in which x is the variable being studied and m0³ is the area under the spectral curve. This distribution can be used for more or less narrow spectra. This is true for normal wave spectra; they are not too wide. Generally, its frequencies vary between ! = 0:2 and ! = 1:5-2:0.
With this distribution, the probability that the wave amplitude, ³a, exceeds a chosen threshold value, a, can be calculated using: