TRM4: Range performance model for electro-optical imaging systems

TRM4 is a commonly used model for assessing device and range performance of electro-optical imagers. The latest version, TRM4.v2, has been released by Fraunhofer IOSB of Germany in June 2016. While its predecessor, TRM3, was developed for thermal imagers, assuming blackbody targets and backgrounds, TRM4 extends the TRM approach to assess three imager categories: imagers that exploit emitted radiation (TRM4 category Thermal), reflected radiation (TRM4 category Visible/NIR/SWIR), and both emitted and reflected radiation (TRM4 category General). Performance assessment in TRM3 and TRM4 is based on the perception of standard four-bar test patterns, whether distorted by under-sampling or not. Spatial and sampling characteristics are taken into account by the Average Modulation at Optimum Phase (AMOP), which replaces the system MTF used in previous models. The Minimum Temperature Difference Perceived (MTDP) figure of merit was introduced in TRM3 for assessing the range performance of thermal imagers. In TRM4, this concept is generalized to the MDSP (Minimum Difference Signal Perceived), which can be applied to all imager categories. In this paper, we outline and discuss the TRM approach and pinpoint differences between TRM4 and TRM3. In addition, an overview of the TRM4 software and its functionality is given. Features newly introduced in TRM4, such as atmospheric turbulence, irradiation sources, and libraries are addressed. We conclude with an outlook on future work and the new module for intensified CCD cameras that is currently under development.