Improving geodetic VLBI: UT1 accuracy, latency of results, and data quality monitoring

Loading...
Thumbnail Image
Journal Title
Journal ISSN
Volume Title
School of Electrical Engineering | Doctoral thesis (monograph) | Defence date: 2013-06-14
Checking the digitized thesis and permission for publishing
Instructions for the author
Date
2013
Department
Radiotieteen ja -tekniikan laitos
Department of Radio Science and Engineering
Major/Subject
Mcode
Degree programme
Language
en
Pages
164
Series
Aalto University publication series DOCTORAL DISSERTATIONS, 88/2013
Abstract
In modern geodesy the space-related techniques play an important role. The three most significant of these techniques are the Global Navigation Satellite System (GNSS) that includes the Global Positioning System (GPS), the Satellite Laser Ranging (SLR), and Very Long Baseline Interferometry (VLBI). The next generation geodetic VLBI system, VLBI2010, covers everything from antennas to analysis and is being implemented at VLBI stations globally. One of the key requirements for VLBI2010 is the automation of the data analysis in order to reduce the latency of the results to 24 hours. VLBI is a unique technique for determining the Earth Orientation Parameters (EOP), which are necessary, for example, for navigation satellites. The accuracy of GNSS positioning is related to the accuracy of EOP. Therefore, it is important to measure these parameters with the best possible accuracy and as short latency as possible. In this dissertation the automation of the International VLBI Service for geodesy and astrometry (IVS) intensive sessions is described. In the near future, the Vienna VLBI Software (VieVS) will be implemented with the pre-analysis steps that are currently being developed, the group delay ambiguity resolution and the ionospheric correction. The most commonly used geodetic VLBI analysis software is Calc/Solve that is maintained at the Goddard Space Flight Center (GSFC). So as not to bias the outcome by adopting only one software package, a comparison of Solve and VieVS EOP results was performed. This comparison showed that VieVS analysis appeared to improve the accuracy in the dUT1 result. However, polar motion results were more precise when Solve was used for the analysis. To fulfill the VLBI2010 precision requirements, the effect of source distribution on the dUT1 result accuracy obtained from IVS INT1 experiments was investigated. On the basis of the research conducted in this thesis, the results from the source constellation study show that the accuracy of the dUT1 is affected by the distribution in the sky as seen from the midpoint of a baseline, and will improve when a novel method proposed for scheduling intensive sessions will be implemented. Until now, the sky has been observed from the Kokee Park North direction. Introducing the new concept of observing the sky from a fictitious midpoint of the baseline greatly improves dUT1 accuracy. IVS should take this into consideration, because the accuracy of the results is a significant factor when calculating satellite orbits, for example. VLBI2010 requires shipment of the VLBI data via Internet. Firmware was developed to enable VLBI2010-compatible stations to perform zero baseline correlation tests with the Digital Base Band Converter (DBBC) and FILA10G ethernet board, and thus the stations can check the quality of the data in real-time.

Modernissa geodesiassa avaruustekniikoilla on tärkeä rooli. Kolme tärkeintä tekniikkaa ovat globaali satelliittipaikannusjärjestelmä (Global Navigation Satellite System, GNSS, mukaan lukien Global Positioning System, GPS), satelliittilaser (Satellite Laser Ranging, SLR) ja pitkäkantainterferometria (Very Long Baseline Interferometry, VLBI). Seuraavan sukupolven geodeettinen VLBI-järjestelmä, VLBI2010, kattaa kaiken antenneista data-analyysiin. Yksi tärkeimmistä vaatimuksista on analyysin automatisointi, jonka avulla tulokset on mahdollista saada 24 tunnin sisällä korrelloinnista. Tässä väitöskirjassa kansainvälisen geodesian ja astrometrian VLBI-palvelun (International VLBI Service for geodesy and astrometry, IVS) intensiivisessioiden analysointi on automatisoitu sekä Vienna VLBI Software -ohjemistoon (VieVS) lisätään puuttuvia esianalyysivaiheita. Goddard Space Flight Centerin (GSFC) ylläpitämä Calc/Solve-ohjelmisto on yleisimmin käytössä oleva geodeettisen VLBI:n analyysityökalu. Jotta tuloksiin ei tulisi systemaattista virhettä, kun käytetään vain yhtä ohjelmistoa, uudemman VieVS:in tuloksia verrattiin Solven tuloksiin. VieVS antaa tarkempia dUT1-tuloksia, kun taas Solven napavariaatiotulokset olivat tarkempia kuin VieVSin. Jotta VLBI2010-tarkkuusvaatimukset voitaisiin täyttää, tutkittiin dUT1-tuloksia IVS:n INT1-sessioista. Oletuksena oli, että lähteiden sijainti taivaalla kahta teleskooppia yhdistävän viivan keskipisteestä nähtynä vaikuttaa parametriin ja sen virheeseen. Tutkimuksessa todettiin, että ne sessiot, joissa kohteet olivat mahdollisimman kaukana toisistaan, tuottivat tarkimmat tulokset. Väitöskirjatutkimuksessa kirjoitettiin VHDL-firmware niin kutsuttuja 'zero baseline correlation' -testejä varten, joiden avulla voidaan tutkia VLBI-datan laatua.
Description
Supervising professor
Hallikainen, Martti, Prof., Aalto University, Finland
Thesis advisor
Tornikoski, Merja, Dr., Aalto University, Finland
Poutanen, Markku, Prof., Finnish Meteorological Institute, Finland
Keywords
Very Long Baseline Interferometry, VLBI, geodesy, UT1, VHDL, VHSIC Hardware Description Language, geodesia
Other note
Citation