Digital acoustic logging method and apparatus

DETAILED DESCRIPTION The method and apparatus for processing a received analog signal in accordance with the present invention utilizes a sample and storage device that sequentially samples the amplitude values of a real time portion of the received signals and then subsequently reads the values out over an expanded period of time.
In a preferred embodiment of the invention, the expanded output is amplified by an automatic gain controlled (AGC) amplifier.
The AGC signal is determined by reading a portion of the stored values and determining either the rms value thereof or a peak value of such portion.
Since the expanded output is a delayed reading, there is ample time for developing the AGC signal before the amplification is required.
In a preferred embodiment application of the above, the recognition of the compression wave is assured for purposes of determining its arrival time and measuring its amplitude by way of a convolving scheme.
First, the wave arrival is approximated.
This is done by measuring the rms value of the inherent noise before the compression wave arrival, adding a value thereto, and detecting the first three successive samples greater than this value that follow such nominal-noise time period.
The first of the three samples is then assumed to be the approximate onset of the compression wave.
This presumed compression wave is stored and then convolved against the expanded-time digitally sampled and stored signal from a second receiver as described above until the compression wave is indicated.
Further convolving results in identification and location of the "shear" wave.