Dual-spaced acoustical well logging system

Claim 1

AN ACOUSTIC WELL LOGGING SYSTEM COMPRISING SURFACE RECORDING MEANS, A SUBSURFACE INSTRUMENT, AND A LOGGING CABLE INTERCONNECTING SAID INSTRUMENT AND SAID RECORDING MEANS, SAID INSTRUMENT FURTHER INCLUDING A TRANSMITTER ARRANGED AND ADAPTED TO GENERATE ACOUSTIC PULSES, A TRANSMITTER ACTUATOR ARRANGED AND ADAPTED TO PERIODICALLY ACTUATE SAID TRANSMITTER AT A PRESELECTED FREQUENCY, A FIRST RECEIVER MEANS SPACED A FIRST DISTANCE FROM SAID TRANSMITTER, A SECOND RECEIVER MEANS TRAILINGLY SPACED FROM SAID TRANSMITTER AND SAID FIRST RECEIVER MEANS A PREDETERMINED SECOND DISTANCE FROM SAID FIRST RECEIVER MEANS, A THIRD RECEIVER MEANS TRAILINGLY SPACED FROM SAID TRANSMITTER AND SAID FIRST AND SECOND RECEIVER MEANS A THIRD PREDETERMINED DISTANCE FROM SAID SECOND RECEIVER MEANS WHICH IS TWICE SAID SECOND PREDETERMINED DISTANCE, SIGNAL GENERATING MEANS HAVING TWO INPUTS AND HAVING AN OUTPUT CONNECTED TO SAID LOGGING CABLE, MEANS CONNECTING SAID FIRST RECEIVER MEANS TO ONE OF SAID TWO INPUTS OF SAID SIGNAL GENERATING MEANS, SWITCH MEANS RESPONSIVE TO ACTUATION OF SAID TRANSMITTER ACTUATOR FOR ALTERNATELY CONNECTING AND DISCONNECTING SAID SECOND AND THIRD RECEIVER MEANS TO AND FROM THE OTHER OF SAID TWO INPUTS OF SAID SIGNAL GENERATING MEANS UPON RESPECTIVE ALTERNATE ACTUATIONS OF SAID TRANSMITTER, AND GATING MEANS RESPONSIVE TO ACTUATION OF SAID TRANSMITTER TO RENDER SAID SIGNAL GENERATING MEANS RESPONSIVE TO SAID FIRST RECEIVER MEANS AND SAID ONE OF SAID SECOND AND THIRD RECEIVER MEANS.