Table 12 



Sea State Parameters 



Symbol | Description | Units 



Basic Terms 



a 



Amplitude 



m 



c 



Phase velocity or celerity 



m/s 



°c 



Group velocity 



m/s 



f 



Frequency 



Hz 



H 



Wave height 



m 



L 



Wave length measured in the direction of wave propagation 



m 



T 



Wave period 1 1f 



s 



e 



Direction of wave propagation as used in directional spectra 



deg 



df 



Basic frequency increment in discrete Fourier analysis 



Hz 



o 



Standard deviation 



m ; 



General Parameters 



f o 



Spectral peak frequency MT p 



Hz 



H s 



Significant wave height defined as the highest one-third of the wave 

 heights calculated as H 1/3 downcrossinl) ; or H U3 upcmssinq 



m 



T o 



Spectral peak period 1 lf p 



s 



Time Domain Analysis Functions 



H 1/3,d 



Zero-downcrossing significant wave height. Average of the highest 

 one-third zero-downcrossing wave heights 



m 



H U3.u 



Zero-upcrossing significant wave height 



m 



Frequency Domain Analysis Parameters 



f P 



Spectral peak frequency. This frequency may be estimated by different 

 methods, such as: (1) Frequency at which S n (f) is a maximum; 

 (2) Fitting a theoretical spectral model to the spectral estimates 



Hz 



H mO 



Estimate of significant wave height, Wm 



m 2 /Hz 



m n 



nth moment of spectral density 



m 2 /s n 



Sff) 



Spectral density 



m 2 /Hz 



T o 



Spectral peak period Mf B 



s 



Directional Parameters and Functions 



k 



Wave vector 



rad/m 



d(f,Q) 



Directional spreading function 



deg 



sif,ei 



Directional spectral density 



(m 2 /Hz)/ 

 deg 



a 



Wave direction. This is the commonly used wave-direction parameter, 

 representing the angle between true north and the direction from which 

 the waves are coming. Clockwise is positive in this definition 



deg 



e 



Direction of wave propagation describing the direction of k. Counter- 

 clockwise is positive 



deg 



e m w 



Mean wave direction as a function of frequency. The mean of all Q m lfl 

 is known as the overall wave direction. 



deg 



(Adapted from IAHR Working Group on Wave Generation and Analysis 

 (1989)) 



Chapter 5 Analysis and Interpretation of Coastal Data 



87 



