PcorFFTFun

[Eta,ftailcorrection]=PcorFFTFun(input,fs,duration,nfft,h,heightfrombed,fminpcorr,fmaxpcorr,ftailcorrection,pressureattenuation,autofmaxpcorr,dispout)

DESCRIPTION

Apply pressure correction factor to water depth data from pressure gauge reading using FFT

INPUT

input=importdata(‘h.mat’);

Load water depth (h)/surface elevation (Eta) data and rename it “input” in (m)

fs=10;

Sampling frequency that data collected at in (Hz)

duration=1024;

Duration time that data collected in input in each burst in second

nfft=2^10;

NFFT for Fast Fourier Transform

h=1;

Mean water depth in (m)

heightfrombed=0.0;

Sensor height from bed

fminpcorr=0.15;

Minimum frequency that automated calculated fmaxpcorr can have if autofmaxpcorr=’on’ in (Hz)

fmaxpcorr=0.8;

Maximum frequency for applying pressure attenuation factor

ftailcorrection=1;

Frequency that diagnostic tail apply after that (typically set at 2.5fm, fm=1/Tm01)

pressureattenuation=’all’;

Define if to apply pressure attenuation factor or not

pressureattenuation=’off’: No pressure attenuation applied

pressureattenuation=’on’: Pressure attenuation applied without correction after fmaxpcorr

pressureattenuation=’all’: Pressure attenuation applied with constant correction after fmaxpcorr

autofmaxpcorr=’on’;

Define if to calculate fmaxpcorr and ftailcorrection based on water depth or not

autofmaxpcorr=’off’: Off

autofmaxpcorr=’on’: On

dispout=’on’;

Define to display outputs or not (‘off’: not display, ‘on’: display)

OUTPUT

Eta

Corrected Water Surface Level Time Series (m)

EXAMPLE

[Eta]=PcorFFTFun(input,10,1024,2^10,1.07,0.05,0.04,0.8,'all','off','on');

NOTES

This function can be used as a standalone command in Matlab/GNU Octave command line or it can be embedded in Matalb/GNU Octave script file (.m file) as:

[Eta,ftailcorrection]=PcorFFTFun(input,fs,duration,nfft,h,heightfrombed,fminpcorr,fmaxpcorr,ftailcorrection,pressureattenuation,autofmaxpcorr,dispout);

Example for using a provided sample input file:

[Eta]=PcorFFTFun(input,10,1024,2^10,1.07,0.05,0.04,0.8,'all','off','on');

In case of using a pressure attenuation correction function, choosing a proper upper limit for applying a correction is essential. If the upper limit is chosen unreasonably high, it will lead to a wrong over-estimation of the results. The under-estimation also can happen, if the upper limit is chosen unreasonably low. The waves that are large enough that can be sensed by a sensor should be included in attenuation correction. Note that pressure from small waves with high frequency can be damped in the water column and therefore may not reach a sensor depth. In that case, these small waves should not be included in attenuation correction. Wave height, wave frequency, water depth, height of a sensor above a seabed all play roles on if a wave effect reaches down to a sensor depth or not. Because of that, a deployment situation and wave properties should be used to define the highest frequency that a sensor senses its effect. Pressure correction should not be applied beyond that point. (refer to Applying Pressure Response Factor section)