ABSTRACT
This report deals with second order, two-dimensional low frequency waves induced by the non-linear interactions of the first order component waves in a two-dimensional short wave field. The convolution to calculate the averaged two-dimensional low frequency wave spectrum is developed. Any given
two-dimensional short wave spectrum can be used as an input of this
convolution. The theoretical results are compared with field data measured in the North Sea. The observed low-frequency wave energy is considerably in excess of the predicted value which may be due to low-frequency waves not correlated with the local wind waves.