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OC3570 Project Winter 2007 A COMPARISON OF COASTAL CURRENTS USING LAND BASED HF RADAR AND SHIP BOARD ADCP OBSERVATIONS LCDR Steve Wall, RAN
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Scope Introduction Background Method Results Conclusions Discussion
HF groundwave current measurement ADCP measurement Method Results Conclusions Discussion
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Introduction Project as part of OC3570 course
Data from Leg 1 of the cruise 23 to 27 Jan 2007 Moss Landing to San Francisco Original concept was comparing ship based HF radar data with land based Induced errors Not relaible for comparison Adjusted to use ADCP data
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Background HF groundwave measurement
First ‘discovered’ in 1955 by Crombie (NZ) Consistent peak spectral component of backscatter 3-30 MHz (between AM radio and TV) Wavelength, l, ~ 10m
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Ocean waves with l/2 of EM wave are “Bragg” resonant
Other Remote Sensing EM wave Reflected EM wave Ocean waves with l/2 of EM wave are “Bragg” resonant /2 Ocean wave Coherent arrivals Diagram illustrating the effect of coherent (aligned) reflections Backscatter from other surfaces occurs but is much weaker
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Doppler Backscatter Spectrum
Other Remote Sensing Doppler Backscatter Spectrum Independence of first order Bragg scatter depends on the EM wavelength being at least 10x larger than the ocean wave significant wave height Large ocean waves produce saturation (i.e., contamination) from 2nd order backscatter hsat=2/ko 50MHz: 2m 25MHz: 4m 13MHz: 7m 5MHz: 20m From: Stewart, R.H., 1985: Methods of Satellite Oceanography. University of California Press, Berkeley, 360 pp.
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COMM, FORT , MONT measured
Radial patterns Ideal vs measured Santa Cruz Moss Landing Pt Pinos NPGS BIGC, PESC, SCRZ Ideal COMM, FORT , MONT measured
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Radial pattern of 13Mhz from ship
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22 Jan 07, 1700GMT
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Background ADCP Ship’s logs Doppler shift
Considered standard in this comparison Depth and range binning
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Method Obtained radial data from COCAMP website
Dan Atwater Mike Cook Waited upon CODAR data from Chad Welan Obtained ADCP data from Prof Collins How to match up datasets? Different spatial and temporal scales
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MATLAB Programming First challenge Second Challenge Third Challenge
Data from HF groundwave Second Challenge Matching with ship’s position Third Challenge Data from ADCP Fourth Challenge Matching with HF groundwave dataset
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MATLAB Load RDL mfile Processvel mfile Data bin mfile Compare mfile
Stats mfile
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Ship Track and HF Radar Location
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Scatterplots
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Scatterplots
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Conclusions The ADCP data speed values were all greater than HR radar estimations Closest mean value 47% of ADCP (Avg 40%) Lowest RMSE of 13.5 cms-1 (Avg 16) Highest Corr 0.41 (Avg 0.05) PESC The ADCP direction values were generally to the right of the HF radar Closest mean was 97% (Avg 82%) RMSE not good for comparison (going through N) Highest Corr 0.54 (Avg 0.13) SCRZ
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Limitations Comparing 5 minute data to hourly averaged data not a good comparison Different timescales = different processes Different spatial resolutions Point data compared to area averaged data Different depths have different influences Wind driven currents Tidal forcing
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Further Work Comparing tidal flows and wind forcing
Dominant processes Breakdown by time periods or distance More/less accurate in Bay Offshore/Inshore Different depths have different influences Wind driven currents Tidal forcing
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Acknowledgements Prof Paduan Prof Collins LCDR Kyung Cheol Kim, ROKN
Mike Cook Dan Atwater Chad Whelan Prof Collins Prof Guest LCDR Kyung Cheol Kim, ROKN Similar topic 2003 Cruise buddies
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