Example (MATLAB Version)¶
Here is an example shows how to use OCEANLYZ. In this example, we use a provided sample file “waterpressure_5burst.csv” as input data. This sample file contains five bursts of water pressure data recorded with a pressure sensor. Sample file may be downloaded at https://github.com/akarimp/oceanlyz/releases/tag/2.0 .
Measurement properties for “waterpressure_5burst.csv” are:
|Data type||Water pressure||obj.InputType=’pressure’|
|Number of recorded burst (n_burst)||5||obj.n_burst=5|
|Sampling frequency (fs)||10 (Hz)||obj.fs=10|
|Recording duration (burst_duration)||1024 (second)||obj.burst_duration=1024|
|Pressure sensor height from bed (heightfrombed)||0.05 (m)||obj.heightfrombed=0.05|
|Mean water depth (h)||Varies in each burst|
To start using OCEANLYZ, first, we need to be in a folder that contains OCEANLYZ files. Assume OCEANLYZ files are in ‘C:\oceanlyz_matlab’. First, we change current working directory to OCEANLYZ folder as:
cd('C:\oceanlyz_matlab') %Change current working directory to OCEANLYZ folder
Next, we download water pressure dataset (“waterpressure_5burst.csv”), we unzip it and copy sample files in a desired folder.
Assume we are currently in OCEANLYZ folder ‘C:\oceanlyz_matlab’ and downloaded sample data file is stored in ‘C:\oceanlyz_matlab\Sample_Data’. Then, we load data as:
current_folder = pwd; %Current (OCEANLYZ) path cd('C:\oceanlyz_matlab\Sample_Data') %Change current folder to a folder that contains data file water_pressure = importdata('waterpressure_5burst.csv'); %Load data cd(current_folder) %Change current folder back to initial (OCEANLYZ) folder
We can plot data if we need to as:
plot(water_pressure) xlabel('Sample points') ylabel('Water Pressure (N/m^2)')
Then, we need to create an OCEANLYZ object as:
%Create OCEANLYZ object ocn = oceanlyz;
Next, we assign wave data to OCEANLYZ object as:
%Input data ocn.data = water_pressure;
Now, we set up OCEANLYZ properties as:
ocn.InputType='pressure'; ocn.OutputType='wave+waterlevel'; ocn.AnalysisMethod='spectral'; ocn.n_burst=5; ocn.burst_duration=1024; ocn.fs=10; ocn.fmin=0.05; ocn.fmax=ocn.fs/2; ocn.fmaxpcorrCalcMethod='auto'; %Only required if ocn.InputType='pressure' ocn.Kpafterfmaxpcorr='constant'; %Only required if ocn.InputType='pressure' ocn.fminpcorr=0.15; %Only required if ocn.InputType='pressure' ocn.fmaxpcorr=0.55; %Only required if ocn.InputType='pressure' ocn.heightfrombed=0.05; %Only required if ocn.InputType='pressure' ocn.dispout='yes'; ocn.Rho=1024; %Seawater density (Varies)
After all required properties are set, we can run OCEANLYZ as:
Output is stored as a structure array. Name of output is ‘oceanlyz_object.wave’. Field(s) in this structure array can be called by using ‘.’ For example oceanlyz_object.wave.Hm0 contains zero-moment wave height and oceanlyz_object.wave.Tp contains peak wave period.
Here we show how to plot zero-moment wave height:
Hm0 = ocn.wave.Hm0; %zero-moment wave height plot(Hm0) xlabel('Burst Number') ylabel('Hm0 (m)')
Similarly, we can plot wave spectrum for the first burst:
f = ocn.wave.f; %frequency of the first burst Syy = ocn.wave.Syy; %spectrum of the first burst plot(f(1,:),Syy(1,:)) xlabel('f (Hz)') ylabel('Syy (m^2/Hz)')
If data are collected in continuous mode and you need to analyze them in smaller blocks, you can analyze it in a burst mode. For that, you choose n_burst and burst_duration as follow:
The burst_duration is equal to a period of time that you want data analyzed over that. For example, if you need wave properties reported every 15 min, then the burst_duration would be 15*60 second.
the n_burst is equal to the total length of the time series divided by the burst_duration. The n_burst should be an integer. So, if the total length of the time series divided by the burst_duration leads to a decimal number, then data should be shortened to avoid that.
- Welch spectrum is used to calculate a power spectral density. In all spectral calculation, a default window function with a default overlap window between segments are used.
- If fmaxpcorrCalcMethod=’auto’, then OCEANLYZ calculates fmaxpcorr based on water depth and a sensor height from a seabed (refer to Applying Pressure Response Factor section). A maximum value for calculated fmaxpcorr will be limited to the value user set for fmaxpcorr.