Question

what does the height of the crest show

Answer 1

Hlo here is ur answer.
Crest heights is needed in many applications.
Crest height distributions based on the information contained in the spectrum. A first-order description is sufficient for trough to crest wave heights because the second-order correction raises both crest and trough. For good accuracy, it is, however, necessary to account for the variation in the wave envelope between trough and crest. 
This may helps U!!