Satellite Altimetry and Earth Sciences

Satellite Altimetry and Earth Sciences

Satellite Altimetry and Earth Sciences

This is Volume 69 in the INTERNATIONAL GEOPHYSICS SERIES A series of monographs and textbooks Edited by RENATA DMOWSKA, JAMES R. HOLTON, and H. THOMAS ROSSBY A complete list of books in this series appears on the IGS Website, http://www.academicpress.com/igs

Satellite Altimetry and Earth Sciences A Handbook of Techniques and Applications Edited by Lee-Lueng Fu Jet Propulsion Laboratory California Institute of Technology Pasadena, California Anny Cazenave Laboratoire d'etudes en Geophysique et Oceanographie Spatiates Centre National d'etudes Spatiates Toulouse, France ACADEM IC PRESS San Diego A Horcourt Science ond Technology Compony San Francisco New York Boston London Sydney Tokyo

This book is printed on acid-free paper. Copyright Cc~ 2001 by ACADEMIC PRESS All Rights Reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording, or any information storage and retrieval system, without permission in writing from the publisher. Requests for permission to make copies of any part of the work should be mailed to: Permissions Department, Harcourt, Inc., 6277 Sea Harbor Drive, Orlando, Florida 32887-6777 Explicit permission from Academic Press is not required to reproduce a maximum of two figures or tables from an Academic Press chapter in another scientific or research publication provided that the material has not been credited to another source and that full credit to the Academic Press chapter is given. Academic Press A Harcourt Sctence and Technology Company 525 B Street, Suite 1900, San Diego, California 92101-4495, USA http://www, acad emi cpress, com Academic Press Harcourt Place, 32 Jamestown Road, London NW1 7BY, UK http://www, academi cpres s. com Library of Congress Catalog Card Number: 00-102572 International Standard Book Number: 0-12-269545-3 PRINTED IN THE UNITED STATES OF AMERICA 00 01 02 03 04 05 EB 9 8 7 6 5 4 3 2 1

Contents Contributors Preface xi ix 1 Satellite Altimetry DUDLEY B. CHELTON, JOHN C. RIES, BRUCE J. HAINES, LEE-LUENG FU, AND PHILIP S. CALLAHAN 1. Introduction 1 2. Radar Measurement Principles 4 2.1. Normalized Radar Cross Section 4 2.2. Ocean Surface Reflectivity 6 2.3. Atmospheric Attenuation 7 2.4. Two-Way Travel Time 11 3. Range Estimation 37 3.1. Atmospheric Refraction 37 3.2. Sea-State Effects 57 4. Precision Orbit Determination 64 4.1. The Orbit Determination Concept 66 4.2. Precision Satellite Tracking Systems 73 4.3. Orbit Estimation 79 4.4. Performance Assessment 82 4.5. Future Prospects 85 5. Geophysical Effects on the Sea Surface Topography 86 5.1. GeoidUndulations 86 5.2. Dynamic Sea-Surface Height 87 5.3. Ocean Tides 88 5.4. Atmospheric Pressure Loading 90 5.5. Aliased BarotropicMotion 91 6. Significant Wave Height Estimation 92 6.1. Significant Wave-Height Algorithms 92 6.2. Significant Wave Height Measurement Accuracy 93 7. Wind-Speed Estimation 95 7.1. Wind-Speed ModelFunctions 95 7.2. Wind Speed Measurement Accuracy 99 8. TOPEX/POSEIDON Mission Design and Performance 99 8.1. Orbit Considerations and Altimeter Sampling Patterns 99 8.2. Calibration and Validation 117 8.3. Measurement Performance 119 9. Outlook for Future Altimeter Missions 119 Acknowledgments 121 References 122 2 Large-Scale Ocean Circulation LEE-LUENG FU AND DUDLEY B. CHELTON 1. Introduction 133 2. The Ocean General Circulation 134 3. The Temporal Variability 138 3.1. Buoyancy-Forcing and the Heat Budget of the Ocean 140 3.2. Atmospheric Pressure Forcing 141 3.3. Wind Forcing 142 3.4. Baroclinic Rossby Waves 145 3.5. The Relation Between Sea Level and Subsurface Variability 158 3.6. The Annual Cycle 161 3.7. InterannualVariability 162 4. Conclusions 163 Acknowledgments 165 References 165

