Approximation of the joint probability density of wave steepness and height with a bivariate gamma distribution

A bivariate gamma distribution is fitted to an empirical joint probability density of wave steepness and height for deep water waves. A transformation of this distribution is also fitted to waves from a wave tank experiment in order to observe how the skewness of the bivariate gamma distribution changes. The quality of the obtained fits is compared with fits of a Gumbel copula for the same data.