January 2014 - TD 302 Operating Manual for Pressure 4117/4117R Tide 5217/5217R, Wave & Tide 5218/5218RPage 71
Wave Steepness:
Wave Steepness is generally defined as:
H
ξ
λ
=
where H is wave height. Replacing wavelength with wave period using the equation given by the linear wave theory
the wave steepness becomes:
2
2
H
gT
π
ξ
=
The WTS uses
0
m
H
and
01
m
T
for wave height and wave period.
According to Stokes theory, waves cannot attain heights of more than 1/7 of the wavelength without breaking.
Note! Additional information about the four parameters
Mean Zero Crossing Period, Peak Wave Period, Mean Wave
Period and Energy Wave Period
: If the pressure variations caused by the waves are smaller than what can be
measured by the pressure sensor, the estimated wave periods will approach 1/f
Cut-Off
. This will happen e.g. if the
instrument is deployed too deep to monitor the current sea state.
Spectrum and pressure series
The spectrum is presented as the value of each frequency component in the wave spectrum. Spectre
components outside of the calculated
cut-off
frequencies are set to 0. The first frequency component in the
spectrum is 0 Hz.
Table A 1 Access protection levels
Number of Samples
Number of freq.
components
Resolution at 2 Hz
sampling
Resolution at 4 Hz sampling
256
128
0.0078125 Hz
0.015625 Hz
512
256
0.00390625 Hz
0.0078125 Hz
1024/2048
512
0.001953125 Hz
0.00390625 Hz
