wavefromsurfaceelevpsd

[Hm0, fp, Tp, Tm01, Tm02, f, Syy, m0] = wavefromsurfaceelevpsd(Eta, fs, fcL, fcH, nfft, SegmentSize, OverlapSize, dispout)

Description

Calculate wave properties from water surface elevation power spectral density

Inputs

Eta

Water surface elevation time series data in (m)

fs

Sampling frequency that data collected at in (Hz)

fcL=0;

Low cut-off frequency, between 0*fs to 0.5*fs (Hz)

fcH=fs/2;

High cut-off frequency, between 0*fs to 0.5*fs (Hz)

nfft=length(Eta);

Total number of points between 0 and fs that spectrum reports at is (nfft+1)

SegmentSize=256;

Segment size, data are divided into the segments each has a total element equal to SegmentSize

OverlapSize=128;

Number of data points that are overlaped with data in previous segments

dispout=’no’;

Define to display outputs or not (‘yes’: display, ‘no’: not display)

Outputs

Hm0

Zero-Moment Wave Height (m)

fp

Peak wave frequency (Hz)

Tp

Peak wave period (second)

Tm01

Wave Period from m01 (second), Mean Wave Period

Tm02

Wave Period from m02 (second), Mean Zero Crossing Period

f

Frequency (Hz)

Syy

Power spectral density (m^2/Hz)

m0

Zero-Moment of the power spectral density (m^2)

Examples

fs=2; %Sampling frequency
duration=1024; %Duration of the data
N=fs*duration; %Total number of points
df=fs/N; %Frequency difference
dt=1/fs; %Time difference, dt=1/fs
t(:,1)=linspace(0,duration-dt,N); %Time
Eta(:,1)=detrend(0.5.*cos(2*pi*0.2*t)+(-0.1+(0.1-(-0.1))).*rand(N,1));
[Hm0,fp,Tp,Tm01,Tm02,f,Syy,m0]=wavefromsurfaceelevpsd(Eta,fs,0,fs/2,N,256,128,'yes');

References

Welch, P. (1967). The use of fast Fourier transform for the estimation of power spectra: a method based on time averaging over short, modified periodograms. IEEE Transactions on audio and electroacoustics, 15(2), 70-73.