Measuring Ocean Currents

Measuring Ocean Currents: Tools, Technologies, and Data covers all major aspects of ocean current measurements in view of the implications of ocean currents on changing climate, increasing pollution levels, and offshore engineering activities. Although more than 70% of the Earth is covered by ocean, there is limited information on the countless fine- to large-scale water motions taking place within them. This book fills that information gap as the first work that summarizes the state-of-the-art methods and instruments used for surface, subsurface, and abyssal ocean current measurements.

Readers of this book will find a wealth of information on Lagrangian measurements, horizontal mapping, imaging, Eulerian measurements, and vertical profiling techniques. In addition, the book describes modern technologies for remote measurement of ocean currents and their signatures, including HF Doppler radar systems, satellite-borne sensors, ocean acoustic tomography, and more. Crucial aspects of ocean currents are described in detail as well, including dispersion of effluents discharged into the sea and transport of beneficial materials—as well as environmentally hazardous materials—from one region to another. The book highlights several important practical applications, showing how measurements relate to climate change and pollution levels, how they affect coastal and offshore engineering activities, and how they can aid in tsunami detection.

• Coverage of measurement, mapping and profiling techniques
• Descriptions of technologies for remote measurement of ocean currents and their signatures
• Reviews crucial aspects of ocean currents, including special emphasis on the planet-spanning thermohaline circulation, known as the ocean's "conveyor belt," and its crucial role in climate change

Oceanographers and marine engineers; graduate and Ph.D. students taking courses in oceanography or ocean instrumentation and technology, oceanographic laboratories, public libraries

Acknowledgments

Foreword

Preface

Chapter 1. Oceanic Currents and Their Implications

Abstract

1.1 Oceans’ Thermohaline Conveyor Belt Circulation and Global Climate Change

1.2 Meandering Currents, Eddies, Rings, and Hydrographic Fronts

1.3 Influence of Eddies and Fronts on Fishery and Weather

1.4 Major Current Systems in the World Oceans

1.5 Currents of Different Origins

1.6 Implications of Ocean Currents

References

Chapter 2. The History of Measuring Ocean Currents

Abstract

2.1 Surface Current Measurements

2.2 Subsurface and Abyssal Current Measurements

2.3 Seafloor Boundary Layer Current Measurements

2.4 Vertical Profiling of Horizontal Currents

References

Bibliography

Chapter 3. Lagrangian-Style Surface Current Measurements Through Tracking of Surface Drifters

Abstract

3.1 Radio Buoys

3.2 Limitations of Surface Drifters

References

Bibliography

Chapter 4. Remote Mapping of Sea Surface Currents Using HF Doppler Radar Networks

Abstract

4.1 Crombie’s Discovery

4.2 Peculiarities of Pulse Doppler-Radar Echo Spectra

4.3 Estimation of Sea Surface Current Using the Bragg Resonance Principle

4.4 Depth Extent of Doppler Radar-Based Sea Surface Current Measurements

4.5 Technological Aspects of Doppler Radar-Based Surface Current Mapping

4.6 Experimental Developments

4.7 Instrumentation Aspects

4.8 Radial and Total Vector Currents

4.9 Developments on Operational Scales

4.10 Intercomparison Considerations

4.11 Advantages of Radio-Wave Doppler Radar Measurements

4.12 Round-the-Clock Coast- and Shelf-Observing Role of Doppler Radar

4.13 Detection and Monitoring of Tsunami-Induced Sea Surface-Current Jets at Continental Shelves

References

Bibliography

Chapter 5. Imaging of Seawater Motion Signatures Using Remote Sensors

Abstract

5.1 Aerial Photography in the Visible and Infrared Bands

5.2 Remote Detection by Radiometers

5.3 Active Microwave Radar Imaging of Sea Surface Current Signatures

5.4 Active Microwave Radar Imaging Technologies

5.5 Advances in the Development of SAR Technology

5.6 Detection of Seawater Circulation Features Using RAR and SAR

5.7 Measurement of Sea Surface Currents Using Imaging of Ice Floes

References

Bibliography

Chapter 6. Lagrangian-Style Subsurface Current Measurements Through Tracking of Subsurface Drifters

