Minimum Resolvable Temperature Difference Research Articles

Dung Beetle Optimized Fuzzy PID Algorithm Applied in Four-Bar Target Temperature Control System

With the widespread application of infrared thermal imagers in various fields, the demand for thermal imagers and their performance parameter testing equipment has increased significantly. There are particularly high demands on the detection accuracy of minimum resolvable temperature difference (MRTD) testers. Traditional MRTD testers have an issue with the four-bar target temperatures being easily affected by the external environment, resulting in non-uniform temperatures and imprecise detection results. This paper proposes an improvement to the four-bar targets by making them temperature-controllable. Temperature is controlled by installing thermoelectric coolers (TECs) and thin-film platinum resistors at the center and periphery of the four-bar targets with different spatial frequencies. The dung beetle algorithm is used to optimize fuzzy PID parameters to regulate the TEC’s heating and cooling, improving the overall temperature uniformity of the four-bar targets. Temperature simulations of the four-bar targets were conducted on the COMSOL platform, with the control part simulated on the Simulink platform. The simulation results show that, compared to traditional PID, the fuzzy PID controller reduces overshoot by approximately 3.6%, although the system still exhibits mild oscillations. The fuzzy PID controller optimized by the dung beetle optimization (DBO) algorithm, in comparison to standard fuzzy PID, reduces the settling time by about 40 s and lowers overshoot by around 7%, with oscillations in the system nearly disappearing. Comparing the fuzzy PID optimized by the particle swarm optimization (PSO) algorithm with the fuzzy PID optimized by the DBO algorithm, the DBO-based controller shows shorter rise and settling times, further illustrating the superiority of the fuzzy PID control optimized by the dung beetle algorithm. This provides a theoretical foundation for improving the accuracy of MRTD detector measurements. Finally, experimental verification was carried out. The experimental results indicate that DBO (drosophila-based optimization) has significant advantages, and its optimized results are closer to the actual values.

Multiscale Deblurred Feature Extraction Network for Automatic Four-Rod Target Detection in MRTD Measuring Process of Thermal Imagers.

The minimum resolvable temperature difference (MRTD) at which a four-rod target can be resolved is a critical parameter used to assess the comprehensive performance of thermal imaging systems, which is important for technological innovation in military and other fields. Recently, there have been some attempts to use an automatic objective approach based on deep learning to take the place of the classical manual subjective MRTD measurement approach, which is strongly affected by the psychological subjective factors of the experimenter and is limited in accuracy and speed. However, the scale variability of four-rod targets and the low pixels of infrared thermal cameras have turned out to be a challenging problem for automatic MRTD measurement. We propose a multiscale deblurred feature extraction network (MDF-Net), a backbone based on a yolov5 neural network, in an attempt to solve the aforementioned problem. We first present a global attention mechanism (GAM) attention module to represent strong images of the four-rod targets. Next, a Rep VGG module is introduced to decrease the blur. Our experiments show that the proposed method achieves the desired effect and state-of-the-art detection results, which innovatively improve the accuracy of four-rod target detection to 82.3% and thus make it possible for the thermal imagers to see further and to respond faster and more accurately.

Spatial-noise subdivision evaluation model of uncooled infrared detector

In this study, a spatial-noise subdivision evaluation model of an infrared detector is introduced. The spatial noise was classified into five independent noise components according to their graphic features. A frequency domain analysis method was used to accurately separate the spatial noise components and calculate their spatial noise equivalent temperature difference. By testing the spatial noise components of the mainstream uncooled infrared detector, we found that the main components were high and low spatial frequency noise. The effects of spatial noise on the performance of the infrared system were also analyzed for two typical applications of imaging and temperature measurements. We found that spatial high-frequency noise is the main factor affecting the minimum resolvable temperature difference performance of the infrared imaging system, whereas spatial low-frequency noise is the main factor affecting the accuracy of temperature measurements in the infrared temperature measurement system. The results indicate directions for further studies on the spatial noise of uncooled infrared detectors.

Measurement and Analysis of the Parameters of Modern Long-Range Thermal Imaging Cameras.

