Changes

The choice of the design windows for the AGC affects the display. If the window is very short in time, the program tends to raise all amplitudes to the standard and very little differentiation between events is preserved. Generally, a window of about 250 msec is a good place to start. As the gate becomes longer, more of the original amplitude relationships are preserved. A single window trace equalization is sometimes desirable in processing data intended for relative amplitude studies, while a fast (short) AGC could be helpful in data having poor signal to noise ratio.

The choice of the design windows for the AGC affects the display. If the window is very short in time, the program tends to raise all amplitudes to the standard and very little differentiation between events is preserved. Generally, a window of about 250 msec is a good place to start. As the gate becomes longer, more of the original amplitude relationships are preserved. A single window trace equalization is sometimes desirable in processing data intended for relative amplitude studies, while a fast (short) AGC could be helpful in data having poor signal to noise ratio.

Another method of gaining the section is '"programmed gain control'". This method applies a predetermined gain function to the trace and is most commonly encountered in field displays.

Another method of gaining the section is programmed gain control. This method applies a predetermined gain function to the trace and is most commonly encountered in field displays.

Since some form of gain is required to display the data at a usable scale, what are often called ''true amplitude'' sections are in reality relative true amplitude sections. The relative changes in amplitude are preserved by the method of gain used, and yet the entire data set is interpretable from the same display.

Since some form of gain is required to display the data at a usable scale, what are often called ''true amplitude'' sections are in reality relative true amplitude sections. The relative changes in amplitude are preserved by the method of gain used, and yet the entire data set is interpretable from the same display.

''Filtering'', that is, limiting the frequency content of the display, is an important aspect of the final display. A certain amount of filtering is done during the processing sequence to enhance the signal to noise ratio. At display time, one has a final opportunity to choose the frequency band that highlights the seismic target best. This highly subjective decision is usually made by testing several ranges and then choosing the one that works for that particular play. Usually the useful band width for the shallow section is much greater than for the deep section. Noise content may also vary with time and position along the line. A wide variety of constant or time/distance varying filter techniques is available.

Filtering, that is, limiting the frequency content of the display, is an important aspect of the final display. A certain amount of filtering is done during the processing sequence to enhance the signal to noise ratio. At display time, one has a final opportunity to choose the frequency band that highlights the seismic target best. This highly subjective decision is usually made by testing several ranges and then choosing the one that works for that particular play. Usually the useful band width for the shallow section is much greater than for the deep section. Noise content may also vary with time and position along the line. A wide variety of constant or time/distance varying filter techniques is available.

Frequently, the noise degrading the signal may be very similar to the signal in dip, frequency, and other properties. At this point, you may have to choose how much signal you are willing to give up to reduce or eliminate the noise.

Frequently, the noise degrading the signal may be very similar to the signal in dip, frequency, and other properties. At this point, you may have to choose how much signal you are willing to give up to reduce or eliminate the noise.