498 CHAPTER 8. LABORATORY MEASUREMENT AND ANALYSIS
respectively, in the defined wave. A more accurate approximation for crest
and trough elevation can be obtained by fitting a spline to the data points
in the region of the crest and trough (Mansard and Funke 1988) . The time
between zero-crossings is the wave period associated with the wave; and
this period can be estimated as the difference between the times associated
with the elevations closest to the zero-crossing locations. A more precise
estimate of wave period can be obtained by fitting a curve to the data
points that span the zero-crossings, and then determining the time of zerocrossing.
A common problem with zero-crossing analysis occurs when the wave
record contains high-frequency fluctuations that can be defined as individual waves during computer analysis unless some preventative action is
taken. The usual solution is to filter out the high-frequency signal, leaving
only those variations that represent gravity wave motion, and to establish a
threshold elevation level that must be exceeded before another zero-crossing
is counted. The filtering parameters and threshold criterion are subjective,
and they may require adjustment to give results that compare well with
hand-analyzed wave records.
After individual waves have been delineated by the zero-upcrossing or
zero-downcrossing method, the wave heights and corresponding wave periods can be used to calculated various statistics and probability distributions. Commonly reported wave statistics determined from “A” waves
include the following:
Mean Wave Height
Root-Mean Squared Wave Height
Mean Wave Period
(8-8)
Other popular statistical wave parameters include:
respectively, in the defined wave. A more accurate approximation for crest
and trough elevation can be obtained by fitting a spline to the data points
in the region of the crest and trough (Mansard and Funke 1988) . The time
between zero-crossings is the wave period associated with the wave; and
this period can be estimated as the difference between the times associated
with the elevations closest to the zero-crossing locations. A more precise
estimate of wave period can be obtained by fitting a curve to the data
points that span the zero-crossings, and then determining the time of zerocrossing.
A common problem with zero-crossing analysis occurs when the wave
record contains high-frequency fluctuations that can be defined as individual waves during computer analysis unless some preventative action is
taken. The usual solution is to filter out the high-frequency signal, leaving
only those variations that represent gravity wave motion, and to establish a
threshold elevation level that must be exceeded before another zero-crossing
is counted. The filtering parameters and threshold criterion are subjective,
and they may require adjustment to give results that compare well with
hand-analyzed wave records.
After individual waves have been delineated by the zero-upcrossing or
zero-downcrossing method, the wave heights and corresponding wave periods can be used to calculated various statistics and probability distributions. Commonly reported wave statistics determined from “A” waves
include the following:
Mean Wave Height
Root-Mean Squared Wave Height
Mean Wave Period
(8-8)
Other popular statistical wave parameters include: