Lingfeng Chen

Analysis for MRTD and DMRTD based on contrast simulation

Due to the phasing effects, the measurements of Minimum Resolvable Temperature Difference (MRTD) for Staring array thermal imagers often get abnormal results when the targets approaching system Nyquist frequency (fn). To simulate the relations between MRTD values and four-bar targets frequencies, this paper introduces the concept of best contrast. Clearly, the MRTD results are inversely proportional to the best contrasts under optimum phases, higher contrast corresponding to a lower MRTD. On the other hand, with the spatial frequencies increasing, the targets opening area shrinking and leads the effective infrared eradiation decreasing, this means the MRTD results are inversely proportional to the opening area of the target. Based on these two assumptions, and through numerical simulations, this paper depicts the tendency chart of MRTD under optimum phases to the four-bar targets spatial frequencies. The tendency chart adequately explains the hump curve happens at frequencies between 0.6fn and fn. From the simulations, the maximum of MRTD values can be predicted at the frequency of 0.89fn. The tendency chart illustrated by numerical simulation is consistent with the MRTD results get in laboratory. While in Dynamic Minimum Resolvable Temperature Difference (DMRTD) testing, moving the four-bar targets introduces temporal effects not present in static MRTD test. Simulation reveals that DMRTD test can get more realistic shape of the curve between 0.6fn and fn, the characteristic hump in the static MRTD curve between 0.6fn and fn is not seen.