infrared
adjective uk/ˌɪn.frəˈred/ us/ˌɪn.frəˈred/
红外线的
Infrared light is a type of light that feels warm but cannot be seen.
Their pilots are guided by an infrared optical system that shows images clearly even at night. 他们的飞行员使用红外光学系统导航，即便在夜晚也能清楚地显示影像。