PRECISE HYDRODYNAMIC LEVELLING USING PRESSURE GAUGES WITH APPLICATION TO IMPROVEMENT OF THE ESTONIAN NATIONAL LEVELLING NETWORK RÕHUANDURITEL PÕHINEV TÄPNE HÜDRODÜNAAMILINE LOODIMINE RAKENDATUNA EESTI RIIKLIKU KÕRGUSVÕRGU REKONSTRUEERIMISEL AIVE LIIBUSK A Thesis for applying for the degree of Doctor of Philosophy in Geodesy Väitekiri filosoofiadoktori kraadi taotlemiseks geodeesia erialal Tartu 2013 EESTI MAAÜLIKOOL ESTONIAN UNIVERSITY OF LIFE SCIENCES PRECISE HYDRODYNAMIC LEVELLING USING PRESSURE GAUGES WITH APPLICATION TO IMPROVEMENT OF THE ESTONIAN NATIONAL LEVELLING NETWORK RÕHUANDURITEL PÕHINEV TÄPNE HÜDRODÜNAAMILINE LOODIMINE RAKENDATUNA EESTI RIIKLIKU KÕRGUSVÕRGU REKONSTRUEERIMISEL AIVE LIIBUSK A Thesis for applying for the degree of Doctor of Philosophy in Geodesy Väitekiri fi losoofi adoktori kraadi taotlemiseks geodeesia erialal Tartu 2013 Institute of Forestry and Rural Engineering Estonian University of Life Sciences According to verdict No 27 of March 11, 2013, the PhD Committee for Engineering Science of the Estonian University of Life Sciences has accepted this thesis for the defence of degree of Doctor of Philosophy in Geodesy. Opponent: Prof. Markku Poutanen Department of Geodesy and Geodynamics Finnish Geodetic Institute Supervisors: Prof. Artu Ellmann Faculty of Civil Engineering Tallinn University of Technology Ass. Prof. Harli Jürgenson Institute of Forestry and Rural Engineering Estonian University of Life Sciences Language editor: Marguerite Oetjen Defence of this thesis: Estonian University of Life Sciences, room 1A5, Kreutzwaldi 5, Tartu on April 22, 2013 at 12:00. Publication of the thesis is supported by Estonian University of Life Sciences and Doctoral School in the Field of Building and Environmental Engineering. © Aive Liibusk 2013 ISBN 978-9949-484-79-9 (trükis) ISBN 978-9949-484-80-5 (pdf) CONTENTS LIST OF FIGURES ..................................................................................... 8 LIST OF TABLES ...................................................................................... 10 LIST OF PUBLICATIONS .......................................................................11 LIST OF ABBREVIATIONS ................................................................. 12 INTRODUCTION ......................................................................................14 1. REVIEW OF LEVELLING METHODS AND SPECIFICS OF THE STUDY AREA ...........................................18 1.1. Methods of across-water levelling .............................................18 1.1.1. GNSS-levelling ..................................................................18 1.1.2. Geometric levelling ..........................................................19 1.1.3. Trigonometric levelling ....................................................20 1.1.4. Hydrostatic levelling .........................................................21 1.1.5. Hydrodynamic levelling ...................................................22 1.1.6. Summary of achieved accuracies of across-water levelling ...............................................................................23 1.2. The Estonian National Levelling Network .............................24 1.2.1. Historical across-water levellings in Estonia ................25 1.2.2. Opportunities for across-water levelling in the modern Estonian National Levelling Network ...........27 2. AIMS OF THE STUDY ...................................................................30 3. EQUIPMENT, METHOD AND DATA PROCESSING .........32 3.1. Equipment for sea level observations .......................................32 3.1.1. Staff gauges ........................................................................32 3.1.2. Float-based gauges ............................................................33 3.1.2.1. Stilling-well gauges .............................................33 3.1.2.2. Modern geodetic instruments, adapted for sea level observations ....................34 3.1.3. Automatic tide gauges ......................................................36 3.1.3.1. Acoustic gauges ...................................................36 3.1.3.2. Radar gauges ........................................................37 3.1.3.3. Pressure gauges ...................................................38 3.1.4. Conclusions on usable equipment ..................................41 3.2. Principles of hydrodynamic levelling ........................................43 5 3.3. Specifi cs of the study area ..........................................................46 3.3.1. Considerations of the sea surface topography of the Väinameri Basin ....................................................47 3.3.2. Determination of height differences in the study area ............................................................................53 