Observations of Artificial Radio Sources within the Framework of Geodetic Very Long Baseline Interferometry
Doktorsavhandling, 2020

Very long baseline interferometry (VLBI) is a mature and fascinating technique with unique and indisputable applications in radio astronomy, planetary sciences, and space geodesy. The latter discipline is a field of science facilitating our understanding of various global-scale phenomena connected to Earth dynamics. Space geodesy provides, in the microwave regime, accurate and long-term stable celestial and terrestrial reference frames, to which those environmental changes can be properly referenced and their spatio-temporal variability can be subsequently accurately investigated. In order to attain better knowledge on complex, and yet subtle, geodynamical phenomena of scientific and economic importance, there is a need for an improved global geodetic infrastructure and enhanced quality of space-geodetic measurements. The common effort of the geodetic community known as the Global Geodetic Observing System (GGOS) shall address that need and provide the highest possible accuracy of geodetic products and reference frames as well as the high consistency across space-geodetic techniques. The ambitious goals of GGOS necessitate appropriate changes to be made also in the area of geodetic/astrometric VLBI, realized at preset in the form of the VLBI Global Observing System (VGOS), a next-generation system aiming to meet the requirements of GGOS and deliver geodetic products with an unprecedented quality. In order to make VGOS succeed, the key components of this complex system need to be refined, including also new observing concepts and scheduling strategies, in order to fully exploit the enhanced performance that this system can bring. Thanks to its characteristics, VGOS creates also a great opportunity for extending the current VLBI research with new applications, for the benefit of the scientific community and society at large.
The subject of this thesis concerns observations of artificial radio sources within the framework of geodetic VLBI, in connection to both the current VLBI system and VGOS. This includes information on the combination of observations of natural radio sources and satellite/lunar objects as well as benefits and challenges related to the observing strategy and the technical feasibility of the presented concept. The thesis is based mostly on extensive simulation studies concerning objects on the Moon and geodetic Earth-orbiting satellites, but it also includes an analysis of VLBI observations of the lunar lander performed during dedicated experiments and with a global network of radio telescopes. The information content of this thesis may be treated as a further step towards global observations of artificial radio sources with VLBI in the VGOS era and stimulate new observing concepts for space geodesy.

space geodesy

Monte-Carlo simulations

VGOS

geodetic VLBI

c5++

Chalmers University of Technology. Online defense.
Opponent: Dr. John M. Gipson, Chief Scientist, NASA/GSFC, NVI INC., USA

Författare

Grzegorz Klopotek

Chalmers, Rymd-, geo- och miljövetenskap, Onsala rymdobservatorium, Rymdgeodesi och geodynamik

Geodetic VLBI with an artificial radio source on the Moon: a simulation study

Journal of Geodesy,; Vol. 92(2018)p. 457-469

Artikel i vetenskaplig tidskrift

Position determination of the Chang’e 3 lander with geodetic VLBI

Earth, Planets and Space,; Vol. 71(2019)

Artikel i vetenskaplig tidskrift

Klopotek G, Hobiger T, Haas R, Otsubo T (2020). Geodetic VLBI for precise orbit determination of Earth satellites: A simulation study

