TOD performance theoretical model for scanning infrared imagers

Abstract

Since the triangle orientation discrimination threshold (TOD) measure was proposed, good progress has been made in some aspects, such as experimental validation, field performance, and TOD sensor performance model. However, what is still missing is a TOD curve prediction model similar to the minimum resolvable temperature difference (MRTD) equation. In this paper, an equation-based TOD performance model was first developed for scanning thermal imagers. Specifically, the spatial distribution of the triangle standard test pattern is described quantitatively. The resolution transfer characteristic of the scanning infrared imagers is modeled with linear system theory, and system noise is characterized by introducing a three-dimensional noise model. The modulation effect of overall subsystems of scanning thermal imager on the non-periodic standard triangle pattern is analyzed. The matched filter idea is adopted to characterize quantitatively the spatial–temporal integration of the human visual system to signal and various noise components over the triangle pattern area, and the perceived signal-to-noise ratio for the scanning infrared imager is derived. From this, a TOD performance theoretical model is established. Comparisons with experimental results show that this theoretical model gives reasonable prediction of the TOD performance curve for scanning thermal imagers. Although more tests and modifications are required, these preliminary results suggest that this model can be developed into a model that predicts the TOD for all kinds of sensors.