IR crossover refers to which condition?

• A. The time at dawn and dusk that the terrain and the target are close enough in temperature to blend in
• B. A moment when infrared sensors cross into a different wavelength band
• C. A measure of infrared sensor sensitivity
• D. The range at which IR detection begins

Answer: (A)

Thermal crossover is about when the heat differences between a target and its surroundings become minimal. At dawn or dusk, the terrain and the target can settle at similar temperatures, so the infrared signature blends in with the background. That moment of minimal contrast makes detection and tracking by IR sensors much harder, which is why crossover is defined as the time when terrain and target are close enough in temperature to blend in.

It isn’t about changing to a different wavelength, nor about how sensitive the sensor is, or the distance at which detection begins. Those ideas describe other aspects of infrared sensing, not the point at which thermal contrast disappears.