Objective Minimum Resolvable Temperature Difference Research Articles

Objective evaluation method for advance thermal imagers based on minimum resolvable temperature difference

Advancement in thermal imaging technology has improved the day and night surveillance capability of electro-optical system. Thermal imager detects the object of interest by sensing the temperature difference. The performance evaluation of these thermal imagers plays a vital role prior to effective deployment. Key performance parameter of thermal imaging system is minimum resolvable temperature difference (MRTD), as it is able to determine the overall system performance involving a human operator. MRTD is capable of defining the minimum temperature difference required to resolve the bar target pattern of defined spatial frequencies and provides the true estimate of the range performance of a thermal imaging system. In conventional methods, 4-bar target of defined resolution is exposed to the minimum resolvable condition to compute MRTD values. Presently, subjective MRTD measurement employs an operator to observe the minimum resolvable condition, and therefore, measurement suffers from poor repeatability. During large volume production, this practice becomes a tedious procedure to evaluate large numbers of thermal imaging sights. To ease the performance evaluation procedure, an objective MRTD measurement method for the evaluation of the thermal imaging system has been presented. In the present work, objective MRTD measurement method for advance thermal imager by computing the modulation transfer function and noise equivalent temperature difference has been presented. Experiments have been conducted to measure subjective and objective MRTDs. Results for both subjective and objective MRTD measurements have been compared and presented. It is found that the proposed method is able to produce very close result within accuracy of more than 95% than that of conventional methods.

Development and validation of a quantitative model for the subjective and objective minimum resolvable temperature difference of thermal imaging systems

The performance evaluation of infrared (IR) imaging systems plays a vital role prior to effective deployment. The minimum resolvable temperature difference (MRTD) is the primary key parameter of an IR imaging system, because it describes the overall system performance including that of a human operator. MRTD defines the minimum temperature difference required to resolve the four-bar target of defined spatial frequencies and is used to estimate the recognition ranges of a thermal imaging system before deployment for field evaluation. Conventionally, MRTD measurements use the temperature difference of a four-bar target that is exposed to the minimum resolvable condition. In current practice, subjective MRTD measurement employs a human operator to observe the minimum resolvable condition and therefore suffers from poor repeatability. It is a tedious procedure to evaluate large numbers of thermal imaging sights during production. In this work, an accurate objective MRTD measurement method is described by measuring the modulation transfer function and the noise equivalent temperature difference (NETD) of the thermal imager. Experiments were carried out to measure both subjective and objective MRTD. The results of the subjective and objective MRTD measurements are presented along with a comparison of the results. It is observed that the percentage error in objective MRTD is very close to that from a conventional subjective MRTD measurement.

Alternative measurement techniques for infrared sensor performance

This paper deals with measurement and characterization of IR sensor performance. Alternative methods have been investigated in order to determine the performance more reproducibly and accurately. Furthermore, the new methodologies reduce the subjectivity of the performance parameters such as the standard minimum resolvable temperature difference (MRTD) and tend to reduce the time (and thus cost) of measurement. The three methods described concern the use of (1) and IR zoom collimator, (2) a test device with line targets, and (3) an extended target combined with a TV camera instead of a human observer and a double-line source, resolving the ambiguity beyond the Ny-quist frequency in staring focal plane array cameras. In the IR zoom collimator a variety of targets are used in four different orientations; the observer has to report not only the recognition, but also the orientation of the target. Instead of variation of the temperature difference of the target, its range is varied by zooming in and out. In the rapid objective MRTD tester, the performance of the eye is simulated with a simple formula. The complete MRTD is obtained in about two minutes. In the double-slit method the best phase of the detector matrix is taken in comparison with the two line sources; instead of the MRTD curve, a new type of performance curve is measured: The minimum resolvable intensity difference (MRID), from which the range performance is obtained similarly to the classical MRTD method. The paper contains examples of measurements with each of the methods. ©2003 Society of Photo-Optical Instrumentation Engineers.

An objective MRTD for discrete infrared imaging systems

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 analysis, 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.