ISBN 4-274-9378-8
ISBN 1 58603 076 0 (IOS Press)
Chapter 1: Introduction Chapter 2: Basic Concepts: A Quick Tour of VLBI Chapter 3: Data Processing Techniques Chapter 4: Data Analysis Chapter 5: Geodetic VLBI Experiments Chapter 6: Applications of VLBI Techniques Chapter 7: In Conclusion |
The book will be published in June, 2000 by Ohmsha and IOS Press.
Contacts
IOS Press Nieuwe Hemweg 6B 1013 BG Amsterdam The Netherlands Tel:+31-20-688-3355 Fax:+31-20-620-3419 E-mail: market(AT)iospress.nl http://www.iospress.nl |
Ohmsha 3-1 Kanda Nishiki-cho, Chiyoda-ku,Tokyo 101 Japan Tel.+81-3-3233-0641 Fax.+81-3-3233-2426 E-mail: hanbaibu(AT)ohmsha.co.jp https://www.ohmsha.co.jp/index_e.htm |
In October 1896, one year after the success of Marconi's wireless telegraphy experiments, Japan started research into wireless telegraphy at the Electrical Technical Laboratory of the Ministry of Communications. The following year, Mr. Matsunosuke Matsushiro found success in his wireless telegraphy experiments. The Radio Research Laboratories, Ministry of Posts and Telecommunications, was established in 1952 after some reorganization of the laboratories researching radio communication technology. The Radio Research Laboratories was renamed the Communications Research Laboratory in 1988 to reflect the change in the environment for research following the privatization of the Nippon Telegraph and Telephone Corporation in Japan.
To celebrate 100 years of radio communications, we have spent several years at the Communications Research Laboratory planning and preparing to publish in book from the results of the research so far conducted. Entitled the "Wave Summit Course", it will contain a series of papers on various aspects of radio communications technology and is aimed at students of both the senior and graduate levels, that is, the generation of scientists who will lead the way in the 21st century.
Now the time for publication has arrived. This series consists of seven volumes: 'Satellite Communications', 'Very Long Baseline Interferometer', 'Science of Space Environment', 'Modern Millimeter-Wave Technologies', 'Digital Broadcasting', 'Mobile Communications', and 'Global Environment Remote Sensing'. We hope that these volumes will be widely read as useful guides to the different fields in which radio waves are used.
Finally, I would like to extend my deep gratitude to all those involved in enabling this project to come to fruition, including the authors, editors, and successive Director-Generals of the CRL and chairpersons of the publications committee, and of course to Ohmsha, Ltd. for their untiring assistance and encouragement.
Dr. Takashi Iida Director-General Communications Research Laboratory Ministry of Posts and Telecommunications |
This text, entitled "Very Long Baseline Interferometer", celebrates the 100th anniversary of the discovery of the wireless telegraph, and is one of the texts in the "Wave Summit Course" published by the Communications Research Laboratory (CRL), Ministry of Posts and Telecommunications. The material covered in this text is presented in as systematic a manner as is possible, and although aimed specifically for the student of VLBI, it should also be suitable for engineering school and graduate-level students as well.
VLBI is an acronym for Very Long Baseline Interferometer, and can be roughly divided into two areas of application. The first area is in geodesy, which is covered in considerable detail in the text. The second area is in astrometry, or radio astronomy, which is only briefly treated in this text.
Many people probably relate geodesy and land surveying more with geology and geography than with space-based measuring techniques; and at least up through the first half of the 20th century, geodesy was largely based on knowledge in these fields. Surveyors were generally considered as technicians or craftsmen. Modern GPS (Global Positioning Systems) is probably best known for its use in automobile navigation, but such space-based measuring systems have made tremendous advances in the field of geodesy as well.
In a 1996 speech announcing the United States' policy regarding GPS, the US Vice President, Albert Gore, boasted to the world that, in addition to the Internet, the US had achieved a level of technology in space-based measuring systems far superior to any other country on earth. Given Japan's present status in the high-tech field of modern geodesy, it appears that we have been relegated to following the US's lead. This is paricularly true with regards to GPS, which can be considered as a large engineering conglomerate consisting of both space and terrestrial systems. Such a project requires large financial support, but if not correctly evaluated and prioritized, simply having the correct scientific knowledge will not necessarily produce successful results. The same can be said for VLBI: at first glance it is easy to mistake the motives and outcomes of research of being for a scientific project because it deals primarily with the sciences of astronomy and geodesy. As with GPS, VLBI should also be considered as a project yielding superb scientific results because of a well-financed, flawlessly operated engineering system which allows the melding of hardware and software technologies.
The CRL has provided an environment where hardware and software can be properly evaluated from an engineering standpoint, and scientists and engineers have cooperated in the development of the world's most advanced VLBI technologies.
