Point source sensitivity (PS sensitivity) is a determination of how sensitive an instrument is to detecting a point source. For instruments such as CCDs with pixels, it can be a statistically-based quantity based upon signal-to-noise ratio threshold aiming to separate actual sources from random noise (e.g., photon noise): in actuality, such a threshold only produces a probability of a point source. Different thresholds might be used for confirming or measuring a point source versus discovering one. For radio telescopes and radio interferometers, I think such sensitivities might be calculated but there could be differences. Surface brightness sensitivity is a similar analysis of an instrument's ability to determine surface brightness.