OC3570 Project Winter 2007 A COMPARISON OF COASTAL CURRENTS USING LAND BASED HF RADAR AND SHIP BOARD ADCP OBSERVATIONS LCDR Steve Wall, RAN

Scope Introduction Background Method Results Conclusions Discussion HF groundwave current measurement ADCP measurement Method Results Conclusions Discussion

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

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

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

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.

COMM, FORT , MONT measured Radial patterns Ideal vs measured Santa Cruz Moss Landing Pt Pinos NPGS BIGC, PESC, SCRZ Ideal COMM, FORT , MONT measured

Radial pattern of 13Mhz from ship

22 Jan 07, 1700GMT

Background ADCP Ship’s logs Doppler shift Considered standard in this comparison Depth and range binning

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

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

MATLAB Load RDL mfile Processvel mfile Data bin mfile Compare mfile Stats mfile

Ship Track and HF Radar Location

Scatterplots

Scatterplots

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

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

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

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