Range performance model TRM4

The TRM software has been in continuous development for several years. While first versions were limited to modeling of thermal imagers, TRM4.v1 and later versions allow for the performance evaluation of electro-optical systems in the visible to the thermal infrared spectrum. Supported observation scenarios are, apart from the horizontal view, the flyby and approach to an object as well as the observation of objects against the sky. The user can individually specify all components along the imaging chain – starting with the scene, through the atmosphere, optics, sensor and signal processing to the display and the observer. To support the user, the TRM4 software contains a library of generic, spectrally resolved data for lighting sources, object and background reflectivities, detector sensitivities and much more.

In addition to the detection, recognition and identification ranges, a large number of other performance parameters are calculated in TRM4. They support the user in understanding the properties of the electro-optical system as well as the performance-limiting factors and components. Examples for these performance parameters are the figures of merit of the overall system MTDP (Minimum Temperature Difference Perceived) and MCP (Minimum Contrast Perceived), the MTFs (Modulation Transfer Functions) of all system components, the detected signal as well as the temporal and non-uniformity noise. As of version TRM4.v3, the user can assess the quality of aerial images for the specified imaging system by means of the calculated NIIRS values ​​(National Imagery Interpretability Rating Scale).

Fraunhofer IOSB distributes the TRM4 software with a graphical user interface free of charge to licensees. In addition, customer-specific TRM4 versions are offered that can be integrated into user applications or used in batch mode. You can find further information at „Obtaining a license for TRM4“ and „Customized TRM4 Batch Module“.

The range performance calculation in TRM4 is based on modified Johnson criteria. Here, actual targets are replaced by equivalent bar patterns, as shown in the figure. The size, number of line pairs, and signal difference of the equivalent bar pattern depends on the target and the perception task (typically detection, recognition, and identification). The range performance is then determined as the maximum target-observer distance at which the observer can perceive the modulation of the equivalent bar pattern.

Range performance assessment in TRM4 is closely connected to the MTDP (Minimum Temperature Difference Perceived) figure of merit of thermal imagers. The MTDP is the minimum temperature difference that allows an observer to resolve a standard 4-bar pattern at given spatial frequency. Measured MTDP values may be used as input in TRM4 for the range performance calculation as well as TRM4 can predict the MTDP of thermal imagers. The comparison of measured and calculated MTDP is used at Fraunhofer IOSB to validate TRM4.

For more in-depth information on the TRM4 evaluation procedure, please refer to the infoboxes attached below.

TRM4 is one of the core components of ECOMOS (European Computer Model for Optronic System Performance Prediction). ECOMOS is a novel evaluation approach, which in the long run should also allow to evaluate the influence of advanced digital signal processing techniques on the performance of optronic systems. More information about the European ECOMOS project can be found in the corresponding publication and the ECOMOS Homepage.