Fourier analysis - A characteristic of remotely sensed images is a parameter called spatial frequency, defined as the number of changes in brightness value per unit distance for any particular part of an image. There are low-frequency and high-frequency areas. Spatial frequency may be enhanced or subdued using Fourier Analysis (an alternative technique is spatial convolution filtering). Fourier analysis mathematically separates an image into its spatial frequency components. It is then possible interactively to emphasize certain groups (or bands) of frequencies relative to others and recombine the spatial frequencies to produce an enhanced image.
The signal received by a pulsed radar is a time sequence of pulses for which the amplitude and phase are measured. The frequency content of this time-domain signal is obtained by taking its Fourier transformation.