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

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

3. 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

5. 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

6. 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

7. 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.

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

9. Radial pattern of 13Mhz from ship

10. 22 Jan 07, 1700GMT

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

12. 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

13. 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

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

15. Ship Track and HF Radar Location

16. Scatterplots

17. Scatterplots

18. 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

19. 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

20. 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

21. 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
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