Tekniken som kallas långbasinterferometri (på engelska very long baseline interferometry, VLBI) har många tillämpningar i radioastronomi, planetforskning och rymdgeodesi. Rymdgeodesi är en vetenskap som studerar jordens form, orientering och storlek med hjälp av satelliter och andra objekt i rymden. När långbasinterferometri används för rymdgeodesi kallas det geodetisk VLBI, vilket används för att mäta hur jorden roterar och deformeras. Rymdgeodetiska tekniker, som geodetisk VLBI, förser oss också med noggranna och stabila referensramar. Dessa referensramar behövs för att bland annat kunna mäta långtidsförändringar i klimat och miljö, och för att se deras variationer i tid och rum.
I VLBI observeras radiovågor från avlägsna, ljusstarka galaxer (så kallade kvasarer) med nätverk av radioteleskop. När man observerar kvasarer samtidigt med två teleskop kan skillnaden i signalernas ankomsttid användas för att bestämma avståndet mellan teleskopen. Men inte bara det, när man observerar många olika radiokällor med flera teleskop i olika delar av världen, kan man också bestämma jordens rotation. Geodetisk VLBI är den enda teknik som kan bestämma alla rotationsparametrar. Tekniken bidrar också till att skapa och upprätthålla gemensamma referensramar för hela jorden. Det som gör VLBI unikt är att den knyter ihop den jordbaserade och den rymdbaserade referensramen. Det geodetiska VLBI systemet vidareutvecklas just nu till nästa generation som kallas VGOS (från engelska VLBI Global Observing System). Det nya systemet består av mindre och snabbare teleskop, och kommer att ge mera noggranna mätningar med högre tidsupplösning. VGOS ger också stora möjligheter att utvidga VLBI-forskning med nya tillämpningar.
Denna avhandling avser observationer av artificiella radiokällor inom ramen av geodetisk VLBI, både i relation till nuvarande VLBI-systemet och till VGOS. Bland annat studeras hur observationer av satelliter och radiokällor på månen kan kombineras med traditionella VLBI-mätningar, och vilka fördelar och utmaningar detta innebär. En stor del av avhandlingen fokuserar på simulationer av sådana mätningar, men avhandlingen inneåller också analys av verkliga VLBI-observationer av en månlandare från special-designade experiment som genomfördes med ett globalt nätverk av radioteleskop. Avhandlingen kan ses som ett ytterligare steg mot globala observationer av artificiella radiokällor med VLBI i VGOS-eran och kan samtidigt leda till nya observationskoncept för rymdgeodesi.

The technique called very long baseline interferometry (VLBI) has many applications in radio astronomy, planetary sciences and space geodesy. Space geodesy is a science that studies Earth's shape, its orientation, and its size with the use of satellites and other objects in space. When very long baseline interferometry is used for space geodesy, it is referred to as geodetic VLBI and is utilized to measure how Earth rotates and is deformed. Space-geodetic techniques, such as geodetic VLBI, provide us also with accurate and stable reference frames. Those reference frames are required in order to measure long-term changes in the climate and environment, and investigate their variation in time and space.
In VLBI radiowaves from very distant, radio-loud galaxies (so-called quasars), are observed with networks of radio telescopes. When one observes quasars with two telescopes simultaneously, the difference in signal reception is used to determine the distance between these telescopes. Not only that, when one observes many radio sources with several radio telescopes located at different parts of the world, one can also determine Earth rotation. Geodetic VLBI is the only technique that can determine all rotation parameters. This techniques contibutes also to establishement and maintenance of common reference frames for the whole Earth. What makes VLBI unique is that it links the terrestrial and space-based reference frames. The geodetic VLBI system is currently being further developed into the next-generation system called VGOS (VLBI Global Observing System). This new system consists of smaller and faster telescopes, and shall provide more accruacte observations with higher temporal resolution. VGOS offers also great opportunities to expand VLBI research with new applications.
This thesis concerns observations of artificial radio sources within the framework of geodetic VLBI, in relation to both the current VLBI system and VGOS. Among other apsects, it is studied how observations of satellites and radio sources on the Moon can be combined with traditional VLBI measurements, and what advantages and challenges this concept brings. A large part of the dissertation focuses on simulations of such measurements, but this thesis contains also an analysis of real VLBI observations of a lunar lander carried out from specially designed experiments conducted with a global network of radio telescopes. This dissertation can be treated as a further step towards global observations of artificial radio sources with VLBI in the VGOS era and, at the same time, can lead to new observing concepts for space geodesy.

Drivkrafter

Hållbar utveckling

Ämneskategorier

Annan geovetenskap och miljövetenskap

Miljövetenskap

Multidisciplinär geovetenskap

Fundament

Grundläggande vetenskaper

Infrastruktur

C3SE (Chalmers Centre for Computational Science and Engineering)

Onsala rymdobservatorium

ISBN

978-91-7905-275-1

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4742

Utgivare

Chalmers tekniska högskola

Chalmers University of Technology. Online defense.

Online

Opponent: Dr. John M. Gipson, Chief Scientist, NASA/GSFC, NVI INC., USA

Mer information

Senast uppdaterat

2020-04-16