What term describes the ability of an ultrasonic testing system to distinguish between the entry surface response and the response of discontinuities near the entry surface?

The term that best describes the ability of an ultrasonic testing system to distinguish between the entry surface response and the response of discontinuities near the entry surface is resolution.

Resolution in ultrasonic testing refers to the system's capability to distinguish between two closely spaced echoes or signals. This characteristic is vital for accurately identifying and characterizing discontinuities within a material. When resolution is high, a technician can differentiate between reflections from the entry surface and those from flaws or features close to that surface, allowing for a more accurate assessment of the material's integrity.

Clarity generally refers to the overall sharpness or vividness of an image but does not specifically address the system's ability to differentiate between close signals. Contrast often relates to the difference between light and dark in an image, which is more about visual perception than the technical measurement of responses in ultrasonic testing. Definition, while it may sound relevant, is not a standard term used in NDT to describe the capability of distinguishing echoes.

Therefore, resolution is the most precise term in this context, as it directly pertains to the effective separation of signals and the quality of the ultrasonic testing results.