3.4. Water level registration with piezoresistive and capacitive pressure gauges ..........................................................54 3.5. Set up of pressure gauges and data acquisition .......................56 3.6. Processing sea level series ...........................................................62 3.6.1. Detecting time-dependent drift .....................................64 3.6.1.1. Control readings and estimating parameters of drift trend ...................................65 3.6.1.2. Computing the drift-corrected data .................70 3.6.1.3. Reliability of the estimated drift corrections ..70 3.6.2. Filtering of sea level series ...............................................76 4. RESULTS, THEIR VERIFICATIONS AND DISCUSSION ..78 4.1. Results of pressure gauge-based hydrodynamic levelling ......78 4.2. Internal verifi cations of the annual hydrodynamic levelling results .............................................................................80 4.2.1. Short-term “ice-tamed” sea level observations ............80 4.2.1.1. “Ice-tamed” observations in February 2011 ...81 4.2.1.2. “Ice-tamed” observations in March 2012 .......86 4.2.2. Hydrodynamic levelling with “thinned” data ..............87 4.3. External verifi cations of the annual hydrodynamic levelling results .............................................................................89 4.3.1. Hydrostatic levelling for verifying across-water hydrodynamic levelling results .......................................90 4.3.2. Geometric levelling for verifying land-connected hydrodynamic levelling results .......................................95 4.3.3. GNSS-levelling for verifying across-water and land- connected hydrodynamic levelling results ....................96 4.4. Combining the hydrodynamic and spirit levelling results into a closed loop .........................................................................99 4.5. Conclusions and discussion on verifi cations .........................101 5. SUMMARY AND CONCLUSIONS ............................................106 6 REFERENCES ..........................................................................................112 APPENDICES............................................................................................121 APPENDIX A. Transformation the acquired raw pressure gauge data to the same (arbitrary) height system ................................................................122 APPENDIX B. Historical staff gauge series for hydrodynamic levelling ................................................125 APPENDIX C. Compilation of empirical land uplift WEst12LU model over the West-Estonian Archipelago ............128 APPENDIX D. Profi le-wise verifi cations of gravimetric GRAV-GEOID2011 model over marine areas .......132 SUMMARY IN ESTONIAN ..................................................................145 ACKNOWLEDGEMENTS....................................................................150 PUBLICATIONS .......................................................................................151 CURRICULUM VITAE.......................................................................... 223 ELULOOKIRJELDUS ........................................................................... 225 7 LIST OF FIGURES Figure 1. Layout of the Estonia National Levelling Network in 2012 25 Figure 2. Locations of installed pressure gauges and connecting levelling lines around the Väinameri Basin 27 Figure 3. Basic structure of a stilling-well system (modifi ed from Pugh 1987) 34 Figure 4. Prism on a fl oat tracked by an Autolock total station 35 Figure 5. Schema of a bubbler gauge (modifi ed from Pugh 1987) 39 Figure 6. Principles of hydrodynamic levelling 43 Figure 7. GNSS-derived mean sea surface topography (SST) in the Väinameri Basin in 2010 and 2011 52 Figure 8. Pressure sensors Keller 36XW and Keller 46X 57 Figure 9. Typical set up of a pressure gauge station used in this study 60 Figure 10. Differences between the readings of two Keller 46X sensors (upper minus lower) in Sõru, Triigi and Kuivastu 63 Figure 11. The differences between the readings of pressure sensor and staff gauge and drift trends 68 Figure 12. Estimated daily height differences (∆H) of across-water CPs at the Virtsu–Kuivastu, Triigi–Sõru and Heltermaa–Rohuküla sections 72 Figure 13. Estimated daily height differences (∆H) of land- connected CPs at the Rohuküla–Virtsu, Kuivastu–Triigi and Sõru–Heltermaa sections 73 Figure 14. A sample of the ferry-induced data jumps in the Virtsu sea level series on July 5, 2010 76 Figure 15. Ice conditions in the Väinameri and nearby areas on February 23, 2011 and March 4, 2012 as seen on MODIS satellite images 81 Figure 16. Sea level observations by electronic distance