So, alternatively eta (t) can be represented as real part of that summation, which is shown there with a n representing or equal to twice a into the Fourier coefficient, a n in which a suffix 0 equal to 0 for eta to be mean 0 process. So, then with this background a random sea wave may be represented as a infinitely small infinitely sum of a sinusoidal components travelling with different wave numbers and frequencies and directions which can be represented given as the equation represented there and this is referred to as single summation model.