In physical oceanography, significant wave height, also known as SWH, or H_s, is the average wave height (trough to crest) of the one-third largest waves. A well developed significant wave is approximately equal to H_m0, defined as four times the standard deviation of the instantaneous displacement from the mean sea level. The American Meteorological Society defines SWH as H_m0.

The original definition resulted from work by the oceanographer Walter Munk during World War II. The significant wave height was intended to mathematically express the height estimated by a "trained observer". It is commonly used as a measure of the height of ocean waves.

A related notation, H_n, where n is a percentage or a fraction, describes the wave height of the n^th percent highest waves. H_n is used to estimate the average maximum wave size (H_0.99) and for certain other analysis. To eliminate any confusion with this H_n notation, the notation H_1/3 is used by the IMO, the U.S. Code of Federal Regulations, most classification societies, as well as many scientific papers. H_s is a special case of H_n.

Other statistical measures of the wave height are also widely used. The RMS wave height, which is defined as square root of the average of the squares of all wave heights, is approximately equal to H_s divided by 1.4.

For example, according to the Irish Marine Institute:

"… at midnight on 9/12/2007 a record significant wave height was recorded of 17.2m at with a period of 14 seconds."

See also

• Sea state
• Rogue wave: A wave of over twice the significant wave height

References and notes

External links

Finnish Institute of Marine Research: Significant wave height