Today’s long-range infrared cameras (LRIRC) are used in many systems for the protection of critical infrastructure or national borders. The basic technical parameters of such systems are noise equivalent temperature difference (NETD); minimum resolvable temperature difference (MRTD); and the range of detection, recognition and identification of selected objects (DRI). This paper presents a methodology of the theoretical determination of these parameters on the basis of technical data of LRIRCs. The first part of the paper presents the methods used for the determination of the detection, recognition and identification ranges based on the well-known Johnson criteria. The theoretical backgrounds for both approaches are given, and the laboratory test stand is described together with a brief description of the methodology adopted for the measurements of the selected necessary characteristics of a tested observation system. The measurements were performed in the Accredited Testing Laboratory of the Institute of Optoelectronics of the Military University of Technology (AL IOE MUT), whose activity is based on the ISO/IEC 17025 standard. The measurement results are presented, and the calculated ranges for a selected set of IR cameras are given, obtained on the basis of the Johnson criteria. In the final part of the article, the obtained measurement results are presented together with an analysis of the measurement uncertainty for 10 LRIRCs. The obtained measurement results were compared to the technical parameters presented by the manufacturers.

Development and application of infrared imaging check and evaluation system

According to the parameters of various kinds of infrared imaging equipment was performance full automatic detection and evaluation of research in this paper. The evaluation system will to accuracy, slit function (SRF), minimum resolvable temperature difference (MRTD), minimum detectable temperature difference (MDTD) and noise equivalent temperature difference (NETD) and other parameters as the basis, the establishment of infrared imaging evaluation system database, to convergence of digital interface to realize automatic detection and evaluation of infrared imaging device, solving the technical problem of performance evaluation of grid infrared imaging equipment, ensure the accuracy of condition based maintenance for power transmission system.

Research on Performance Evaluation and Optimization Theory for Thermal Microscope Imaging Systems

Infrared imaging theory is an important theoretical basis for the design of infrared imaging systems, but there is no research on infrared imaging theory for designing thermal microscope imaging systems. Therefore, we studied the performance evaluation and optimization theory of thermal microscope imaging systems. In this paper, we analyzed the difference in spectral radiant flux between thermal microscope imaging and telephoto thermal imaging. The expression of signal-to-noise ratio of the output image of the thermal microscope imaging systems was derived, based on the analysis of the characteristics of thermal microscope imaging. We studied the performance evaluation model of thermal microscope imaging systems based on the minimum resolvable temperature difference and the minimum detectable temperature difference. Simulation and analysis of different detectors (ideal photon detector and ideal thermal detector) were also carried out. Finally, based on the conclusion of theoretical research, we carried out a system design and image acquisition experiment. The results show that the theoretical study of thermal microscope imaging systems in this paper can provide reference for the performance evaluation and optimization of thermal microscope imaging systems.

Trade-off Optimization Method for Infrared Imaging System Based on Modification of λF/d

The precise matching of the optical system and the detector has attracted more and more attention to satisfy requirements of future infrared (IR) imaging systems, both for miniaturization and long-distance detection. Considering the trade-off between the spatial resolution and the sensitivity, this paper proposes a general optimization method, which can optimize parameters of the IR imaging system automatically by modifying $\lambda \text{F}$ /d. Firstly, on the basis of the trade-off between the spatial transfer characteristics and the spatial sampling characteristics, we establish a more accurate minimum resolvable temperature difference (MRTD) model, and analyze the coupling relationship between the optical system and the detector under the optimum MRTD. Secondly, we analyze the relationship between parameters of the IR imaging system and MRTD model, and propose a trade-off optimization approach of the IR imaging system. Finally, this paper verifies the rationality of the optimization method by optimizing CA-295 system. The trade-off optimization method proposed in this paper can not only satisfy the design requirement, but also reduce the size, weight, power consumption and cost (SWaP$) of IR imaging systems.

Design of airborne dual-band common aperture photoelectric aiming optical system

Aiming at the problem of central obstruction and assembly difficulties in the reflective imaging of the airborne dual-band common-aperture photoelectric sighting system, a common-aperture optical system with front-light path refraction imaging was designed. The initial structure of the optical system was calculated using the two-component zoom theory. Based on the Minimum Resolvable Temperature Difference (MRTD) model, the operating distance of infrared system was analyzed, and the compensation residual error of forward image motion was analyzed according to Rayleigh criterion. When the airborne dual-band common-aperture photoelectric aiming optical system worked in the waveband of 0.38-0.76 μm, it can achieve 5× continuous zoom from 36 to 180 mm. When it worked in the 3-5 μm waveband, it can realize three fields of view transformations, and the ratio of the three focal lengths of the three fields is 3. The working F number was 4. The design results show that, in the working environment of −40-60 ℃, the optical system undergoes optical passive athermalization treatment, which meets the requirements of system imaging quality.

