OBSERVED AND PREDICTED DATA IN RADIO ASTROMETRIC OBSERVATIONS

Abstract

ABSTRACT Atmospheric effects are the main source of erros in astrometry by connected-element radio interferometry. An improvement to this situation can be obtained by taking account of the changing atmospheric states. In this work it is shown that the monitoring of near-ground-level gradients of the radio refractivity index parameters would be of use when analyzing the differences between observed and predicted data, on which the astrometric results are based. A discussion of the mechanisms by which the atmospheric effects disturb the radio astrometric results is presented. Practical experiments are reported, which support the obtained conclusions. The raw data from these measurements are appended. The analysis is further extended to ionospheric effects. The expressions for polar motion and annual aberration are also thoroughly considered. We have then been able to analyze the almost 15 years of 5 GHz positional results from the MRAO/5km Telescope. The details of each observation are listed and appended. The analysis of this long series of results has enabled an accurate determination of the main terms of the luni-solar precession and of the nutation. The work related in this dissertation indicates that a degree of optimization of the positional measurements can be achieved by monitoring the atmospheric gradients. It also indicates that the mean MRAO/5km Telescope astrometric results are consistent to a very high level; this is substantiated by the precessional and nutational corrections obtained.