The word "geodesy" in Japanese is a term composed of the words, measurement, earth, and studies. The word itself strongly embodies the engineering elements of metering distances and determination of precision values. The study you are about to embark on in space-based surveying encompasses VLBI techniques in this case, but as its name implies, is also a new world of science that combines hardware and software to create a megatechnology. Radio wave and microwave technology form the core of the VLBI system. One can thus immediately see that the late marriage of VLBI and wireless communications technology which is over 100 years old really means that VLBI has a connection to the past, present, and to the future.
The authors of this text are members of the research staff at the Communications Research Laboratory. We have also written this book from the perspective of a group of scientists who, until reaching the university level had never had the opportunity to utilize such technologies as we have available to us now. Consequently, we consider ourselves to be members of a group whose primary purpose is to determine how to best realize scientific results from the technology-heavy equipment found in VLBI systems.
The most notable results obtained by VLBI so far has been the global-scale measuring of the movements of the tectonic plates which cover the surface of the earth. Details of this achievement are discussed in the text, but the primary focus of the material covered here remains an investigation of how VLBI can conduct these measurements with such a high level of precision. The text also explains how the various aspects of system hardware, software, and data analysis techniques can be effectively combined to yield a measurement accuracy that is four orders in magnitude better than conventional surveying techniques. VLBI requires knowledge in many areas of science and engineering. To the students of this text: as you carefully study the processes by which these highly precise measurements are achieved, you should gain an appreciation of how each process relates to the various areas of engineering and science. We also believe that the text will be very useful to researchers having prior knowledge of GPS techniques.
If this text proves useful in overcoming to some degree the huge advantage that the US presently enjoys in GPS and other measuring technologies, we will be gratified beyond our expectations.
Finally, the authors wish to express our gratitude to Mr. Wayne Hughes, the translator of this text.
May 2000 Fujinobu Takahashi |
Chapter 1 Introduction | |||
1.1 The Birth of Radio Astronomy | 1 | ||
1.2 The Concepts of Radio Interferometry | 3 | ||
1.3 The Evolution of the Atomic Clock | 4 | ||
1.4 Developments in Large-Scale Antenna Technology | 6 | ||
1.5 Advances in Signal Processing Technology | 7 | ||
1.6 The Advent of Geodetic VLBI | 9 | ||
1.7 Chapter Outlines | 11 | ||
. Chapter Questions | 12 | ||
. Chapter References | 12 | ||
Chapter 2 Basic Concepts: A Quick Tour of VLBI | |||
| 2.1 The Basic Principles of Radio Interferometry | 13 | |
2.2 Galactic Radio Sources and Coordinate Systems | 15 | ||
2.3 Observational Coordinate Systems | 17 | ||
2.3.1 Surveying the Earth's Shape from Outside the Solar System | 18 | ||
2.4 Propagation Delays | 21 | ||
| 2.4.1 Atmospheric Propagation Delay | 22 | |
2.4.2 Solar and Planetary Effects | 23 | ||
2.5 Basic Principles of VLBI | 23 | ||
2.6 VLBI System Components: A Historical Sketch | 27 | ||
2.7 VLBI Observations | 33 | ||
2.7.1 Observation Equipment | 33 | ||
2.7.2 Observation Schedules | 37 | ||
2.8 Data Processing Flow in Geodetic VLBI | 40 | ||
2.9 Collaboration in VLBI Experiments | 41 | ||
. Chapter Questions | 44 | ||
. Chapter References | 44 | ||
Chapter 3 Data Processing Techniques | |||
| 3.1 The Fourier Transform and Applications | 45 | |
| 3.1.1 Defining the Fourier Transform | 46 | |
3.1.2 Time Shifts and Fourier Transforms | 47 | ||
3.1.3 Correlation Theorem | 47 | ||
3.1.4 The Convolution Theorem | 49 | ||
3.2 A VLBI Equivalent Signal Model | 51 | ||
3.3 One-Bit Sampling | 54 | ||
3.4 Maximum Likelihood Estimation of Delay | 57 | ||
| 3.4.1 Maximum Likelihood Estimation Principle and Least- Squares Method | 57 | |
3.4.2 Cross-Correlation as the Maximum Likelihood Esti- mation of Delay: A Time-Domain Approach | 59 | ||
