In this paper, we discuss expressions of potential fields in the frequency domain and filter operations by the two dimensional Fast Fourier Transform method in interpretations of the gravity and the magnetic anomalies. Especially by using the complex Fourier series, the representations in the frequency domain, which correspond to differentiation, integration and continuation in the spatial domain, are simplified, and the meanings of the coefficients used in the two-dimensional filter operation are clarified. Some useful filter operations are described, which are the pseudo-gravity, reduction to the pole, vector magnetic anomalies derived from the total magnetic field, upward continuation， three dimensional density and magnetization structures confined by horizontal planes and analytic signals. A simple new iterative method for analyzing double-layer structures from gravity (or pseudogravity) data is also proposed, in which an expression in the frequency domain by Parker (1972) is used as a model function. Either of the subsurface structure or the two-dimensional variation of the density (or the magnetization) can be obtained by this method.

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