Use of Collocated Sensors to Measure Coastal Wave Reflection
Publication: Journal of Waterway, Port, Coastal, and Ocean Engineering
Volume 125, Issue 1
Abstract
Two different methods for estimating frequency-dependent reflection coefficients for waves incident on a coastline using collocated measurements of elevation (or pressure) and horizontal current are investigated by simulating time series with known true reflection coefficients and added uncorrelated noise. The methods are applicable to measurements made in the nearshore zone where waves propagate essentially shore-normally. A time domain method is shown to introduce a significant positive bias in the estimated reflection coefficient. A contour plot is calculated giving the bias as a function of the estimated reflection coefficient and the coherence between the estimated incoming and outgoing wave time series, which can be used to provide corrections for the bias. A new principal component analysis (PCA) technique is found to be essentially bias-free. For this method, 95% confidence levels on zero reflection coefficient are computed for a range of numbers of degrees of freedom. Spatial separation between the sensors equivalent to a time delay, at the wave phase velocity, of τx produces a spurious peak with a reflection coefficient of one at frequency 1/(4τx). The peak is very sensitive to small errors in estimating the time delay, which result in apparent reflection coefficients even higher than one. The conclusion is that the time delay must be made as small as possible in order to push the spurious peak to a high frequency. Application of these results is demonstrated using field data taken on a natural beach.
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References
1.
Baquerizo, A., Losada, M. A., Smith, J. K., and Kobayashi, N. (1997). “Cross-shore variation of wave reflection from beaches.”J. Wtrwy., Port, Coast., and Oc. Engrg., ASCE, 123(5), 274–279.
2.
Davidson, M. A., Bird, P. A. D., Bullock, G. N., and Huntley, D. A. ( 1996). “A new non-dimensional number for the analysis of wave reflection from rubble mound breakwaters.” Coast. Engrg., 28, 93–120.
3.
Elgar, S., Herbers, T. H. C., and Guza, R. T. ( 1994). “Reflection of ocean surface gravity waves from a natural beach.” J. Phys. Oceanography, 24(7), 1503–1511.
4.
Frigaard, P., and Brorsen, M. ( 1995). “A time-domain method for separating incident and reflected irregular waves.” Coast. Engrg., 24, 205–215.
5.
Guza, R. T., and Bowen, A. J. ( 1976). “Resonant interactions for waves breaking on a beach.” Proc., 15th Conf. on Coast. Engrg., ASCE, New York, 560–579.
6.
Huntley, D. A., and Davidson, M. A. (1998). “Estimating the directional spectrum of waves near a reflector.”J. Wtrwy., Port, Coast., and Oc. Engrg., ASCE, 124(6), 312–319.
7.
Huntley, D. A., Simmonds, D. J., and Davidson, M. A. ( 1995). “Estimation of frequency-dependent reflection coefficients using current and elevation sensors.” Proc., Coast. Dyn. '95, ASCE, New York, 57–68.
8.
Kajima, R. ( 1969). “Estimation of incident wave spectra under the influence of reflection.” Proc., 13th Congr., Vol. 5.1, International Association for Hydraulic Research, Delft, The Netherlands, 285–288.
9.
Nutall, A. H. ( 1971). “Spectral estimation by means of overlapped FFT processing of windowed data.” Naval Underwater Sys. Ctr. Rep. No. 4169 (and supplement NUSC TR-4169S), New London, Conn.
10.
Tatavarti, R. V. S. N., Huntley, D. A., and Bowen, A. J. ( 1988). “Incoming and outgoing wave interactions on beaches.” Proc., 21st Conf. on Coast. Engrg., ASCE, New York, 136–150.
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Received: Aug 11, 1997
Published online: Jan 1, 1999
Published in print: Jan 1999
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