In infrared thermography, a thermal gradient is seen as what?

• A. A uniform temperature field
• B. A change in temperature over distance
• C. A color-only gradient with no temperature change
• D. A constant radiance

Answer: (B)

A thermal gradient is a change in temperature over distance. In infrared thermography, the camera detects infrared energy emitted by surfaces and translates it into temperature information. When temperatures vary across different parts of a scene, adjacent areas emit different amounts of infrared energy, so the image shows a progression of brightness or color that represents those temperature differences. If the temperature were the same everywhere, there would be no gradient and the image would appear uniform. Likewise, a color change without an actual temperature difference would not be a true gradient, and constant radiance implies no temperature variation. So the concept being tested is that a thermal gradient reflects how temperature changes as you move through space. For example, a hot object cooling along its length would produce a measurable change in temperature over distance, which is what the gradient captures.