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' The sensors were calibrated after optimum acoustic coupling to the tank was <br /> confirmed. Calibration of each sensor and its associated data channel was <br /> ' performed to within one decibel sensitivity by using an acoustic source signal <br /> input at a position one foot from each sensor. this acoustic source was used <br /> to verify the same relative response for each sensor before and after testing. <br /> Velocity of sound in the tank was also determined prior to testing by <br /> measuring diametric travel time of an acoustic pulse across the tank. <br /> After all sensors were emplaced and calibrated and the tank-specific sound <br /> ' velocity was measured, testing operations commenced. The acoustic monitoring <br /> was continued for a period of six hours, during which time all raw data were <br /> ' recorded on magnetic tape and sensor responses were monitored by the operator. <br /> Specific test parameters for each tank are presented in Table 1. <br /> 1 <br /> ' -6- <br />