CALCULATION OF OBJECTS THERMAL IMAGING PARAMETERS FROM UNMANNED AERIAL VEHICLES

This article is aimed at studying the influence of the entire complex parameters on the characteristics of the obtained thermal images when shooting the Earth’s surface from unmanned aerial vehicles. The values of the minimum detectable and minimum resolvable temperature differences are calculated depending on the parameters of the thermal imager, the survey and the size of the object (spatial frequency) for three serial miniature thermal cameras used in aerial surveys of the Earth's surface from unmanned aerial vehicles. Analytical formulas for estimating the minimum resolvable temperature difference are obtained on the basis of a mathematical model of the thermal imager as a linear system of individual components based on the technique that differs from the generally accepted one. Estimates were made for two cases: observation of a thermal image by an operator on a display screen and for the case when an electronic image is analyzed by a threshold algorithm with no operator engaged. For the first time, the influence of the carrier velocity on the overall modulation transfer function of the system and, accordingly, the temperature and spatial resolution of thermal imagers was taken into account. The main components that must be considered when calculating the full modulation transfer function of the system are: a thermal imager lens, a radiation detector, carrier movement and the observer's visual system. Moreover, the parameters of the detector and the speed of the carrier have the greatest influence on the temperatures resolvable by the system.

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.

Virtual MRTD – an indirect method to measure MRTD of thermal imagers using computer simulation

Minimum resolvable temperature difference (MRTD) is considered as the most important parameter of thermal imagers. A new method of MRTD measurement without drawbacks of other methods is presented in this paper. Proposed MRTD measurement method coded as virtual MRTD is based on a three steps measurement concept using semi-automatic objective measurements and computer simulation. First, objective parameters of the tested thermal imager are measured. Second, software simulates this tested thermal imager and generates the image of 4-bar target of specified spatial frequency (size) and contrast (temperature difference). Third, a human observer analyses the images of the 4-bar target generated by the software on the screen of PC set and measures MRTD of the simulated thermal imager at specified set of spatial frequencies. The proposed method offers higher measurement speed, lower cost and typically better accuracy in comparison with the typical MRTD measurement method.

Focus on lasers, imaging, and microscopy

Focus on lasers, imaging, and microscopy

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.

Focus on test, measurement, software, and instrumentation

Focus on test, measurement, software, and instrumentation

Minimum detectable gas concentration performance evaluation method for gas leak infrared imaging detection systems.

Thermal imaging technology is an effective means of detecting hazardous gas leaks. Much attention has been paid to evaluation of the performance of gas leak infrared imaging detection systems due to several potential applications. The minimum resolvable temperature difference (MRTD) and the minimum detectable temperature difference (MDTD) are commonly used as the main indicators of thermal imaging system performance. This paper establishes a minimum detectable gas concentration (MDGC) performance evaluation model based on the definition and derivation of MDTD. We proposed the direct calculation and equivalent calculation method of MDGC based on the MDTD measurement system. We build an experimental MDGC measurement system, which indicates the MDGC model can describe the detection performance of a thermal imaging system to typical gases. The direct calculation, equivalent calculation, and direct measurement results are consistent. The MDGC and the minimum resolvable gas concentration (MRGC) model can effectively describe the performance of "detection" and "spatial detail resolution" of thermal imaging systems to gas leak, respectively, and constitute the main performance indicators of gas leak detection systems.

The Study on the MRTD Measurement System of Medical Infrared Thermal Imager Based on Sub-Pixel Edge Detection Algorithm

MRTD (minimum resolvable temperature difference) is an important parameter to evaluate the infrared thermal imager. MRTD is not only related to the spatial resolution of the system, but also to many factors such as optical system, detector array and so on. The measurement technique and principle of the medical infrared thermal imager’s MRTD is deeply analyzed, and the MRTD measurement model is established in this paper. The MRTD measurement system of infrared thermal imager based on CCD imaging technology is designed. CCD is used to carry on the interpretation of temperature difference in this system instead of the human eye, which can avoid the effect of some factors on the subjective image quality evaluation, such as the contrast, the human interference flaw and so on. The sub-pixel edge detection algorithm is used to deal with the four-bar target image, which can effectively suppress the interface of the random noise on four-bar target image. The experimental results show that the MRTD testing accuracy of the system can reach 0.055℃.

