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Nadir dependent GNSS code biases and their effect on 2D and 3D ionosphere modeling
KTH, School of Architecture and the Built Environment (ABE), Real Estate and Construction Management, Geodesy and Satellite Positioning. Lantmäteriet – The Swedish Mapping, Cadastral, and Land Registration Authority.ORCID iD: 0000-0001-8871-2659
2020 (English)In: Remote Sensing, ISSN 2072-4292, E-ISSN 2072-4292Article in journal (Refereed) Submitted
Abstract [en]

Recent publications have shown that group delay variations are present in the code observables of the BeiDou system, as well as to a lesser degree in the code observables of the GPS. These variations could potentially affect precise point positioning, integer ambiguity resolution by the Hatch-Melbourne-Wübbena linear combination, as well as total electron content estimation for ionosphere modeling from GNSS observations. The latter is an important characteristic of the ionosphere and a prerequisite in some applications of precise positioning. By analyzing the residuals from total electron content estimation, the existence of group delay variations is in this study confirmed by a method independent of methods previously used. It also provides knowledge of the effects of group delay variations on ionosphere modeling. These biases are confirmed both for 2-dimesional ionosphere modeling by the thin shell model, as well as for 3-dimensional ionosphere modeling using tomographic inversion. BeiDou group delay variations are prominent and consistent in the residuals for both the 2-dimensional and 3-dimensional case of ionosphere modeling, while GPS group delay variations are smaller and cannot be confirmed due to the accuracy limitations of the ionospheric models. Group delay variations are to a larger extent absorbed by the ionospheric model when 3-dimensional ionospheric tomography is performed in comparison with 2-dimensional modeling.

Place, publisher, year, edition, pages
MDPI, 2020.
Keywords [en]
GNSS, Group delay variations, Biases, Nadir dependence, Ionosphere modeling, Ionospheric tomography
National Category
Other Engineering and Technologies
Identifiers
URN: urn:nbn:se:kth:diva-267043OAI: oai:DiVA.org:kth-267043DiVA, id: diva2:1390357
Note

QC 20200203

Available from: 2020-01-31 Created: 2020-01-31 Last updated: 2020-02-03Bibliographically approved
In thesis
1. GNSS hardware biases in code and carrier phase observables
Open this publication in new window or tab >>GNSS hardware biases in code and carrier phase observables
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

GNSS hardware biases appear in code and phase observations, and originates both from the receiver and satellite hardware. The presence of biases in GNSS observations might affect the accuracy in precise GNSS positioning applications, and might also be of relevance in other GNSS applications. They may also be a cause of incompatibility between different receiver types or GNSS constellations.

In this thesis, which is based on four papers, the biases in GNSS code and carrier phase observables are investigated. This is done by: characterizing and analyzing some selected biases; revealing some previously unknown biases; developing new methods to estimate some of the biases; and compiling and presenting information about biases in a new and comprehensive way.

Paper 1 gives a full review of how various kinds of biases affect various applications of precise GNSS positioning, including multi-GNSS positioning and ambiguity resolved PPP.

In Paper 2, two cases of relative phase biases, that potentially could degrade the positioning accuracy in precise positioning applications, are investigated. Fortunately, these biases turns out to be small in size with negligible effect on the positioning accuracy in both cases, which involves relative between-receivers biases for receivers of different type and between-signals biases for carrier phase observations of different signals associated with the same carrier frequency.

Paper 3 characterizes GNSS observations from a Nexus 9 Android tablet. By doing this, it reveals a number of earlier unknown biases. A drift between the code and phase observable of -3 and 2 mm/s is revealed for GPS and GLONASS, respectively. Additionally, an unexpected variation in the GLONASS phase observable, which seems to be dependent on the topocentric range rate of the satellite, is discovered.

In Paper 4, the existence of nadir dependent code biases is confirmed for GNSS observations from BeiDou-2 satellites of the BeiDou constellation by analyzing the residuals of 2-D and 3-D ionosphere modeling. This a new method to derive this kind of bias, independent of the earlier employed approach based on the multipath linear combination. The estimated effect is, however, too small to infer a similar nadir dependence for GPS and Galileo as well.

Abstract [sv]

Hårdvaru-relaterade GNSS biases uppträder i kod- och bärvågsobservationer som små avvikelser eller fel. Dessa är karaktäristiska för en viss typ av hårdvara och har sitt ursprung både i satellit och mottagare. Förekomsten av biases i GNSS-observationer har en potentiell negative påverkan för mätosäkerheten för tillämpningar av noggrann GNSS-positionering. Även i andra GNSS-tillämpningar kan biases i vissa fall vara relevanta. Förekomsten av biases kan också vara en orsak till kompatibilitetsproblem när GNSS-observationer från olika mottagartyper eller GNSS-konstellationer kombineras.

Denna avhandling, som är baserad på fyra artiklar, tittar närmare på biases som förekommer i kod- och bärvågsobservationer. Mer specifikt så involverar detta: karaktärisering och analys av några utvalda biases; avlöjande av vissa tidigare okända biases; utvecklande av nya metoder för estimering av biases; och sammanställning och presentation av biases på ett nytt och övergripande sätt.

Artikel 1 är en litteraturstudie som behandlar hur olika typer av biases påverkar tillämpningar för noggrann GNSS-positionering. Dessa tillämpingar innefattar bland annat GNSS-positionering som involverar flera GNSS-konstellationer och PPP med heltalslösning av periodobekanta.

Artikel 2 undersöker två typer av relativa biases för bärvågsobservationer. Dessa skulle potentiellt sett kunna ha en negativ inverkan på mätosäkerheten för noggranna GNSS-tillämpningar. De två typerna innefattar biases relativa mellan två mottagare, och biases relativa mellan två signaler. Lyckligtvis så visade det sig att dessa är så små att de endast har en försumbar effekt i de flesta GNSS-tillämpningar.

I artikel 3 karaktäriseras GNSS-observationerna från en surfplatta av modell Nexus 9 och med Android som operativsystem. Här avslöjas två tidigare okända biases: drift mellan kod- och bärvågsobservablerna motsvarande -3 och 2 mm/s för GPS och Glonass; samt en variation i Glonass bärvågsobservabel som verkar bero på den topocentriska hastigheten.

Artikel 4 bekräftar förekomsten av ett nadir-beroende för kod-biases för BeiDou-observationer gällande de satelliter som betecknas BeiDou-2. Detta resultat är härlett från jonosfärsmodellering i två och tre dimensioner genom analys av motsvarande residualer. Den presenterade metoden för denna härledning är ny, då metoden utnyttjad i tidigare studier istället använder sig av flervägsfelslinjärkombinationen av kod- och bärvågsobservationer.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2020. p. 56
Series
TRITA-ABE-DLT ; 203
Keywords
GNSS, GNSS positioning, hardware biases, phase biases, multi-GNSS, GPS, GLONASS, Galileo, BeiDou, satellite dependency, characterization, android, mass market, Group delay variations, nadir dependence, ionosphere modeling, ionospheric tomography
National Category
Electrical Engineering, Electronic Engineering, Information Engineering Other Engineering and Technologies Geotechnical Engineering
Research subject
Geodesy and Geoinformatics; Geodesy and Geoinformatics, Geodesy
Identifiers
urn:nbn:se:kth:diva-267044 (URN)978-91-7873-454-2 (ISBN)
Public defence
2020-02-28, F3, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20200104

Available from: 2020-02-04 Created: 2020-01-31 Last updated: 2020-02-04Bibliographically approved

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