This chapter presents an overview of the computer programs Thermal and Reflective. Both programs have help files that describe individual inputs. This chapter does the following:
1. describes the physical models and assumptions implemented in the programs,
2. provides suggestions for modeling the MTF of objective lenses,
3. explains the interface to the detector data described in Chapter 12, and
4. suggests ways to use the programs to evaluate imager performance.
The programs are included for two reasons. First, the programs help the design engineer or systems analyst make imager design trades. The book provides suggestions for modeling optics and displays. The characteristics of available thermal FPAs are directly coupled to the Thermal computer program speed performance analysis. The computer programs are designed to provide quick but physically reasonable performance estimates.
The second reason for including the programs is to let the reader experiment with the theory. Blur, noise, and aliasing interact with target size and contrast to establish performance. For a given imager design, the relative importance of each factor is probably not obvious. For example, the dependency of aliasing on blur is clear from the theory. But the impact or importance of aliasing is not clear until the reader runs specific examples. The programs allow the user to vary imager and target characteristics while observing the effect on imager resolution.
Section 11.1 provides suggestions for estimating optical MTF. Section 11.2 provides estimates for the blur associated with the most common display technologies. Section 11.3 discusses the effect of atmosphere on performance and describes modeling assumptions. Thermal recalculates detectivity for each background temperature input by the user. The detectivity algorithms used in the program are summarized in Section 11.4. Both Thermal and Reflective models calculate diffusion MTF as well as spatial MTF for detectors. Detector MTF calculations are also described in Section 11.4. Section 11.5 explains computer program inputs and outputs. Section 11.6 offers suggestions for using the programs to analyze imager performance.