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 , yl ) - φmeas ( xl , yl )
c-m
E j- phase
(10)
j
L l =1
where
φcjomputed ( xl , yl ) = the computed model elevation phase for constituent j at
measurement location (xl, yl)
φmeas ( xl , yl ) = the measured elevation phase for constituent j at
j
measurement location (xl, yl)
Note that E c--pmase excludes stations with phase differences larger than 50 deg
j h
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
m
j
Eastcoast databases and E mamp for the measured data) whereas the bottom
j-
compares phase errors ( E c--pmase for each of the Eastcoast databases and E mphase for
j-
j h
the measured data). In each chart, the x-axis corresponds to the tidal constituent