chapter 9, Thermal Imager Topics

In Part II Evaluating the Performance of Electro-Optical Imagers from: Analysis and Evaluation of Sampled Imaging Systems

Author(s): Richard H. Vollmerhausen, Donald A. Reago, Jr., Ronald G. Driggers

Published: 08 March 2010

Chapter DOI: http://dx.doi.org/10.1117/3.853462.ch9

Chapter Page Count: 28 pages

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Frontmatter

Part I Analysis of Sampled Imaging Systems
1. The Sampling Process

2. Fourier Integral Representation of an Optical Image

3. Sampled Imager Response Function

4. Sampled Imager Optimization

5. Interlace and Dither

Part II Evaluating the Performance of Electro-Optical Imagers
6. Quantifying Visual Task Performance

7. Evaluating Imager Resolution

8. Quantifying the Effect of Aliasing on Visual Task Performance

9. Thermal Imager Topics

10. Imagers of Reflected Light

Part III Applications
11. Computer Programs and Application Data

12. Infrared Focal Plane Arrays

13. Appendix

14. Backmatter

15. Supplemental Programs: Thermal and Reflective

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Chapter Contents

9.1 Effective Blackbody Temperature
9.2 Signal and Noise in the Detectivity Model
9.3 Thermal Imager Contrast Threshold Function
9.4 Adding Aliasing Noise
9.5 Predicting Range Performance
9.6 Modeling Contrast Enhancement and Boost
9.7 Minimum Resolvable Temperature
9.7.1 Predicting minimum resolvable temperature
9.7.2 Predicting sampled imager minimum resolvable temperature
9.7.3 Improving the minimum resolvable temperature procedure
Bibliography

Excerpt

This chapter provides details on calculating signal and noise in thermal imagers. A detectivity model is used to calculate thermal imager contrast threshold function (CTF_sys). CTF_sys is used in the targeting task performance (TTP) metric to calculate imager resolution.

Thermal imagers sense heat energy with wavelengths between 3 and 12 μm. The 3- to 5-μm band is called midwave infrared (MWIR), and the 8- to 12-μm band is called longwave infrared (LWIR). Figure 9.1 shows typical atmospheric transmission for a 1-km horizontal path. There are three transmission windows from 3 to 4.2 μm, 4.4 to 5 μm, and 8 to 13 μm.

Everything near room temperature radiates in the infrared. The emissivity of natural objects is generally above 70%. Most manmade objects are also highly emissive. Thermal sensors derive their images from small variations in temperature and emissivity within the scene. Typically, the thermal scene is very low contrast.

Figure 9.2 shows the spectral radiant exitance from blackbodies at 300 K and 303 K. The difference between the two curves is also shown. The difference is small; however, a 3-K contrast represents good thermal imaging conditions.

http://dx.doi.org/10.1117/3.853462.ch9

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