The Fourier domain DMO methods give appropriate results for 2-D lines but are time-consuming. In 3-D surveys, their implementation becomes more difficult because the spatial sampling rate as a function of azimuth is variable and irregular. In contrast to Fourier domain DMO methods, the integral DMO method is not affected by this problem and provides cheap processing because of the limited extent of the operator (which is two-dimensional and dip-limited). However, the implementation of an integral method requires explicit knowledge of the operator as well as of the weight applied to each operation. The next section describes the shape of the operator, and the second section states three rules that the DMO operator must satisfy.