Minimum resolvable temperature difference model, simulation, measurement and analysis

This paper proposes a mathematical model for numerical estimation of the MRTD. The developed model is based on a mathematical model designed to estimate the MRTD for 1st and 2nd generation thermal imagers which is modified to estimate the MRTD for 3rd generation thermal imagers. As a demonstration, the MRTD characteristic of three models of thermal imaging cameras is obtained numerically, then, the obtained MRTD values are compared with the measured values using the platform MS300 of Inframet.

海面环境中红外偏振成像系统作用距离模型

The fact that infrared radiation of sea surface is polarized has been proved by many experiments. Searching and detecting ability of infrared polarization imaging systems in sea-surface environment was a major concern for polarization imaging research. Sea surface was realized by using a statistical model of oceanographic literature which originated from the spectrum for long and short wind-driven waves proposed by Eifouhaily. A Monte Carlo reverse ray-tracing method was used to investigate the behavior of mid/long-wave infrared Stokes radiance which included the information of radiance intensity, degree of polarization and angle of polarization, at the realized wind roughed sea surface. The minimum resolvable temperature difference(MRTD) parameters for Stokes-vector components were proposed based on standard error propagation method. Finally, detectable range of infrared polarization imaging used in sea surface environment was analyzed by comparing apparent-temperature differences(ATD) between target and sea background with the MRTD of Stokes-vector components.

Model of thermal infrared image texture generation based on the scenery space frequency

Infrared texture is an important feature in identifying scenery. To simulate infrared image texture effectively at different distances, we propose a model of infrared image texture generation based on scenery space frequency and the image pyramid degradation principle. First, we build a spatial frequency filter model based on imaging distance, taking into account the detector’s maximum spatial frequency, and use the filter to process a “zero” distance infrared image texture. Second, taking into consideration the actual temperature difference of the scenery’s details due to variation of the imaging distance and the effect of atmospheric transmission, we compare the actual temperature difference with the minimum resolvable temperature difference of the thermal imaging system at a specific frequency and produce a new image texture. The results show that the simulated multiresolution infrared image textures produced by the proposed model are very similar (lowest mean square error=0.51 and highest peak signal-to-noise ratio=117.59) to the images captured by the thermal imager. Therefore, the proposed model can effectively simulate infrared image textures at different distances.

Equivalent-measurement evaluation method of minimum resolvable gas concentration

Currently, there is no standard method of evaluating the performance of the gas leak infrared imaging detection system. The evaluating criterions vary greatly and are deficient in aspects of completeness and accuracy, such as noise equivalent temperature difference, noise equivalent concentration path length, and minimum detectable leak rates. Minimum resolvable gas concentration (MRGC) is a latest proposed parameter for evaluating the performance of a passive gas leak infrared imaging detection system, which takes full advantage of the comprehensive evaluation capability of the temperature resolution and spatial resolution of the minimum resolvable temperature difference (MRTD) model. The MRGC takes into account the environmental and gas state parameters, the size of the gas plume and other factors which influence the MRGC measurement. However, the MRGC measurement system is complicated and many state parameters need to be controlled, especially the wide range and dedicated gas concentration meters are required. Therefore, the mathematical model of MRGC is derived and established. By comparing the principles and measurement methods of the performance parameters, MRGC and MRTD, a novel MRGC equivalent measurement evaluation method is proposed, on condition that the minimum resolvable radiation differences are equal. Using ethylene and ammonia as the target, the equivalently measured results of MRGC are obtained. The results show that the MRGC increases with the spatial frequency increasing and the smaller the temperature difference is between the gas and the background blackbody, the faster the MRGC increases. What is more, when the spatial frequency is fixed, MRGC increases with the gas temperature approaching to the background temperature. The background temperature varies asymptotically, which means that if the gas temperature equals the background temperature, the system cannot detect the gas four-bar pattern, no matter what the gas concentration is (here, the maximum gas concentration is 1 million ppm under normal pressure.). The directly measured and equivalently measured results of ethylene are in good agreement within errors of less than ±20%, and the maximum error is 18.26% at a spatial frequency of 0.214f0, which demonstrates the feasibility and effectiveness of the method. Because the equivalent measurement method only needs the traditional MRTD measurement results and the gas infrared spectrum database, it is simple and reliable, which is very significant for the study and application of the gas leak infrared imaging detection systems.