| 摘要 |
In order to prevent late arriving and higher amplitude shear waves from saturating the subsurface amplifier, the amplitude of each succeeding positive half cycle of the earlier arriving compressional wave is measured and a negative feedback is supplied to the amplifier if the measured amplitude exceeds 50% of full scale. Circuitry is provided for utilization of a two transmitter, two receiver system using the same type of negative feedback to control the gain of the subsurface amplifier.
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