneet tarkkavaaitukseen, mikä on tarkka, mutta hidas, työläs sekä kallis menetelmä. Tässä väitöskirjassa tutkittiin moderneja, Global Navigation Satellite System (GNSS) -pohjaisia, korkeudenmääritysmenetelmiä, joilla voitaisiin korvata tarkkavaaitus Suomen seuraavaa kansallista korkeusjärjestelmää määritettäessä. GNSS-menetelmillä saadaan korkeus vertausellipsoidista, mikä on matemaattinen malli Maan muodosta. Ellipsoidikorkeuksilla ei täten ole sidosta fyysiseen Maan pintaan, eivätkä sisällä tietoa mihin suuntaan vesi virtaisi. Jotta ellipsoidikorkeuksille saadaan fyysinen merkitys, ja niitä voitaisiin käyttää kansallisissa korkeusjärjestelmissä, tarvitaan (kvasi)geoidimalli. GNSS-menetelmien arvioimisessa (kvasi)geoidimallien tarkkuuksilla on erittäin merkittävä rooli. Esitetyssä kenttäkokeessa vertailtiin korkeudenmääritysmenetelmiä, joista staattinen GNSS-mittaus osoittautui lupaavimmaksi. Menetelmällä on useita käytännön etuja tarkkavaaitukseen nähden, minkä lisäksi tulokset olivat hyvin lähellä toisiaan. Kokeessa kvasigeoidimallin sisältämät epävarmuudet kuitenkin mitätöityivät, johtuen havaintopisteiden läheisyydestä. Mallien epävarmuudet täytyisi huomioida laajemmissa, erityisesti valtakunnanlaajuisissa kampanjoissa. Suomen virallisen kvasigeoidimallin, FIN2005N00, julkaisemisen jälkeen painovoimasatelliitit Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) ja Gravity Recovery and Climate Experiment (GRACE) ovat mitanneet Maan painovoimakenttää ennennäkemättömällä tarkkuudella. Vertailimme kaikki tutkimuksemme aikaan saatavilla olevat GOCE- sekä GRACE-painovoimamallit Suomen alueella, missä tarkimmat mallit olivat jopa GOCE-satelliittia edeltäviä korkearesoluutioisia malleja tarkempia. Sopivin malli, DIR5, valittiin Suomen kvasigeoidi-laskentaan globaaliksi taustamalliksi, yhdessä EIGEN-6C4 kanssa. Kvasigeoidimallit arvioitiin Suomessa maa- ja merialueilla, joissa tutkimuksen uudet mallit olivat nykyisiä malleja tarkempia. Viimeisessä tutkimuksessa mittasimme Suomenlahdella GNSS-/painovoimakampanjan, jolla pyrittiin parantamaan sekä arvioimaan kvasigeoidimalleja merialueilla. Kampanjan painovoima-mittauksilla oli peräti 15 cm vaikutus kvasigeoidimalliin, mikä oli havaittavissa myös menetelmällä, jolla malleja arvioitiin GNSS-mittauksilla yhdessä merenpintamallien kanssa. Tämän väitöskirjan tulokset ovat merkittäviä Suomen seuraavan kansallisen kvasigeoidimallin luomiselle. Lisäksi, GNSS/geoidi -menetelmästä saatua tietoa tullaan hyödyntämään päätöksenteossa, missä valitaan menetelmä Suomen tulevan kansallisen korkeusjärjestelmän luomiselle.

Julkaisun otsikon käännös	Geoidimallien tutkimukset Suomessa
Alkuperäiskieli	Englanti
Pätevyys	Tohtorintutkinto
Myöntävä instituutio	Aalto-yliopisto
Valvoja/neuvonantaja	Nordman, Maaria, Vastuuprofessori Bilker-Koivula, Mirjam, Ohjaaja Poutanen, Markku, Ohjaaja
Kustantaja	Aalto University
Painoksen ISBN	978-952-64-1028-9
Sähköinen ISBN	978-952-64-1029-6
Tila	Julkaistu - 2022
OKM-julkaisutyyppi	G5 Artikkeliväitöskirja

