Great Lakes Wave Measurement Definitions

[Rorke]

Here are some helpful definitions.

WVHT - Significant Wave Height is the average height (meters) of the highest one-third of the waves during a 20 minute sampling period.

SwH - Swell height is the vertical distance (meters) between any swell crest and the succeeding swell wave trough.

SwP - Swell Period is the time (usually measured in seconds) that it takes successive swell wave crests or troughs pass a fixed point.

WWH - Wind Wave Height is the vertical distance (meters) between any wind wave crest and the succeeding wind wave trough (independent of swell waves).

WWP - Wind Wave Period is the time (in seconds) that it takes successive wind wave crests or troughs to pass a fixed point.

SwD - The direction from which the swell waves at the swell wave period (SWPD) are coming. The units are degrees from true North, increasing clockwise, with North as 0 (zero) degrees and East as 90 degrees.

WWD - The direction from which the wind waves at the wind wave period (WWPD) are coming. The units are degrees from true North, increasing clockwise, with North as 0 (zero) degrees and East as 90 degrees.

STEEPNESS - Wave steepness is the ratio of wave height to wave length and is an indicator of wave stability. When wave steepness exceeds a 1/7 ratio; the wave becomes unstable and begins to break.

APD - Average Wave Period is the average period (seconds) of the highest one-third of the wave observed during a 20 minute sampling period.

MWD - The direction from which the waves at the dominant period (DPD) are coming. The units are degrees from true North, increasing clockwise, with North as 0 (zero) degrees and East as 90 degrees. See the Wave Measurements section.