Wave can be classified into:
- Regular wave - a periodic wave with a single period.
- Random wave (spectrum) - a superposition of a number of regular linear waves of differing heights and periods.
There are two types of regular wave:
- Linear wave theory (Airy) - symmetric (Crest height = Trough height);
- Non-linear wave theories (Stoke's 5th order theory, Dean's stream function theory etc.) - asymmetric (Crest height > Trough height).
Random wave also known as spectrum. A real sea state is best described by a random wave model, since the ocean waves are irregular and random in shape, height, length and speed of propagation. Examples of random wave are JOHNSWAP, ISSC etc.