In this work we consider the evolution of power spectra of waves during a period of one year. Soukissian and Samalekos (2005) have proposed a segmentation method for significant wave height based on determining periods of stability, increase and decrease using time-series techniques. The second segmentation method is based on the mean value over a moving window, and uses a fixed-width band to determine the change-points in the register. We compare both segmentation methods for several spectral characteristics and give a statistical analysis of duration and intensity of sea states in each case.

INTRODUCTION

In this work we consider the evolution of power spectra of waves during a period of one year with data from one recording station situated at Waimea Bay, Hawaii. Using the wave-height record we calculate the spectra every 15 minutes in order to capture the short term evolution of some wave characteristics that can be obtained from the spectra. WAFO was used for obtaining the spectra and the spectral characteristics. Soukisissian and Samalekos (2005) have proposed a segmentation method for significant wave height based on determining periods of stability, increase and decrease using time-series techniques. Their method is based on local linear regression and the initial and end points of the intervals are extreme points (local maxima and minima) of the time series. They use a cost function to determine the best configuration of intervals. We apply this method to some spectral characteristics and compare the results obtained with another segmentation method which will be described next. The second segmentation method is based on calculating mean values over moving windows, and using a fixed-width band to determine change points in the wave-height data. Those intervals in which the values remain within a fixed-width interval around the mean are considered to be stationary, those in which the values go above (or below) will be considered increasing (or decreasing).

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