512 CHAPTER 8. LABORATORY MEASUREMENT AND ANALYSIS
noise signal for all three gauges. This frequency domain method concentrates on the phase differences between gauges, and it provides improved
stability in the estimates and an increased range of frequency resolution
with less sensitivity to gauge spacing. Laboratory tests by Mansard and
Funke showed good agreement between incident wave spectra calculated
by the least-squares method and corresponding spectra measured concurrently in an adjacent channel without a reflective structure. Like the Goda
Method, Mansard and Funke’s method is a linear theory analysis, and it assumes the gauges are placed over a flat bottom. Most laboratories presently
employ either the Goda Method or the Mansard and Funke Method for estimating incident and reflected spectra in wave flumes, and the Mansard
and Funke Method is considered to be a little more accurate.
Field application of Mansard and Funke’s (1980) least-squares method
was described by Nelson and Gonsalves (1990) . They applied the technique to resolve incident and reflected infragravity wave spectra using wave
data obtained in the surf zone from five pressure sensors mounted on poles
0.4 m above the bed. Sampling frequency was 2 Hz and gauge spacing was
selected to resolve frequencies in the infragravity band. Nelson and Gonsalves reported significant reflection for wave periods of 20 s and nearly
complete reflection for wave periods greater than 30 s.
Gaillard, et al. (1980) described a linear analysis technique that utilizes
water surface time series synoptically measured at three spatially separated
wave gauges on a line perpendicular to the wave crests. The method is
similar to that of Mansard and Funke (1980). Autospectra from each gauge
and cross-spectra between gauges are combined to estimate the incident and
reflected spectra. Singularities that arise using a two-gauge method are
avoided, thus extending the resolution over a wider range of frequencies.
Vertical Array
Several investigators have described techniques for resolving incident and
reflected two-dimensional waves using a wave gauge (or pressure gauge) and
current meter located on the same vertical line in the water column.
Guza, et al. (1984) developed a time domain procedure for resolving
long wave incident and reflected wave trains. The method combines synoptic values of horizontal water velocity and sea surface elevation from a
pressure gauge and current meter to form new time series of incident and
reflected long waves.
The pressure gauge time series is first transformed to equivalent sea
surface elevations using linear wave theory. The resulting first-order time
series representation of the sea surface is given by Eqn. 8.29, which can be
written as
noise signal for all three gauges. This frequency domain method concentrates on the phase differences between gauges, and it provides improved
stability in the estimates and an increased range of frequency resolution
with less sensitivity to gauge spacing. Laboratory tests by Mansard and
Funke showed good agreement between incident wave spectra calculated
by the least-squares method and corresponding spectra measured concurrently in an adjacent channel without a reflective structure. Like the Goda
Method, Mansard and Funke’s method is a linear theory analysis, and it assumes the gauges are placed over a flat bottom. Most laboratories presently
employ either the Goda Method or the Mansard and Funke Method for estimating incident and reflected spectra in wave flumes, and the Mansard
and Funke Method is considered to be a little more accurate.
Field application of Mansard and Funke’s (1980) least-squares method
was described by Nelson and Gonsalves (1990) . They applied the technique to resolve incident and reflected infragravity wave spectra using wave
data obtained in the surf zone from five pressure sensors mounted on poles
0.4 m above the bed. Sampling frequency was 2 Hz and gauge spacing was
selected to resolve frequencies in the infragravity band. Nelson and Gonsalves reported significant reflection for wave periods of 20 s and nearly
complete reflection for wave periods greater than 30 s.
Gaillard, et al. (1980) described a linear analysis technique that utilizes
water surface time series synoptically measured at three spatially separated
wave gauges on a line perpendicular to the wave crests. The method is
similar to that of Mansard and Funke (1980). Autospectra from each gauge
and cross-spectra between gauges are combined to estimate the incident and
reflected spectra. Singularities that arise using a two-gauge method are
avoided, thus extending the resolution over a wider range of frequencies.
Vertical Array
Several investigators have described techniques for resolving incident and
reflected two-dimensional waves using a wave gauge (or pressure gauge) and
current meter located on the same vertical line in the water column.
Guza, et al. (1984) developed a time domain procedure for resolving
long wave incident and reflected wave trains. The method combines synoptic values of horizontal water velocity and sea surface elevation from a
pressure gauge and current meter to form new time series of incident and
reflected long waves.
The pressure gauge time series is first transformed to equivalent sea
surface elevations using linear wave theory. The resulting first-order time
series representation of the sea surface is given by Eqn. 8.29, which can be
written as