An ultrasonic sensor assembly detects a characteristic of a pipe. The ultrasonic sensor assembly includes first and second transducer rings spaced apart along a length of the pipe. Each of the first and second transducer rings can transmit a first wave longitudinally along the pipe and receive a reflection of the transmitted first wave from the characteristic. The first transducer ring can use results related to the reflection of the transmitted first wave to guide a second wave along the pipe that is received by the second transducer ring. Methods of detecting a characteristic of the pipe are also provided.