An investigation of GNSS radio occultation atmospheric sounding technique for Australian meteorology

The Earth’s atmosphere is critical to the environment and lives on the Earth. Atmospheric studies play an important role in many scientific areas and in particular meteorology. However, observing the atmosphere in a high resolution and accuracy is a challenging task due to its dynamic nature and complexity of its processes. Current ground-based observations and satellite remote sensing techniques have critical limitations. Better observation techniques are desirable to capture the detailed status and processes of the atmosphere properly. <br><br>Recent developments of the Global Navigation Satellite Systems (GNSS) radio occultation (RO) technique have offered an exciting potential for meteorological research. The basic idea of this emerging technique is to use radio signals between the Low Earth Orbit (LEO) and GNSS satellites to probe the Earth's atmosphere and ionosphere from space. Through a number of experimental missions and related studies since 1995, GNSS RO has demonstrated many unprecedented advantages over other atmospheric observation methods. <br><br>The main aim of this thesis is to investigate the key theoretical and practical interests of the Australian meteorological community using GNSS RO. A comprehensive literature review is conducted to explore the fundamentals, the developments and challenges of the GNSS RO. The next generation GNSS RO missions, with the advantages of the multiple constellations, multiple signals and multiple systems, will have significant impacts and improvement in both quantity and quality of observations. A mission simulation study is undertaken to examine Australia’s opportunities from these future missions. In order to address the challenges of real time applications, an investigation is also conducted into the system architecture of the satellite data centre for the mega data storage and processing. These studies into the GNSS RO missions and the data processing provide a good benchmark for the planning of future international and Australian missions.<br><br>Detailed statistic analyses are carried out to assess the atmospheric profiles derived from the GNSS RO against other atmospheric measurements and modelled data. Four studies apply advanced statistic tools and data warehouse techniques on the large volume meteorological database to extract the error characteristics of the new atmospheric observation data sources. The results, spatial and temporal error characteristics of the new datasets, can assist meteorological researchers incorporating the RO technique into the existing meteorological systems. The impact of the co-location criteria between the resulting datasets is also examined.<br><br>This thesis presents studies in climatological applications using GPS RO data. One study is undertaken to examine the temperature trends over the Antarctic using both radiosonde and CHAMP RO data. Significant lower stratospheric cooling and tropospheric warming have been found over the Antarctic for the past five decades (1956-2010) using Australian radiosonde data. Temperature trends are also derived using seven years of CHAMP RO data and compared with the data from collocated radiosonde stations. The other study is designed to investigate the tropopause over the Australasian region using GPS FORMOSAT 3/COSMIC RO temperature profiles. The study results confirm that the FORMOSAT 3/COSMIC RO temperature profiles show more details of the atmosphere and the tropopause characteristics than other observation methods.<br>