How do I use fft2 to compute the spatial frequency and temporal frequency for a 1D travelling wave?

I have 2 dimensional data for a travelling wave u(x,t) known over the rectangular domain [x,t]= [x1, x2] and [0, t2].

I want to compute the spatial and temporal frequnecy of the wave. Every wave (linear) can be represented as a sum of waves of the form exp(1i (kappa_i x - omega_j t) ). Here kappa_i is the ith spatial frequency present in u(x,t) and omega_j is the jth temporal frequency present in u. How do I obtain these using fft2?