1. Natalie Laudier Operational Oceanography 13Feb2009
Comparison of Wave Spectra Analyses from Waverider Buoy Data and CDIP Swell Model Predictions
Natalie Laudier
Operational Oceanography
13Feb2009

2. Outline Introduction Methods Results Wave Spectra Sediment Samples
Discussion

3. Carmel River Beach, CA
Purpose: to determine if the CDIP swell model accurately predicts the nearshore wave environment

4. Carmel River Beach, CA Buoy deployed 1927UTC 35.52N, 12.96W
Model W 36.53N
Buoy deployed 1927UTC 35.52N, 12.96W
Recovered at 2105UTC at 35.53N, W
~300m water depth

5. Methods DWR-G Datawell Waverider buoy
GPS three dimensional wave motion (pitch and roll)
Wave periods of 1.6 to 100 seconds
Accuracy of 1cm
Directional: WGS84 reference and has a 1.5deg

6. phase-linear, combined band-pass and single-integrating FIR filter
Waverider Buoy
Heave, North, West
Range
20m to -20m
Accuracy
1cm
Time Period s
Freq Range
0.01Hz-0.64Hz
Direction
0-360deg
1.5deg
Reference
WGS84
Filter
Sampling Freq
2.0Hz
Digital Filtering Type
phase-linear, combined band-pass and single-integrating FIR filter
Data Output Rate
1.28Hz
Sample rate: 1.28Hz
256 samples per segment
Cutoff frequency:
0.64Hz

7. Methods
Filtering: buoy digitally filters with an integrating high-pass filter
Fast Fourier-transform (FFT) used to get the wave height spectrum in the frequency domain
Hanning window used to calculate cross-spectral density
Directional moments a1,a2,b1,b2 calculated from cross-spectral density
Mean direction and directional spreading calculated from moments
Maximum Entropy Method (MEM) to calculate directional energy spectrum

8. Coastal Data Information Program (CDIP) Swell Model
Based on wave refraction and diffraction simulations
Run by SCRIPPS Oceanographic Institute
Wave frequencies > 0.04Hz
No tides or input from local wave generation
Spectra information provided from model
Based on wave observations from an offshore Datawell CDIP buoy 157
Resolution of bathymetry 100x100m
O'Reilly, W. C., & Guza, R. T. (1993). A comparison of two spectral wave models in the southern california bight. Coastal Engineering, 19(19),

9. CDIP Model
Model uses offshore buoy data to determine incoming offshore wave spectra. It then propagates the waves into the depths greater than 10m.

10. MOP Location Site MO634 Carmel River Beach
15m MOP station normally run Location: N W ( )
Water depth: m  (49 ft, 8 fm)
Modeled parameters: wave energy, wave direction

11. Results

12. Buoy Data Spectra Time 1 Time 2 Time 3 Tp=15.39 Dp=292.46 Swh=2.067
Buoy data was sectioned into 3 time periods. Time 1: 1937, Time 2: 2007, Time 3: 2037
Time 1
Time 2
Time 3
Tp=15.39
Dp=292.46
Swh=2.067
Tp=15.38
Dp=291.01
Swh=2.34
Tp=14.29
Dp=288.17
Swh=2.89

13. Buoy Spectra vs. Model Spectra
Time 1
Time 2
model over exaggerates the two peak directions.
Time 3
Tp=14.29
Dp=292
Swh=2.06

14. Buoy Spectra Gridded to Fit Model Spectra
Time 1
Time 3
. In order to compare the buoy and model wave spectra, the data needed to be equally gridded. Since the model data had less points than the buoy data, the buoy data was gridded down to have the same number of point as the model.
Time 2

15. Differencing % Difference between data spectra and model spectra
Time 1
Time 3
The directional spectra were then able to be differenced. This found the percentage of model deviation from the buoy data based on frequency and directional energy. approximately 10-15% differences in all directions. There are a few outliers with higher percentage differences but these could merely be accounted for by a small directional difference. This exaggeration of the two wave directions is also clear in the differencing where the two areas which the models predicts are outlined by 15% differences. The lower frequencies between 0.1 and 0.2 Hz seem to depict a better accuracy of the model to the buoy data.
Time 2

16. Wave Direction vs. Energy
Time 1
Time 3
In all three, the model has less energy further away from the peak direction than the buoy data. However, for both the model and buoy, they all show the two peak directions with one more dominant than the other. In time 2 and 3 the buoy data indicates a smaller peak at 50 degrees where the model does not show this at all. Also, at time 1 and 2, the buoy data shows a few more peaks near the peak direction, which the model does not capture.
Time 2

17. Frequency vs. Energy 95% Confidence Interval using Time 1 Time 3
For the buoy data cross-spectra, the 95% confidence interval was calculated using the chi-squared method. In the frequency and energy plots the model overall proves the model is accurate. The plots indicate accurate peak frequencies with slightly less energy than the buoy data. The buoy data also shows more of fluctuation than the model but this may have been a result of using a larger number of points per segments. However, the entire model is within the 95% confidence interval of the buoy data.
Time 2

18. MUD

20. Sediment Down Canyon

21. Discussion Wave Model describes the data well within ~10-15% error
Model energy falls within 95% confidence intervals
Need longer periods of data over several weeks to compare sufficiently
Use a moored buoy closer to shore

22. References
Datawell BV. (2007). Datawell waverider reference manual. The Netherlands.
De Vries, J. J., Waldron, J., & Cunningham, V. (2003). Field tests of the new datawell DWR-G GPS wave buoy. Sea Technology.
O'Reilly, W. C., & Guza, R. T. (1993). A comparison of two spectral wave models in the southern california bight. Coastal Engineering, 19(19),
O'Reilly, W. C., Herbers, T. H. C., Symour, R. J., & Guza, R. T. (1996). A comparison of directional buoy and fixed platform measurements of pacific swell. Journal of Atmospheric and Oceanic Technology, 13(1),

23. Questions?