3.4.3 Cross-Correlation as the Maximum Likelihood Esti- mation of Delay: A Frequency-Domain Approach | 62 | ||
3.5 Cross-Correlation Function in VLBI | 65 | ||
| 3.5.1 Cross-Correlation Function (without frequency conversion) | 65 | |
3.5.2 Cross-Correlation Function of the Video Signal | 67 | ||
3.6 Correlator Processing | 70 | ||
| 3.6.1 Correlation Processing Principles | 70 | |
3.6.2 Delay Tracking | 72 | ||
3.6.3 Fringe Stopping | 75 | ||
3.6.4 Bit Shifts and 90-degree Phase Jumps | 79 | ||
3.6.5 Fractional Bit Correction | 83 | ||
3.6.6 Phase Calibration Signal Detection | 84 | ||
3.7 Precise Determination of Delay and Delay Rates | 85 | ||
| 3.7.1 Normalizing Correlator Output | 86 | |
3.7.2 Coarse Delay Search | 88 | ||
3.7.3 Precise Delay Search using Bandwidth Synthesis | 91 | ||
3.7.4 Ambiguities in Bandwidth Synthesis | 93 | ||
3.8 Verification of VLBI Measurement Precision | 96 | ||
| 3.8.1 Scattering and Bias of Measurement Values | 96 | |
3.8.2 Signal-to-Noise Analysis | 96 | ||
3.8.3 Theoretical Delay Errors | 100 | ||
3.8.4 Error Verification using Independent Correlation Systems | 104 | ||
3.9 Real-Time VLBI | 105 | ||
. Chapter Questions | 107 | ||
. Chaptert References | 107 | ||
Chapter 4 Data Analysis | |||
| 4.1 Overview of Data Analysis | 109 | |
4.2 VLBI Reference Frames | 114 | ||
| 4.2.1 Inertial Reference Frame of the Solar System | 114 | |
4.2.2 Terrestrial Reference Frame | 116 | ||
4.2.3 Time Systems | 118 | ||
4.3 The Physical Models | 119 | ||
| 4.3.1 The Earth's Rotation | 119 | |
4.3.2 Propagation Delay Corrections | 128 | ||
4.3.3 Tidal Corrections | 132 | ||
4.3.4 Relativistic Effects | 134 | ||
4.3.5 Other Physical Effects | 135 | ||
4.4 Estimating Parameters | 138 | ||
4.5 Analytical Methods | 139 | ||
| 4.5.1 Analysis Procedures | 139 | |
4.5.2 Kalman Filter Estimations | 142 | ||
4.5.3 Analysis Procedures | 144 | ||
4.6 VLBI Errors | 147 | ||
| 4.6.1 Observation Errors | 147 | |
4.6.2 Errors of Estimated Values | 149 | ||
4.7 Improving Analysis Procedures | 150 | ||
. Chapter Questions | 151 | ||
. Chapter References | 151 | ||
Chapter 5 Geodetic VLBI Experiments | |||
| 5.1 The Japanese Geodetic Coordinate System | 155 | |
5.2 Plate Tectonics and Earthquakes | 158 | ||
5.3 Measuring Plate Motions | 161 | ||
5.4 Crustal Deformations near Plate Boundaries | 164 | ||
5.5 The Himalayan Collision Zone and the Japan-China Converging Zone | 165 | ||
5.6 Plate Motion near Japan | 166 | ||
5.7 VLBI Experiments in Japan | 168 | ||
5.8 VLBI Experiments in Antarctica | 171 | ||
5.9 Earth Rotation | 172 | ||
| 5.9.1 Earth Rotation Observations | 172 | |
5.9.2 Results of Earth Rotation Observations | 173 | ||
5.10 Other Experiments | 178 | ||
. Chapter Questions | 179 | ||
. Chapter References | 179 | ||
Chapter 6 Applications of VLBI Techniques | |||
| 6.1 Radio Astronomy | 181 | |
| 6.1.1 Determining Radio Source Positions | 181 | |
6.1.2 Radio Source Structures | 186 | ||
6.2 Precise Measurements of Earth Rotation | 191 | ||
| 6.2.1 Measuring Polar Motions and Fluctuations in Earth Rotation | 191 | |
6.2.2 Fluctuations in Earth Rotation Speed and Atmospheric Angular Momentum | 193 | ||
6.3 Regional Deformation Monitoring System for the Tokyo Metropolitan Area | 195 | ||
| 6.3.1 Geographical Locations of Observation Stations | 196 | |
6.3.2 Observation System | 197 | ||
6.3.3 Automation of Data Analysis | 203 | ||
6.4 Deep-Space Measurements | 207 | ||
6.5 Applications in Ionospheric Measurements | 208 | ||
| 6.5.1 Correcting for Ionospheric Delay | 208 | |
6.5.2 Using Least-Squares Estimation to Determine Total Electron Content of the Ionosphere | 212 | ||
. Chapter Questions | 216 | ||
. Chapter References | 216 | ||
Chapter 7 In Conclusion | |||
| 7.1 The Transition from Centimeter Accuracies to Millimeter Accuracies | 219 | |
7.2 Beyond the Earth | 220 | ||
Addendum | |||
| Table 1 Wahr Nutation Model Coefficients | 221 | |
Table 2 Yoder UT1 Earth Tides Correction Coefficients | 223 | ||
Table 3 Dickman UT1 Earth Tides Correction Coefficients | 224 | ||
Table 4 VLBI Station Positions in the ITRF Coordinate Frame | 226 | ||
Table 5 Selected Radio source Positions for VLBI Observations | 228 | ||
Answers to Chapter Questions | 229 | ||
Postscript | 234 | ||
Author's Profile | 235 | ||
Index | 237 |