In straight beam pulse echo testing, how does a discontinuity with a rough reflecting surface affect the detected signal compared to a smooth flat-bottom hole?

A discontinuity with a rough reflecting surface affects the detected signal by decreasing its amplitude compared to a smooth flat-bottom hole. In straight beam pulse echo testing, the characteristics of the reflecting surface play a crucial role in how ultrasonic waves are reflected and returned to the transducer.

When ultrasonic waves encounter a smooth flat-bottom hole, the surface reflects the waves uniformly, resulting in a strong, well-defined echo signal. The smoothness allows for efficient transmission of sound waves with minimal scattering, which maximizes the amplitude of the reflected signal and creates a clear indication of the discontinuity.

In contrast, a rough reflecting surface scatters the ultrasonic waves in various directions rather than reflecting them back directly to the transducer. This scattering causes a loss in the amplitude of the returning signal, leading to a weaker echo that may be harder to detect. The irregularities on the surface disrupt the coherent reflection of sound waves, which ultimately results in a decrease in the strength of the detected signal.

Therefore, the presence of a rough discontinuity means that the detected signal will be less intense when compared to the signal reflected from a smooth surface, which is why the correct choice indicates a decrease in the signal.