Tutkimusalat

Geoidi
(kvasi)geoidimalli
valtakunnallinen korkeusjärjestelmä
painovoima
jääkauden jälkeinen maankohoaminen
Suomi

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http://urn.fi/URN:ISBN:978-952-64-1029-6

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@phdthesis{682934cab5fb48328e90fc45629d7255,

title = "Investigations of geoid models in Finland - Towards GNSS-related height system",

abstract = "In Fennoscandia, heights and their relations between each other are in constant change due to the post-glacial rebound, so the national height system needs to be updated occasionally. Traditionally, the update has been done with a method known as precise levelling, which is accurate but considered slow, laborious, and expensive. This dissertation studied the modern, mainly Global Navigation Satellite System (GNSS) -based, height determination techniques that could replace precise levelling as the method for the next national height system of Finland. GNSS-based techniques provide the height component relative to a reference ellipsoid, which is a mathematical surface and therefore lacks a physical connection to the Earth – i.e. have no information on the direction of water flow. Here, we need a (quasi-)geoid model to tie the ellipsoidal heights to the surface of the Earth and to national height systems. The (quasi-)geoid model's accuracy is therefore crucial with GNSS/geoid techniques. The presented case study gave us knowledge from several techniques. The static GNSS proved the most promising, as the result was close to the one from precise levelling. However, due to the closeness of the evaluation points, the relative error of the geoid between them is negligible in practice, which is not the case in a nationwide network. The national quasi-geoid model of Finland, FIN2005N00, was created nearly two decades ago. The gravity satellites, Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) and Gravity Recovery and Climate Experiment (GRACE), have since measured the Earth's gravitational field in unprecedented detail. At the time, we investigated all the published GOCE and GRACE global gravitational models (GGM) in Finland. We learned that the best models already performed at the same level or better than the pre-GOCE era high-resolution models. The most suitable model, DIR5, was chosen as a background model with the high-resolution EIGEN-6C4 in the quasi-geoid modelling of Finland. The new and present quasi-geoid models were evaluated on land and in sea areas. A significant improvement was achieved over the present models. A marine GNSS/gravity campaign was performed in the Gulf of Finland to improve the accuracy and validation of a quasi-geoid model in sea areas. Geoid height differences of up to 15 cm were found with the new gravity data included in the quasi-geoid modelling. The result was confirmed in the evaluation with marine GNSS measurements in combination with sea surface models. This dissertation's results will be important for producing the next national quasi-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.",

keywords = "geoid, (quasi-)geoid model, GNSS, national height system, GOCE, GRACE, gravity, post-glacial rebound, Finland, Geoidi, (kvasi)geoidimalli, valtakunnallinen korkeusj{\"a}rjestelm{\"a}, painovoima, j{\"a}{\"a}kauden j{\"a}lkeinen maankohoaminen, Suomi, geoid, (quasi-)geoid model, GNSS, national height system, GOCE, GRACE, gravity, post-glacial rebound, Finland",

author = "Timo Saari",

year = "2022",

language = "English",

isbn = "978-952-64-1028-9",

series = "Aalto University publication series DOCTORAL THESES",

publisher = "Aalto University",

number = "171",

address = "Finland",

school = "Aalto University",

}

TY - BOOK

T1 - Investigations of geoid models in Finland - Towards GNSS-related height system

