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I started reading about passive sensors and radiometers in particular. I know that microwave radiometers work day and night and in cloudy conditions. Thermal radiometers can measure energy during the night also, which makes sense since the heat is radiated from the Earth at night.

My question is whether near-infrared energy can be captured at night by radiometers from space or onboard an aircraft, on the contrary of visible passive sensors obviously?

Hakim
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    According to https://en.wikipedia.org/wiki/Infrared a body would need to be at least 2000K to emit near infrared light, not even lava flows are that hot. according to https://en.wikipedia.org/wiki/Lava flows are at most 1200 C (1473.15 K). Infra red photography at night would have to be with a far infra red camera as near infra red would be totally black (in theory). – Michael Stimson Dec 12 '18 at 01:02
  • Thanks a lot, your comment seems to answer my question. Could you add it below, so I can accept it? – Hakim Dec 12 '18 at 13:36

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According to Wikipedia an object would need to be at a temperature of at least 2000K (Kelvin) to emit light in the near infra-red spectrum, not even lava flows are that hot according to Wikipedia lava flows are at most 1200C (Celsius, which when converted to 1473.15 Kelvin).

In order to see objects, like with a thermal camera, at night you would need to be photographing in the far infra-red spectrum as, in theory, a near infra-red image would be totally black.

Caveat: this is theoretic only, I have no experience with photographing in the infra-red spectrum to base a practical conclusion on.

Michael Stimson
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