Seismic systems for investigating subterranean conditions

Claim 1

IN A SYSTEM FOR OBTAINING SIMULTANEOUSLY A FORWARD AND REVERSE SEISMIC PROFILE OF SUBTERRANEAN LOCATION. A FIRST AND SECOND SOUND SOURCE; A MULTIPLICITY OF SOUND RECEIVERS EQUALLY SPACED THEREBETWEEN; MEANS FOR MOVING SAID SOUND SOURCES AND SAID SOUND RECEIVERS OVER SAID LOCATION; MEANS FOR ACTIVATING SAID FIRST SOUND SOURCE AT SAID TIMES T1, T3, T5, ETC., AND SAID SECOND SOUND SOURCE AT TIMES T2, T4, T6, ETC., A SELECTOR SWITCH HAVING A PLURALITY OF INPUT CIRCUITS AND A SINGLE OUTPUT CIRCUIT; A FIRST AND SECOND RECORDER; MEANS FOR COUPLING EACH OF SAID SOUND RECEIVERS TO A DIFFERENT INPUT CIRCUIT OF SAID SELECTOR SWITCH; MEANS FOR ADVANTAING SAID SELECTOR SWITCH AT TIMES T1, T3, T5, ETC., TO DIFFERENT POSITIONS THEREBY TO CONNECT EACH OF SAID INPUT CIRCUITS TO SAID OUTPUT CIRCUIT; AND MEANS FOR COUPLING THE OUTPUT CIRCUIT OF SAID SELECTOR SWITCH TO SAID FIRST AND SECOND RECORDERS DURING MUTUALLY EXCLUSIVE TIME INTERVALS WHEREBY SAID FIRST RECORDER REGISTERS SOUND PULSES ORIGINATING AT SAID FIRST SOUND SOURCE AND SAID SECOND RECORDER REGISTERS SOUND PULSES ORIGINATING AT SAID SECOND SOUND SOURCE.