3-System Setup Parameters
pulseEKKO PRO
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3.5.2 Gain Type Applied and Gain Applied
Since the radar signal strength normally decreases with increasing time, it is usually necessary to apply
some sort of gain function to boost the weaker signals at later times.
The raw, ungained data shows little signal except for the strong near-surface reflectors (Figure 3-15). No
gain may be useful in areas where the radar signal is very strong or in areas where the targets are very
shallow.
Four gains are available: AGC, SEC, Constant, and None. These are each described below.
No matter which gain function has been selected, the data are ALWAYS stored WITHOUT any gain
applied. Gain is only applied for real-time display purposes.
For data collection in the field, AGC and constant gains are often the most practical to show that the
system is working properly and to show a range of reflectors in the material. Other more sophisticated
gains, like SEC functions, can be applied later when plotting the data in the office.
Figure 3-15: Display of a data section over buried tanks. No gain was applied before plotting.
Note that none of the gain functions are permitted to boost a data point value to greater than 32767 or less
than -32767. Values where this occurs are trapped and forced to 32767 or -32767.
3.5.2.1
AGC Gain
The AGC (Automatic Gain Control) gain attempts to equalize all signals by applying a gain which is
inversely proportional to the signal strength (Figure 3-16). This type of gain is most useful for defining
continuity of reflecting events. The user should realize that AGC does not preserve relative amplitude
information. Hence once the data have been AGC'ed, the user can no longer make reliable deductions
concerning the strength of any particular reflector relative to other reflectors (Figure 3-17).
Since the AGC gain is inversely proportional to the signal strength, very small signals can produce very
large gains. Therefore some type of gain limiting scheme must be applied. The user enters the maximum
gain which can be applied to the data. This maximum gain is then fixed for the whole data set.
Note that if a data point multiplied by the gain exceeds 32767, the absolute value of the new data point
value becomes 32767 or -32767.
