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Analysis of Wave Data
After wave data is collected the analysis of that data is typically approached through either:
Statistical analysis provides basic information on the wave climate such as maximum wave height of the record, average wave heigth and root mean-square wave height.
A generally accepted method applied to extract representative statistics from raw wave data is the zero crossing method. According to this method, waves are defined as the portion of a record between two successive zero up crossings. For each recorded burst of wave data the waves are ranked by height (with their corresponding periods), and the following statistics computed:
H10 Average height of the waves, which comprise the top 10% of record.
Maximum Wave Height (Hmax) - Maximum wave height for a given interval of time (typically 17 or 20 minutes).
Mean wave height (Hmean)
Mean Period or Zero crossing period (Tz)
Root Mean Square Wave Height (Hrms)
Significant Wave Height (Hsig) - Average of the heightest one third of the waves measured over a given interval of time. It has been shown that significant wave height corresponds to a visual estimate of waves in that the observer tends to place more emphasis on larger waves. This statistical measurement gained usage based on the impression that in many applications the larger waves are more "significant" than than smaller waves and thus the significant wave height is more representative than the average wave height.
Significant Wave Period (Tsig) - Average period of the highest one-third of the waves determined from large, well defined groups of waves.
Wave analysis by the zero crossing method has limitations, one of which is that the wave period is poorly defined. For example, analysis of a swell with a dominant period of 10 seconds will show a reduction in Tz if locally generated sea is superimposed. Sructure and beach reponse may be strongly dependent on wave period. In these cases an analysis which accounts for all components of wave period, such as spectral anallysis, should be used.
Spectral Analysis, also referred to harmonic analysis, provides a tool capable of generating information on the complicated mixture of waves produced by different storms. Spectral analysis is based on the mathematics of Fourier. Spectral analysis better describes the complete distributions of wave energies and periods than does statistical analysis. Spectral analysis works backward from the complexity of a wave climate to determine the simple components that combine to produce complex wave signals.
Another simplified way to describe spectral analysis is that it provides a method to examine the energy level of a range of wave periods. Spectral analysis makes it possible to determine the period of the waves with the most energy. This statistic (TP1?), yields a more representative wave period for ocean waves than what the zero crossing method can provide.
Directional Wave Spectrum provides the most complete description of a wave climate. This type of analysis provides direction of wave approach as well as the wave energy at a specific period or frequency. The approach angle of waves is instrumental in the generation of currents? and transport?.
The Following Links Provide a Detailed Descriptions of Spectral Analysis