Accurate and fast stray radiation calculation based on improved backward ray tracing

Abstract

An improved method of backward ray tracing is proposed according to the theory of geometrical optics and thermal radiation heat transfer. The accuracy is essentially raised comparing to the traditional backward ray tracing because ray orders and weight factors are taken into account and the process is designed as sequential and recurring steps to trace and calculate different order stray lights. Meanwhile, it needs very small computation comparing to forward ray tracing because irrelevant surfaces and rays are excluded from the tracing. The effectiveness was verified in the stray radiation analysis for a cryogenic infrared (IR) imaging system, as the results coincided with the actual stray radiation irradiance distributions in the real images. The computation amount was compared with that of forward ray tracing in the narcissus calculation for another cryogenic IR imaging system, it was found that to produce the same accuracy result, the computation of the improved backward ray tracing is far smaller than that of forward ray tracing by at least 2 orders of magnitude.

Calibration Method for Airborne Infrared Optical Systems in a Non-Thermal Equilibrium State

“…When the system is in State (a), the expression for stray radiation is provided by Equation (10). In this state, the optical temperature of the system is equivalent to the ambient temperature.…”

“…Many studies have investigated the impact of internal stray radiation on the detector response in infrared systems. During the system design, the common approach is to construct an analysis model to assess the influence of internal stray radiation [ 8 , 9 , 10 , 11 ]. Analysis software such as TracePro, Lighttools, ASAP, FRED, and others are commonly used for simulation estimation.…”

Accurate and fast narcissus calculation based on sequential ray trace

“…2(b), then calculate the h img and h sto values of each retro-reflected ray using Eqs. (4,5), and after that carry out the judgement criteria expressed as Eq. (1).…”

“…• Nonsequential ray trace, which traces bundles of rays from the detector to the retro-reflecting surface and counts the number of rays reflected back to the detector, then calculates the narcissus introduced equivalent temperature (NITD) [4,5]. The advantage is that the accuracy is high and the narcissus distribution on the full field of view can be obtained; the disadvantage is that it often needs extra modeling and the whole process usually takes a long time.…”