An objective method has been developed for measuring the minimum resolvable temperature difference (MRTD) of infrared imaging systems employing focal plane detector arrays. The resulting MRTD is uniquely determined by applying discrete Fourier transform techniques, thus avoiding the previous multi-valued problem associated with the non-isoplanatic property of discrete devices. The derivation is based on sinusoidal wave input targets but a practical measuring procedure has been developed using conventional bar patterns; alternatively the MRTD may be calculated by measuring the MTF using the line spread function. This objective MRTD has also been compared with conventional subjective measurements.
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