NOAA Technical Report NOS CO-OPS 075 Water Level and Wave Height Estimates at NOAA Tide Stations from Acoustic and Microwave Sensors Microwave water level sensors at La Jolla California. Silver Spring, Maryland June 2014 noaa National Oceanic and Atmospheric Administration U.S. DEPARTMENT OF COMMERCE National Ocean Service Center for Operational Oceanographic Products and Services Center for Operational Oceanographic Products and Services National Ocean Service National Oceanic and Atmospheric Administration U.S. Department of Commerce The National Ocean Service (NOS) Center for Operational Oceanographic Products and Services (CO-OPS) provides the National infrastructure, science, and technical expertise to collect and distribute observations and predictions of water levels and currents to ensure safe, efficient and environmentally sound maritime commerce. The Center provides the set of water level and tidal current products required to support NOS’ Strategic Plan mission requirements, and to assist in providing operational oceanographic data/products required by NOAA’s other Strategic Plan themes. For example, CO-OPS provides data and products required by the National Weather Service to meet its flood and tsunami warning responsibilities. The Center manages the National Water Level Observation Network (NWLON), a national network of Physical Oceanographic Real-Time Systems (PORTS®) in major U. S. harbors, and the National Current Observation Program consisting of current surveys in near shore and coastal areas utilizing bottom mounted platforms, subsurface buoys, horizontal sensors and quick response real time buoys. The Center establishes standards for the collection and processing of water level and current data; collects and documents user requirements which serve as the foundation for all resulting program activities; designs new and/or improved oceanographic observing systems; designs software to improve CO-OPS’ data processing capabilities; maintains and operates oceanographic observing systems; performs operational data analysis/quality control; and produces/disseminates oceanographic products. NOAA Technical Report NOS CO-OPS 075 Water Level and Wave Height Estimates at NOAA Tide Stations from Acoustic and Microwave Sensors Joseph Park Robert Heitsenrether William V. Sweet June 2014 U.S.DEPARTMENT OF COMMERCE Penny Pritzker, Secretary National Oceanic and Atmospheric Administration Dr. Kathryn Sullivan, NOAA Administrator and Under Secretary of Commerce for Oceans and Atmosphere National Ocean Service Dr. Holly Bamford, Assistant Administrator Center for Operational Oceanographic Products and Services Richard Edwing, Director NOTICE Mention of a commercial company or product does not constitute an endorsement by NOAA. Use of information from this publication for publicity or advertising purposes concerning proprietary products or the tests of such products is not authorized. ii TABLE OF CONTENTS TABLE OF FIGURES ................................................................................................................. iv EXECUTIVE SUMMARY ........................................................................................................ vii INTRODUCTION ........................................................................................................................ 1 Microwave Water Level (MWWL) Phase II Analysis ............................................................. 2 Wave Height and Tide Gauge Standard Deviation ................................................................... 3 Objective ................................................................................................................................... 3 SENSORS ..................................................................................................................................... 4 Acoustic Water Level ............................................................................................................... 4 Microwave Water Level ........................................................................................................... 7 Wave Height and Period ........................................................................................................... 7 DATA ........................................................................................................................................... 8 ACOUSTIC AND MICROWAVE FREQUENCY RESPONSE ............................................... 9 ACOUSTIC TEMPERATURE DEPENDENCE ...................................................................... 11 MECHANICAL FILTER WATER LEVEL DRAW-DOWN .................................................... 13 STANDARD DEVIATION AND SIGNIFICANT WAVE HEIGHT ...................................... 16 DISCUSSION ............................................................................................................................. 19 CONCLUSION ........................................................................................................................... 20 REFERENCES ........................................................................................................................... 21 APPENDIX: Additional Analysis Results .................................................................................. 24 Duck, North Carolina .............................................................................................................. 24 La Jolla, California ................................................................................................................. 30 Lake Worth, Florida ................................................................................................................ 32 Monterey, California ............................................................................................................... 35 ACRONYMS AND SYMBOLS ................................................................................................ 41 iii TABLE OF FIGURES Figure 1. Empirical cumulative distribution functions of Aquatrak Data Quality and Assurance Procedure (DQAP) σ over a period of 1 year at coastal NWLON stations. Empirical cumulative distribution functions of Aquatrak DQAP σ over a period of 1 year at four NWLON stations selected for Phase II analysis. ...................................................................... 2 Figure 2. Schematic diagram of Aquatrak protective well. ..................................................................... 4 Figure 3. Dynamic water level response inside a protective well to surface waves of height H and period T. ........................................................................................................................... 5 Figure 4. Schematic of protective well orifice with a hydraulic current ..................................................... 6 Figure 5. Relationship between water level draw-down in centimeters (Δ h) and surface wave forcing. .................................................................................................................................... 6 Figure 6. Hourly data from Duck, N.C. in April 2012. a) Water level difference between the acoustic and microwave sensors.. ............................................................................................. 8 Figure 7. Power spectral density estimates of 1 Hz water level data from the acoustic and microwave sensors at Duck, N.C. ........................................................................................... 9 Figure 8. PSD of 1 Hz water level data from Lake Worth during September 2013. Resonance of the protective well is presented as a large distortion of the spectral variance centered on a period of 5 seconds. ....................................................................................................... 10 Figure 9. Hourly data and temperature corrections from Duck in April 2012. ...................................... 12 Figure 10. Hourly data and draw-down corrections from Duck in April 2012. ...................................... 13 Figure 11. Probability density functions of range to water difference (acoustic - microwave) for April 2012 at Duck. ............................................................................................................... 14 Figure 12. Probability density functions of range to water level difference (acoustic - microwave) for April 2013 at Duck. ........................................................................................................... 15 Figure 13. a) Hourly significant wave height (Hm0) during a 24 day period in April 2012 at the Duck, N.C. b) Hourly NWLON standard deviations. ........................................................... 16 Figure 14. Hourly significant wave height (Hm0) and estimates of wave height (Hm0) from a linear model of Hm0 regressed onto water level standard deviations (σ) over 24 days of April 2012 at Duck ................................................................................................................. 17 Figure 15. Linear regression of significant wave height (Hm0) onto microwave and acoustic standard deviations shown in Figure 13 over a 24-hour sliding window. ............................ 17 Figure 16. Linear regression of DQAP σ and significant wave height for the acoustic and microwave sensors during April 2013.. .................................................................................. 18 iv Figure 17. PSD and coherence of acoustic and microwave water level data at Duck, N.C. in April 2012.