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Costal Inlets Research Program
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Measurement Procedures and Data Analysis
Figure 14. Time series of water-surface elevation η at wave generator (Gauge 21 and Guage 15)
TR-02-27
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Figure
13.
Comparison
of
targeted
and
measured
spectra
for
wave
generation
Data
Analysis
The
velocity
data
were
analyzed
to
determine
wave
direction
with
a
program
adapted
from
a
PUV
(pressure
and
horizontal
velocity
components)
directional
wave
gauge
analysis
program
as
outlined
by
Earle,
McGehee,
and
Tubman
(1995).
Because
water
level
variation
was
unavailable
at the
location
of the
current
meter
probe,
the
wave
direction
and
energy
for
each
frequency
were
determined
from
the
harmonics
of the
directional
spectum
related
to
velocity.
These
harmonics
are
calculated
from
auto-
and
cross-spectra
determined
from
a
Fast
Fourier
Transform
(FFT)
of the
velocity
records.
Wave
data
were
analyzed
in
two
ways. A down-crossing analysis
was
performed
on the
time
series
of
water
elevations
as
well
as spectral analysis
using
an
FFT.
The
down-crossing analysis produced the calculated
parameters
shown
in
Table
3.
FFT
or
single-channel
frequency
domain
analysis
was
performed
over
the
entire
20,400
data
points
(∆
t
=
0.05
sec).
In the analysis, the
mean
was
removed
and a
cosine
square
taper
applied
over
10 percent of the
data
at the
beginning
and
end
of the
data
record.
The
spectral
parameters
calculated
are
listed
in
Table
4.
19
Chapter
3
Measurement
Procedures
and
Data
Analysis
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