Abstract

6.1 Surface-Trackable Subsurface Drifters

6.2 Satellite-Recovered Pop-Up Drifters

6.3 Swallow Floats Tracked by Ship-Borne Hydrophones

6.4 Subsurface Floats Transmitting to Moored Acoustic Receivers

6.5 Subsurface Floats Listening to Moored Acoustic Sources

6.6 ALACE: Horizontally Displaced and Vertically Cycling Subsurface Float

6.7 Drifting Profiling Floats (Argo Floats)

References

Bibliography

Chapter 7. Horizontally Integrated Remote Measurements of Ocean Currents Using Acoustic Tomography Techniques

Abstract

7.1 One-Way Tomography

7.2 Two-Way Tomography (Reciprocal Tomography)

7.3 Acoustic Tomographic Measurements from Straits

7.4 Coastal Acoustic Tomography

7.5 River Acoustic Tomography

7.6 Acoustic Tomographic Measurements of Vorticity

7.7 Horizontally Integrated Current Measurements Using Space-Time Acoustic Scintillation Analysis Technique

References

Bibliography

Chapter 8. Eulerian-Style Measurements Incorporating Mechanical Sensors

Abstract

8.1 Eulerian-Style Measurements

8.2 Savonius Rotor Current Meters

8.3 Savonius Rotor and Miniature Vane Vector-Averaging Current Meters

8.4 Propeller Rotor Current Meter (Plessey Current Meter)

8.5 Biaxial Dual Orthogonal Propeller Vector-Measuring Current Meters

8.6 Calibration of Current Meters

8.7 Graphical Methods of Displaying Ocean Current Measurements

8.8 Advantages and Limitations of Mechanical Sensors

References

Bibliography

Chapter 9. Eulerian-Style Measurements Incorporating Nonmechanical Sensors

Abstract

9.1 Electromagnetic Sensors

9.2 Acoustic Travel-Time Difference and Phase Difference Sensors

9.3 Acoustic Doppler Current Meter

References

Bibliography

Chapter 10. Vertical Profiling of Horizontal Currents Using Freely Sinking and Rising Probes

Abstract

10.1 Importance of Vertical Profile Measurements of Ocean Currents

10.2 Technologies Used for Vertical Profile Measurement of Ocean Currents

10.3 Technologies Used for Vertical Profile Measurements of Oceanic Current Shear and Fine Structure

10.4 Technologies Used for Vertical Profile Measurements of Oceanic Current Shear and Microstructure

10.5 Merits and Limitations of Freely Sinking/Rising Unguided Probes

References

Bibliography

Chapter 11. Vertical Profiling of Currents Using Acoustic Doppler Current Profilers

Abstract

11.1 Basic Assumptions and Operational Issues

11.2 Principle of Operation

11.3 Profiling Geometries

11.4 Trawl-Resistant ADP Bottom Mounts

11.5 Horizontal-Facing ADPS

11.6 Subsurface Moored ADPS

11.7 Downward-Facing Shipboard ADPS

11.8 Towed ADPS

11.9 Lowered ADCP (L-ADCP)

11.10 ADPS for Current Profiling and AUV Navigation

11.11 Calibration of ADPS

11.12 Intercomparison and Evaluation

11.13 Merits and Limitations of ADPS

References

Bibliography

Chapter 12. Remote Measurements of Ocean Currents Using Satellite-Borne Altimeters

Abstract

12.1 Oceanic Currents and Associated Features Generated by Sea Surface Slope

12.2 Determination of Seawater Motion from Sea Surface Slope Measurements

12.3 Technological Intricacies in Realizing Satellite Altimetric Measurements

12.4 Correction of Errors in Satellite Altimeter Data

12.5 Evolution of Satellite Altimetry

References

Bibliography

Chapter 13. Conclusions

Abstract

13.1 Progress in Ocean Current Measurement Technologies

13.2 Moored Current Meters and Their Limitations

13.3 Lagrangian Measurements of Surface Currents

13.4 Global Observation of Sea Surface Currents and Their Signatures through Imagery

13.5 Real-Time Two-Dimensional Mapping of Sea Surface Current Vectors

13.6 Global Observation of Surface Geostrophic Currents and Mesoscale Circulation Features

13.7 Current Profile Measurements Using Freely-Moving Sensor Packages and ADPs

13.8 Evolution of Acoustic Tomography: Monitoring Water Flow Structure from Open Ocean, Coastal Waters, and Rivers

13.9 Lagrangian Measurements of Subsurface Currents

13.10 Comprehensive Study of Oceanic Circulation

References

Index