vi CONTENTS 3 Ocean Currents and Eddies P. Y. LE TRAON AND R. MORROW 1. Introduction 171 2. Altimeter Data Processing for Mesoscale Studies 173 2.1. Ocean Signal Extraction 173 2.2. Mapping and Merging of Multiple Altimeter Missions 174 2.3. Surface Geostrophic Velocity Calculations 174 2.4. Sampling Issues 176 3. Ocean Currents 177 3.1. Estimating the Absolute Velocities and Transports from Altimetry 178 3.2. Western Boundary Currents 180 3.3. Eastern Boundary Currents 186 3.4. Open Ocean Currents 189 3.5. Semi-Enclosed Seas 195 4. Mesoscale Eddies 198 4.1. Global Statistical Description 199 4.2. Seasonal Variations of Mesoscale Variability Intensity 200 4.3. Space and Time Scales of Mesoscale Variability 201 4.4. Frequency/Wavenumber Spectral Analysis 203 4.5. Comparison with Eddy-Resolving Models 206 4.6. Eddy Dynamics 206 5. Conclusions 209 Acknowledgments 210 References 210 5 Data Assimilation by Models ICHIRO FUKUMORI 1. Introduction 237 2. Examples and Merits of Data Assimilation 238 3. Data Assimilation as an Inverse Problem 243 4. Assimilation Methodologies 245 4.1. Inverse Methods 245 4.2. Overview of Assimilation Methods 246 4.3. Adjoint Method 246 4.4. Representer Method 247 4.5. Kalman Filter and Optimal Smoother 248 4.6. Model Green's Function 249 4.7. Optimal Interpolation 249 4.8. Three-Dimensional Variation Method 250 4.9. Direct Insertion 250 4.10.Nudging 251 4.11.Summary and Recommendation 251 5. Practical Issues of Assimilation 252 5.1. Weights, A Priori Uncertainties, and Extrapolation 252 5.2. Verification and the Goodness of Estimates 5.3. Observability 259 5.4. Mean Sea Level 260 6. Summary and Outlook 261 Acknowledgments 262 References 262 257 4 Tropical Ocean Variability JOEL PICAUT AND ANTONIO J. BUSALACCHI 1. Introduction 217 2. Tropical Pacific 218 2.1. Sea-level Validation 218 2.2. Altimetry-derived Surface Current 221 2.3. Evidence of Equatorial Waves 221 2.4. Testing Theories of ENSO, Improving Its Prediction 225 2.5. Changes of Mass, Heat and Salt of the Upper Ocean 226 2.6. High-frequency Oscillations 227 3. Indian Ocean 227 4. Tropical Atlantic 229 5. Conclusion 232 Acknowledgments 233 References 233 6 Ocean Tides C. LE PROVOST 1. Introduction 267 2. Mathematical Representation of Ocean Tides 268 2.1. The Harmonic Expansion 268 2.2. The Response Formalism 268 2.3. The Orthotide Formalism 269 3. Status Before High-Precision Satellite Altimetry 270 3.1. In Situ Observations 270 3.2. Hydrodynamic Numerical Modeling 270 3.3. Modeling With Data Assimilation 272 4. Methodologies for Extracting Ocean Tides from Altimetry 272 4.1. Tidal Aliasing in Altimeter Data 273 4.2. Methods for Estimating Ocean Tides from Satellite Altimetry 275

CONTENTS vii 5. The Semi-Diurnal and Diurnal Tides over the Deep Ocean 277 5.1. Characteristics of the Ocean Tides at the Global Scale 277 5.2. Coherency and Accuracy Assessment 279 6. The Long Period Ocean Tides 287 7. Internal Tides 291 7.1. Methodology for Internal Tide Extraction from Satellite Data 291 7.2. Recent Results on Internal Tides from Satellite Altimetry 292 8. The Tides over Shallow Waters 293 8.1. Nonlinear Constituents Solutions from Altimetry 293 8.2. Improving Shallow-water Tide Solution Through Assimilation 294 9. Tidal Energetics and Satellite Altimetry 294 9.1. Dissipation Through Bottom Friction 295 9.2. Tidal Fluxes 295 9.3. Internal Tide Dissipation 297 10.Applications 297 10.1.Earth Rotation 298 10.2.Tidal Loading 298 10.3.Tidal Currents 298 10.4.Tides and Coastal Engineering 300 11.Conclusions 300 Acknowledgments 301 References 301 7 Ocean Surface Waves J.-M. LEFI~VRE AND P. D. COTTON 1. Introduction 305 2. Wave Modeling and Altimetry 306 2.1. NumericalWave Prediction 306 2.2. AltimetricApplications 308 2.3. Operational Data Assimilation 311 2.4. Use of Model Data to Improve Altimetry 315 3. Wave Climate Studies with Altimeter Data 316 3.1. Introduction 316 3.2. The Data 316 3.3. Global Ocean Wave Field 318 3.4. Climate Variability 320 3.5. Summary 326 4. Conclusions 326 5. Glossary 327 Acknowledgments 327 References 327 1. Introduction 329 8 Sea Level Change R. S. NEREM AND G. T. MITCHUM 2. The Tide Gauge Record and its Limitations 330 3. Satellite Altimeter Measurements of Sea-Level Change 332 4. Calibration of Satellite Altimeter Measurements Using Tide Gauge Data 334 5. Detecting Changes in the Rate of Sea-Level Rise 338 6. Global Mean Changes in Sea Level, Sea-Surface Temperature, and Precipitable Water 342 7. Spatial Variations of Sea-Level Change and Sea-Surface Temperature 344 8. Linking Together Different Satellite Altimeter Missions 346 9. Conclusions 347 Acknowledgments 347 References 347 9 Ice Sheet Dynamics and Mass Balance H. JAY ZWALLY AND ANITA C. BRENNER 1. Introduction 351 2. Radar Altimeter Measurement of Ice Sheet Surface Elevations 354 2.1. The Effect of Surface Slope and Undulations 355 2.2. The Effect of Penetration and Sub-surface Volume Scattering 356 2.3. Waveform Shape Fitting and Retracking 357 2.4. Summary of Radar Altimetry Missions Used for Ice Sheet Elevation Studies 359 3. Greenland and Antarctica Ice Sheet Topography 360 3.1. Data Preparation 360 3.2. Gridding Procedure 361 3.3. Accuracy Analysis of Digital Elevation Models 361 4. Ice Surface Slopes and Driving Stresses 362 5. Measurement of Ice Margins 363 6. Surface Elevation Changes and Mass Balance 363 Acknowledgments 367 References 367

viii CONTENTS 10 Applications to Geodesy BYRON D. TAPLEY AND MYUNG-CHAN KIM 1. Introduction 371 2. Mean Sea Surface Mapping 373 2.1. Historical Review 375 2.2. Repeat-Track Averaging 376 2.3. Crossover Adjustment 378 2.4. Weighted Least-Squares Objective Analysis 382 3. Gravity Recovery 386 3.1. Geoid Undulation and Gravity Anomaly 386 3.2. Short-Wavelength Marine Gravity Field 389 3.3. Global Gravity Recovery 391 3.4. Marine GeoidError 392 4. New Frontiers 395 4.1. Time-Varying Gravity Field 395 4.2. Variations in the Geocenter and Earth Rotation Parameters 397 4.3. Roles of Satellite Gravity Data 399 5. Concluding Remarks 403 Acknowledgments 403 References 403 11 Applications to Marine Geophysics ANNY CAZENAVE AND JEAN YVES ROYER 1. Introduction 407 2. Filtering the Long-Wavelength Geoid Signal 408 3. Geoid Anomalies and Isostatic Compensation 408 3.1. Local Compensation in the Long-Wavelength Approximation 409 3.2. Regional Compensation 410 3.3. Admittance Approach 411 4. Mechanical Behavior of Oceanic Plates: Flexure under Seamount Loading 411 5. Thermal Evolution of the Oceanic Lithosphere 413 6. Oceanic Hotspot Swells 416 7. Short and Medium Wavelength Lineations in the Marine Geoid 418 8. Mapping the Seafloor Tectonic Fabric 420 8.1. Fracture Zones 420 8.2. Seamounts 423 8.3. Spreading Ridges 432 9. Conclusions 434 Acknowledgments 435 References 435 12 Bathymetric Estimation DAVID T. SANDWELL AND WALTER H. E SMITH 1. Introduction 441 2. Gravity Anomaly and Sea Surface Slopes 442 2.1. Geoid Height, Vertical Deflection, Gravity Gradient, and Gravity Anomaly 442 3. Limitations of Radar Alitmetry for Gravity Field Recovery 443 4. Forward Models 444 5. Inverse Approaches 445 6. Data Availability and Case Study: Bathymetric Estimation 447 6.1. Results, Verification, and Hypsometry 448 6.2. Effects on Ocean Currents 451 7. Prospects for the Future 452 8. Appendix: Interaction of the Radar Pulse with the Rough Ocean Surface 453 8.1. Beam-Limited Footprint 453 8.2. Pulse-limited Footprint 454 8.3. Significant Wave Height 454 8.4. Modeling the Return Waveform 456 References 456 Index 459