Careful stacking of seismic data can remove most of the noise from the recorded earth signals. The signals may have been recorded and processed without filtering of the signal frequencies, nevertheless, the signals will have been modified by the natural filtering from transmission through the earth. Therefore, the spectrum of the recorded signal will most likely suffer considerable attenuation of high, and some low, frequencies ( Fig. 6.1 ). Amplitude of the frequency components is important. A trace may have a very broad frequency band of reliable signal elements but those at low amplitudes can carry very little significant information. The frequency component must be restored to their original level if they are to provide the proper contribution of information to the seismic trace.
The process by which the attenuated elements are restored is another filter operation termed deconvolution. The theory and action of deconvolution can be explained by the use of a simple system model.