where a j and b j are independent random variables from a Gaussian distribution with variance of S ( ω) d ω and d ω is the frequency separa- tion of the harmonics. It can be proved that the random variable c j is Rayleigh distributed with a root mean square value of 2 S( ω j ) dω and ϕ j is uniformly distributed in [0, 2 π]. According to this notation, A j is a wave complex amplitude given by: