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Introduction to Thermal Testing

Introduction

History

Scientific Principles

Equipment - Detectors

Equipment - Imaging

Image Interpretation

Techniques and Applications

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Image Interpretation

Most thermal imagers produce a video output in which white indicates areas of maximum radiated energy and black indicates areas of lower radiation. The gray scale image contains the maximum amount of information. However, in order to ease general interpretation and facilitate subsequent presentation, the thermal image can be artificially colorized. This is achieved by allocating desired colors to blocks of grey levels to produce the familiar colorized images. This enables easier image interpretation to the untrained observer. Additionally, by choosing the correct colorization palette the image may be enhanced to show particular energy levels in detail.

Many thermal imaging applications are qualitative in nature. The inspection simply involves comparing the temperatures at various locations within the field of view. The effects of the sun, shadows, moisture and subsurface detail must all be taken into account when interpreting the image, but this type of inspection is straightforward. However, great care must be exercised when using an infrared imager to make quantitative temperature measurements. As mentioned previously, the amount of infrared radiation emitted from a surface depends partly upon the emissivity of that surface. Accurate assessment of surface emissivity is required to acquire meaningful quantitative results.