Main performance parameters of infrared thermal imaging systems

The complete thermal imaging process is: the infrared radiation of the scene in the three-dimensional space is projected onto the infrared focal plane array through the infrared optical system, and the infrared focal plane array is converted into a one-dimensional time-distributed electrical signal output, after subsequent signal processing, and finally The two-dimensional spatially distributed visible light signal reproduces the infrared radiation field of the scene. In this process, each aspect of the scene radiation characteristics, atmosphere, an optical system, focal plane array, electrical part, display, the human eye, etc. will affect the imaging performance.

The history of performance evaluation models dates back to the 1970s. The US Night Vision Lab established the NVL75 performance evaluation model, which is suitable for the first generation of infrared imaging systems. It can make better predictions for medium-space frequency targets and meet the requirements of the US military at that time. With the advent of focal plane array devices, the FLIR92 model has emerged. It introduces a three-dimensional noise model, which fully characterizes all noise sources, makes the fusion of complex noise factors and MRTD model formulas simple, and can predict the static performance of scanning or staring infrared imaging systems. The NV Therm and TRM3 models have also appeared in recent years.

The performance of the thermal imaging system mainly includes static performance and dynamic performance. The static performance describes the imaging capability of the system to static targets, that is, the three-dimensional spatial distribution of the scene does not change with time, and the dynamic performance describes the imaging capability of the system for dynamic targets. Thermal imaging system performance parameters usually refer to the system's laboratory testable parameters, such as noise equivalent temperature difference (NETD), the minimum resolvable temperature difference (MRTD), the modulation transfer function (MTF), etc., which can be further extended to the system's range of action. The imaging quality of infrared thermal imaging systems must have an objective evaluation method. Usually, we use a variety of characteristic parameter tests to evaluate the infrared thermal imaging system. These characteristic parameters include noise and response characteristics, image resolution characteristics, image geometric characteristics, personal subjective characteristics and other parameters, the details of which are shown in Table 14.1. The characteristic parameters of the commonly used infrared thermal imaging system are noise equivalent temperature difference (NETD), modulation transfer function (MTF), and minimum resolvable temperature difference (MRTD).

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