The computed to measured phase error for each constituent j was calculated

as an absolute average error defined over a region as:

1 L computed

= ∑ φj

( xl , *y*l ) - φmeas ( xl , *y*l )

(10)

where

φcjomputed ( xl , *y*l ) = the computed model elevation phase for constituent *j *at

measurement location (*x*l, yl)

φmeas ( xl , *y*l ) = the measured elevation phase for constituent *j *at

measurement location (*x*l, yl)

Note that E c--pmase excludes stations with phase differences larger than 50 deg

associated with very small corresponding amplitudes and highly unreliable

measurement data.

Table 4 provides the computed to measured amplitude and phase errors for

each of the seven astronomical constituent in each defined portion of the domain.

The constituents in Eastcoast 2001 are predicted with proportional standard

deviation amplitude errors ranging between 6.2 and 14.1 percent and absolute

average phase errors between 8.1 and 12.9 percent. Generally, the amplitude

errors for the larger constituents, K1, O1, M2, S2, and N2 tides, are smaller than the

errors of the Q1 and K2 constituents. In regions dominated by diurnal constitu-

ents, the diurnal amplitude errors are smaller than the semidiurnal errors, and

vice versa for regions dictated by semidiurnal tides. As noted previously, along

the Atlantic coast the M2 tide dominates, whereas the O1 and K1 diurnal constitu-

ents govern in the Gulf of Mexico.

A comparison of Eastcoast 2001 error levels to that of previous databases as

well as the estimated measured field data errors is useful in ascertaining the

improvements derived from the additional grid resolution and enhanced

bathymetry. For the Eastcoast 1991 database, error levels were obtained from a

previous study (Westerink, Luettich, and Scheffner 1993; Westerink, Luettich,

and Muccino 1994). For the Eastcoast 1995 database, the average computed to

measured data constituent errors was calculated in a similar manner as the errors

for Eastcoast 2001 using the updated 101 stations. Errors were calculated as

computed to measured data proportional standard deviation over the entire

domain as well as the defined regions. Amplitude and phase errors for each tidal

database are given in Tables 5-9 globally and by defined regions, and are graphed

in Figures 147-151. Each figure corresponds to a defined region and is com-

posed of two bar charts; the top compares amplitude errors ( E c--amp for each of the

Eastcoast databases and E mamp for the measured data) whereas the bottom

compares phase errors ( E c--pmase for each of the Eastcoast databases and E mphase for

the measured data). In each chart, the x-axis corresponds to the tidal constituent

simulated and the y-axis represents the magnitude of the error.

19

Chapter 5 Model Results

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