Theoretical responses of three-dimensional spatial filters. A data example is presented which demonstrates the practical use of extended array filters, both implemented in the field and in the computer. In areas with strong coherent noise, a field-implemented extended source array gives a signal-to-coherent noise improvement which cannot be obtained in data processing. In other areas, computer implementation of the extended arrays gives signal-to-coherent noise improvement as effectively as a field-implemented extended source array. Noise reduction is done more effectively by extended array filtering than by vertical and horizontal stacking prior to CDP stacking.--Modified journal abstract.