In
physical oceanography, the
significant wave height (
SWH or
Hs) is defined traditionally as the mean
wave height (
trough to
crest) of the highest third of the
waves (
H1/3). Nowadays it is usually defined as four times the
standard deviation of the surface elevation – or equivalently as four times the square root of the zeroth-order moment (
area) of the
wave spectrum. The symbol
Hm0 is usually used for that latter definition. The significant wave height may thus refer to
Hm0 or
H1/3; the difference in magnitude between the two definitions is only a few percent.