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An Investigation of GNSS Radio Occultation Atmospheric Sounding

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An Investigation of GNSS Radio Occultation Atmospheric Sounding An Investigation of GNSS Radio Occultation Atmospheric Sounding Technique for Australian Meteorology A thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy Erjiang Fu B.S. School of Mathematical and Geospatial Sciences College of Science, Engineering and Health RMIT University August 2011 I (This page intentionally left blank) II Declaration I certify that except where due acknowledgement has been made, the work is that of the author alone; the work has not been submitted previously, in whole or in part, to qualify for any other academic award; the content of the thesis is the result of work which has been carried out since the official commencement date of the approved research program; any editorial work, paid or unpaid, carried out by a third party is acknowledged; and, ethics procedures and guidelines have been followed. Erjiang Fu I (This page intentionally left blank) II Acknowledgements First of all, I would like to thank my supervisors: Professor Kefei Zhang, Dr David Silcock and Dr Yuriy Kuleshov. This thesis would not have been possible without their inspiration, guidance, support and encouragement in the past four years. Especially, my main supervisor Professor Zhang, also one of my close friends, who opened the door of a scientific career for me. During the research journey, it was my greatest honour to work with many respectable scientists and researchers. Sincere thanks go to Professor Yuei-An Liou, Professor Alexander Pavelyev, Dr Xiaolan Wang, Dr Kaye Marion, Dr Suqin Wu, Dr Chuan-Sheng Wang, Dr Robert Norman, Dr Gang-Jun Liu, Dr Falin Wu, Dr Xiaohua Xu, Dr Sue Choy, Dr Xinjia Zhou, Dr Yan Wang, Dr Dongju Peng, Dr Ming Zhu, Mr Bobby Wong, Mr Toby Manning, Miss Ying Li, Ms Jing Peng, Mr Stuart Whitman, Mr Alex Chen, Miss Gap Vimvipa, and others. I would also like to thank the institutions that have given me access to their data and software systems, which are critical to this research. These institutions include the Australian Bureau of Meteorology, Constellation Observing System for Meteorology Ionosphere and Climate Office at UCAR (University Corporation for Atmospheric Research USA), Global Environmental and Earth Science Information System at NASA (National Aeronautics and Space Administration USA), University of Graz, Reference Antarctic Data for Environmental Research, and European GRAS Meteorology. This PhD program is financially supported by RMIT Platform Research Institute. The research is also partially supported by a number of funded research projects endorsed to my supervisors Prof Kefei Zhang and Dr Yuriy Kuleshov: • Australian Space Innovation and Research Project: Platform technologies for space, atmosphere and climate ($2.8 million, 2010 - 2013) • Australia International Science Linkage Program (China Special Fund: CH080253): GPS radio occultation data processing and assimilation system for weather forecast (2009) III • Australia International Science Linkage Program Competitive Grant Scheme with USA (CG130127): Assimilation of GPS radio occultation data with numerical weather prediction system for climate monitoring (2008 - 2010) • Australia Research Council Linkage Program (LP0883288): Satellite-based radio occultation for atmospheric sounding, weather forecasting and climate monitoring in the Australian region ($1.6 million, 2008 - 2010) • Australian Bureau of Meteorology Strategic Investment Fund: Investigation of atmosphere and climate based on GPS, Galileo and LEO-LEO radio occultation in Australia (2007 - 2008) This research work is dedicated to my beloved parents (Weiguo Fu and Qiaolin Wang), my lovely wife Yanxi Zhou, and my relatives and friends for their understanding and full support that have kept me moving forward. IV Abstract The Earth’s atmosphere is critical to the environment and to life on Earth. Studying the atmosphere plays an important role in many scientific areas and in particular meteorology. However, observing the atmosphere is a challenging task due to its dynamic nature and complexity of its processes. Current station-based observations and satellite remote sensing techniques have different limitations (e.g. limited coverage, and/or limited resolution). Better observation techniques are desirable to capture the detailed status and processes of the atmosphere properly. Recent developments of the Global Navigation Satellite Systems (GNSS) radio occultation (RO) technique have offered an exciting potential for meteorological research. This emerging technique, using radio signals between the Low Earth Orbit (LEO) and GNSS satellites, probes the Earth's atmosphere and ionosphere from space. Through a number of experimental missions and related studies since 1995, GNSS RO has demonstrated many advantages over other atmospheric observation methods. The information delivered by GNSS RO missions has advanced many meteorological and climate related studies as well as applications, such as numerical weather prediction analysis, tropopause studies, ionosphere and space weather conditions. 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. A review of past and present GNSS RO missions confirms the potential for Australian meteorology with better observations at a lower cost. The next generation GNSS RO missions, with the advantage of the multiple systems, will have significant 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. V Detailed statistic analyses are carried out to assess the atmospheric profiles derived from the Global Positioning System (GPS) RO against other atmospheric measurements and modelled data. Four studies apply suitable statistics 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. Climatology will benefit significantly from the high accuracy, high resolution and consistent information obtained from the GNSS RO technique. This thesis presents two 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. Examining the tropopause structure requires detailed vertical atmospheric profile information and this is difficult in some situations. The GPS RO technique can retrieve high vertical resolution atmospheric profiles with a uniformed global coverage. The other study is designed to investigate the tropopause over the Australasian region using GPS FORMOSAT-3/COSMIC RO temperature profiles. The FORMOSAT-3/COSMIC RO data provide the best vertical resolution of upper air 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. VI Table of Contents Chapter 1 Introduction..............................................................................1 1.1 Background .....................................................................................................1 1.2 Research motivation and objectives................................................................4 1.3 Research methodology and contributions.......................................................6 1.4 Thesis outline ..................................................................................................8 Chapter 2 GNSS and Earth Atmospheric Observations........................11 2.1 Introduction...................................................................................................11 2.2 Earth atmospheric observations ....................................................................11 2.2.1 Radiosonde observations........................................................................12 2.2.2 Space-based observations.......................................................................14 2.3 GNSS and atmosphere ..................................................................................17 2.3.1 Fundamentals of satellite positioning technique ....................................17 2.3.2 GNSS signals and the atmospheric effects.............................................19 2.4 GNSS-based atmospheric observations ........................................................23 2.4.1 Ground-based GPS water vapour observations......................................23
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