where θ0 is the main direction and p(ω) is an integer which depends on frequency. This model describes well the local wind generating waves but fails when the wave field contains propagating waves from other directions like swells.In order to account for this problem, we assume that the wave field is is composed by a local wind generated one (located at direction θ0) and a propagating field (located at direction θ1). Thus, the directional spectrum can be expressed by