was done by saving the minimum instantaneous water level from the raw 
pressure signal and comparing it to the depth of the shallowest gauge in the 
array being analyzed. If it appeared that the shallowest gauge was at or out of 
the water surface in the trough of any wave passing the pressure gauge, the 
analysis was aborted. This may have been a liberal treatment because it nomi- 
nally allowed the Marsh-McBirney current meters to function within several 
ball diameters of the free surface for a few seconds in some runs, which is 
generally considered unacceptable. The time series of velocity and pressure 
from some of the marginal runs were visually inspected and it was not always 
obvious that the signal was degraded. A more conservative constraint may be 
appropriate if further analysis is pursued. 
Data checking 
A check on data quality was performed by overlaying the frequency spectra 
plots from all gauges for each run that survived the exposure test. Figure E30 
is an example of this. Some features which may not be obvious include: 
a. The main graph shows the frequency spectra (in log coordinates) from 
all gauges plotted out to the Nyquist frequency (1 Hz for the 2-Hz 
subsample frequency) so that background noise floors can be seen. 
b. The pressure spectrum is offset downward by three orders of 
magnitude to isolate its shape from spectral curves from the other 
gauges. Spectra from longshore currents are offset downward by one 
order of magnitude to isolate that group of spectra. Spectra from cross- 
shore currents are plotted with no offset. 
c. Raw spectra are shown throughout except in the low-frequency (includ- 
ing wind-wave) pass band of 0.006 to 0.338 Hz. In the low-frequency 
band, the spectra have been surface normalized as described above 
under “Modifications current meter data.” This helps to determine how 
much surface correction is done even for these shallow gauges, and 
indicates if noise is amplified or reduced in surface normalization. 
d. Modified current meter gains have been applied to the current meter 
spectra in these plots to see if modified spectra form tight groupings for 
each type of gauge. 
e. Curves near the part of the main graph ordinate labeled 'Z' are the 
Z(G) function described above (actually Z(/) is used) after its mean 
value is forced to unity. These functions are plotted on a linear scale. 
These curves are informative in that if they are reasonably flat, the 
surface normalization and gain modification might be considered satis- 
factory. The example shown is reasonably clean. Visual inspection of 
the plot shows some degradation of these curves in time. In some high- 
energy conditions, there is considerable chatter at the lower 
E40 Appendix E Stationary Instrument Data 
