What could lead to an increase in the noise level during ultrasonic testing?

The presence of surface roughness is indeed a factor that can lead to an increase in noise levels during ultrasonic testing. Surface roughness can scatter ultrasonic waves, which can create a greater number of reflections and diffracted waves. This scattering results in a higher level of background noise, making it more challenging to identify and interpret the signals related to defects or material characteristics.

When ultrasonic waves encounter a rough surface, instead of producing a clear and direct reflection that can be interpreted, the signal gets distorted and scattered in various directions. This scattering introduces noise, which can mask the echoes returned from any flaws or discontinuities in the material. Thus, surface conditions play a critical role in the effectiveness and clarity of ultrasonic testing signals.

In contrast, while other factors listed may influence the testing process in other ways, they do not directly contribute to an increase in noise levels in the same manner as surface roughness does.