CREST/TROUGH/MWL CONTOUR MAPS

     The large waves in a confused seas are difficult to describe.  Just what is a wave height or
wave trough in chaotic storm condition?  After considerable study, the following "quartile-wave"
definitions are being proposed.  All of the water surface elevations above and below mean water
level from the grid of the SRA measurements over a specified region are ranked in order of
increasing size. The 50 percentile elevation corresponds very nearly to the  mean water level. A
wave crest is defined as a "bump" of water that exceeds the 75 percentile elevation.   Similarly, a
wave trough is taken as a water surface depression which drops below the 25 percentile
elevation.  The small sea surface irregularities which do not get outside of the [25 75]-percentile
range are taken as being not significant.

     A special type of contour map was designed to make the grouping patterns of the quartile
waves clearly evident to the eye.  The procedure is based on a further use of the ranked elevations
is developed as follows.  The ranked elevations are used to establish the [1, 3, 5, 10, 15, 20, 25,
75, 80, 85, 90, 95, 97, 99]-percentile elevations.  The grid of SRA elevations is then contoured at
these 20 levels.  A colorbar coding is introduced which fills the contours outward from zero.   All
elevations between the 25- and the 75-percentile elevations were left white.  Finally, a black
contour iss placed at mean water level.  The crests are colored orange to red, while the troughs
are colored with shades of blue.

     The code for the analysis was developed with Matlab scientific software.  Since the
Matlab contour package fills contours always upward from lower value to higher value, it was
necessary to develop special routines using the "patch" command in Matlab to force the creation
of the "outward" contour maps.  A special colormap was also modified from the "jet" Matlab
color map which started the red shading at the 75th percentile introduced the blue shades below
the 25th percentile.