AU - Saari, Timo

PY - 2022

Y1 - 2022

N2 - In Fennoscandia, heights and their relations between each other are in constant change due to the post-glacial rebound, so the national height system needs to be updated occasionally. Traditionally, the update has been done with a method known as precise levelling, which is accurate but considered slow, laborious, and expensive. This dissertation studied the modern, mainly Global Navigation Satellite System (GNSS) -based, height determination techniques that could replace precise levelling as the method for the next national height system of Finland. GNSS-based techniques provide the height component relative to a reference ellipsoid, which is a mathematical surface and therefore lacks a physical connection to the Earth – i.e. have no information on the direction of water flow. Here, we need a (quasi-)geoid model to tie the ellipsoidal heights to the surface of the Earth and to national height systems. The (quasi-)geoid model's accuracy is therefore crucial with GNSS/geoid techniques. The presented case study gave us knowledge from several techniques. The static GNSS proved the most promising, as the result was close to the one from precise levelling. However, due to the closeness of the evaluation points, the relative error of the geoid between them is negligible in practice, which is not the case in a nationwide network. The national quasi-geoid model of Finland, FIN2005N00, was created nearly two decades ago. The gravity satellites, Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) and Gravity Recovery and Climate Experiment (GRACE), have since measured the Earth's gravitational field in unprecedented detail. At the time, we investigated all the published GOCE and GRACE global gravitational models (GGM) in Finland. We learned that the best models already performed at the same level or better than the pre-GOCE era high-resolution models. The most suitable model, DIR5, was chosen as a background model with the high-resolution EIGEN-6C4 in the quasi-geoid modelling of Finland. The new and present quasi-geoid models were evaluated on land and in sea areas. A significant improvement was achieved over the present models. A marine GNSS/gravity campaign was performed in the Gulf of Finland to improve the accuracy and validation of a quasi-geoid model in sea areas. Geoid height differences of up to 15 cm were found with the new gravity data included in the quasi-geoid modelling. The result was confirmed in the evaluation with marine GNSS measurements in combination with sea surface models. This dissertation's results will be important for producing the next national quasi-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.

AB - In Fennoscandia, heights and their relations between each other are in constant change due to the post-glacial rebound, so the national height system needs to be updated occasionally. Traditionally, the update has been done with a method known as precise levelling, which is accurate but considered slow, laborious, and expensive. This dissertation studied the modern, mainly Global Navigation Satellite System (GNSS) -based, height determination techniques that could replace precise levelling as the method for the next national height system of Finland. GNSS-based techniques provide the height component relative to a reference ellipsoid, which is a mathematical surface and therefore lacks a physical connection to the Earth – i.e. have no information on the direction of water flow. Here, we need a (quasi-)geoid model to tie the ellipsoidal heights to the surface of the Earth and to national height systems. The (quasi-)geoid model's accuracy is therefore crucial with GNSS/geoid techniques. The presented case study gave us knowledge from several techniques. The static GNSS proved the most promising, as the result was close to the one from precise levelling. However, due to the closeness of the evaluation points, the relative error of the geoid between them is negligible in practice, which is not the case in a nationwide network. The national quasi-geoid model of Finland, FIN2005N00, was created nearly two decades ago. The gravity satellites, Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) and Gravity Recovery and Climate Experiment (GRACE), have since measured the Earth's gravitational field in unprecedented detail. At the time, we investigated all the published GOCE and GRACE global gravitational models (GGM) in Finland. We learned that the best models already performed at the same level or better than the pre-GOCE era high-resolution models. The most suitable model, DIR5, was chosen as a background model with the high-resolution EIGEN-6C4 in the quasi-geoid modelling of Finland. The new and present quasi-geoid models were evaluated on land and in sea areas. A significant improvement was achieved over the present models. A marine GNSS/gravity campaign was performed in the Gulf of Finland to improve the accuracy and validation of a quasi-geoid model in sea areas. Geoid height differences of up to 15 cm were found with the new gravity data included in the quasi-geoid modelling. The result was confirmed in the evaluation with marine GNSS measurements in combination with sea surface models. This dissertation's results will be important for producing the next national quasi-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.

KW - geoid

KW - (quasi-)geoid model

KW - GNSS

KW - national height system

KW - GOCE

KW - GRACE

KW - gravity

KW - post-glacial rebound

KW - Finland

KW - Geoidi

KW - (kvasi)geoidimalli

KW - valtakunnallinen korkeusjärjestelmä

KW - painovoima

KW - jääkauden jälkeinen maankohoaminen

KW - Suomi

KW - geoid

KW - (quasi-)geoid model

KW - GNSS

KW - national height system

KW - GOCE

KW - GRACE

KW - gravity

KW - post-glacial rebound

KW - Finland

M3 - Doctoral Thesis

SN - 978-952-64-1028-9

T3 - Aalto University publication series DOCTORAL THESES

PB - Aalto University

ER -

Investigations of geoid models in Finland - Towards GNSS-related height system

Abstrakti

Tutkimusalat

YK:n kestävän kehityksen tavoitteet

Pääsy asiakirjaan

Sormenjälki

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