Dispersion relations for rotational gravity water flows having two jumps in the vorticity distribution

We derive the dispersion relation for periodic traveling waves propagating at the surface of water with a layer of constant non-zero vorticity situated between two layers of irrotational flow. Due to the complicated nature of the dispersion relation - a fourth order algebraic equation with intricate coefficients - we also give an estimate of a very simple form involving only the levels at which the vorticity has jumps. Our formula generalizes a corresponding one from [5].