Year: 2002
Type: dissertation
Abstract: The performance of astronomical interferometer arrays operating at (sub)millimeter wave lengths is seriously compromised by rapid variations of atmospheric water vapour content that distort the phase coherence of incoming celestial signals.Unless corrected, these phase distortions, which vary rapidly with time and from antenna to antenna, seriously com promise the sensitivity and image quality of these arrays.Building on the success of a prototype infrared radiometer for millimeter astronomy (IRMA I), which was used to mea sure atmospheric water vapour column abundance, this thesis presents results from a second generation radiometer (IRMA II) operating at the James Clerk Maxwell Telescope (JCMT) on Mauna Kea, Hawaii from December, 2000 to March, 2001.These results include com parisons with other measures of water vapour abundance available on the summit of Mauna Kea and a comparison with a theoretical curve-of-growth calculated from a new radiative transfer model, ULTRAM, developed specifically for the purpose.Plans for a third gener ation radiometer (IRMA III) are also be discussed.V vi Contents List of Figures ix List of Tables xii List of Tables 2.1 Radiometric quantities and associated units 2.2 Temperature dependence of rotational partition function for common molec ular species 3.1 Default ULTRAM layer thicknesses 3.2 Radiative transfer modelling parameters for the submillimeter and mid-infrared regions 4.1 Parabolic mirror design parameters 4.2 Infrared detector parameters 5.1 Conversion factors for the IRMA curve-of-growth as determined by instru mental zenith pwv measurements 6.1 Comparison of IRMA I and IRMA II water vapour column abundance reso lutions at 0.5 and 1.0 mm pwv 6.2 Comparison of IRMA I and IRMA II excess electromagnetic path length resolutions at 0.5 and 1.0 mm pwv
Author: Ian M. Chapman
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W751054511