Topography 5 min gridded resolution (ETOPO5)1 bathymetric database which
defines bathymetry on a coarse resolution 5' x 5' grid and extends over all the
world oceans.
An updated WNAT tidal database, Eastcoast 1995, was developed in 1995.
The Eastcoast 1995 grid, shown in Figure 3, consists of 31,435 nodes and
58,369 elements, and was considered a large finely variable graded grid at the
time it was generated. This grid was also generated under the guidance of the
wavelength to grid-size ratio criterion. Element sizes vary from 5 to 15 km at the
coastline, to about 100 km in the deep ocean as shown in Figure 4. The
bathymetry for this tidal constituent database, shown in Figure 5, was signifi-
cantly improved by using both the ETOPO5 database and the NOS sounding
bathymetric database (National Ocean Service (NOS) 1997).2 The NOS
bathymetric database represents the raw sounding tracks from surveys and
typically extends only to the continental shelf break in U.S. coastal waters.
ADvanced CIRCulation (ADCIRC) was the hydrodynamic numerical model
used to compute the Eastcoast 1991 and Eastcoast 1995 tidal databases. The
Eastcoast 1991 in its time provided invaluable results, until Eastcoast 1995
database superceded it with improved values. Eastcoast 1991 had average tidal
constituent errors in amplitude between 18.2 and 45.3 percent, and average errors
in phase between 8.3 and 27.5 deg for predictive WNAT tidal computations
driven by the K1, O1, Q1, M2, S2, N2, and K2 constituents. Eastcoast 1995 had
average errors in amplitude between 9.4 and 29.0 deg, and average errors in
phase between 7.1 and 15.0 deg for similar computations. Further improvements
in local and global accuracy of tidal constituents were desired for the WNAT
domain.
In this report, the development of the latest and most accurate tidal database
for the WNAT domain is described. The most significant improvements include
a more refined and strategically laid out unstructured grid of the WNAT domain
as well as significant improvements in the definition of bathymetry in select
regions. Specifically, a 254,629-node unstructured finite element grid was
developed using the combined wavelength to grid size and TLS criteria with a
defined minimum resolution equal to 1 to 2 km in most areas and a maximum
resolution equal to 25 km. Furthermore, improved resolution allowed for better
precision in the placement of coastal boundaries as well as the addition of
important islands. An updated WNAT bathymetry created from the ETOPO5,
NOS and DNC (U.S. Department of Defense 1999) databases was also imple-
mented. The open boundary was forced with the most current Le Provost et al.
(1998) tidal database, FES95.2, which incorporates assimilated satellite altimetry
based sea surface data. Finally, data from elevation recording stations scattered
throughout the WNAT domain were updated and were used for more extensive
model validation.
1
Data obtained from National Geophysical Data Center, National Oceanic and Atmospheric
Administration, Boulder, CO, 80303-3328, 1988, World Wide Web page accessed on 2 May 2001,
http://edcwww.cr.usgs.gov/glis/hyper/guide/etopo5.
2
Additional information available on the World Wide Web at
http://www.ngdc.noaa.gov/mgg/fliers/97mgg02.html).
3
Chapter 1 Introduction and Objectives
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