Institute of Ocean Technology and Marine Affairs, National Cheng Kung University, Tainan 70101, Taiwan.
Sensors (Basel). 2013 Aug 19;13(8):10908-30. doi: 10.3390/s130810908.
Accelerometers, which can be installed inside a floating platform on the sea, are among the most commonly used sensors for operational ocean wave measurements. To examine the non-stationary features of ocean waves, this study was conducted to derive a wavelet spectrum of ocean waves and to synthesize sea surface elevations from vertical acceleration signals of a wave buoy through the continuous wavelet transform theory. The short-time wave features can be revealed by simultaneously examining the wavelet spectrum and the synthetic sea surface elevations. The in situ wave signals were applied to verify the practicality of the wavelet-based algorithm. We confirm that the spectral leakage and the noise at very-low-frequency bins influenced the accuracies of the estimated wavelet spectrum and the synthetic sea surface elevations. The appropriate thresholds of these two factors were explored. To study the short-time wave features from the wave records, the acceleration signals recorded from an accelerometer inside a discus wave buoy are analysed. The results from the wavelet spectrum show the evidence of short-time nonlinear wave events. Our study also reveals that more surface profiles with higher vertical asymmetry can be found from short-time nonlinear wave with stronger harmonic spectral peak. Finally, we conclude that the algorithms of continuous wavelet transform are practical for revealing the short-time wave features of the buoy acceleration signals.
加速度计可以安装在海上的浮动平台内部，是用于海洋波观测的最常用传感器之一。为了研究海洋波的非平稳特征，本研究通过连续小波变换理论，推导出海洋波的小波谱，并从波浮标垂直加速度信号合成海面高程。通过同时检查小波谱和合成海面高程，可以揭示短时间波特征。现场波信号被应用于验证基于小波算法的实用性。我们确认谱泄漏和极低频-bin 的噪声会影响估计的小波谱和合成海面高程的精度。探讨了这两个因素的适当阈值。为了从波记录中研究短时间波特征，对圆盘波浮标内加速度计记录的加速度信号进行了分析。小波谱的结果显示出短时间非线性波事件的证据。我们的研究还表明，从更强的谐波谱峰的短时间非线性波中，可以发现更多具有较高垂直非对称性的表面轮廓。最后，我们得出结论，连续小波变换算法对于揭示浮标加速度信号的短时间波特征是实用的。
