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.
Chalmers, Rymd-, geo- och miljövetenskap, Onsala rymdobservatorium, Rymdgeodesi och geodynamik
Journal of Geodesy,; Vol. 92(2018)p. 457-469
Artikel i vetenskaplig tidskrift
Earth, Planets and Space,; Vol. 71(2019)
Artikel i vetenskaplig tidskrift
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.
Annan geovetenskap och miljövetenskap
C3SE (Chalmers Centre for Computational Science and Engineering)
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4742
Chalmers tekniska högskola
Chalmers University of Technology. Online defense.
Opponent: Dr. John M. Gipson, Chief Scientist, NASA/GSFC, NVI INC., USA