Staring imager minimum resolvable temperature measurements beyond the sensor half sample rate

It is a well-known phenomenon that three- and four-bar patterns can sometimes be resolved with staring sensors even when the bar pattern frequency is beyond the half sample rate of the sensor. When performing a minimum resolvable temperature (MRT) test, for example, the modulation of the target bars can be significant even when the fundamental frequency of the four-bar target is higher than the half sample rate of the sensor. We show that the modulation of a four-bar target goes to zero at 0.6 times the sample rate of the sensor (1.2 times the half sample rate) if the sample phasing is optimized. If the bar pattern contains a larger number of bars, the modulation cutoff approaches the half sample rate of the sensor. Further, we illustrate that, when the sample phase is optimized during the MRT measurement, the MRT performance of a sampled imager can exceed the measured MRT performance of an analog sensor with the same system and component modulation transfer functions.