Here is what Alan Siddons says as concerns backradiation and measuring DLR and DLR:
I believe that so-called back-radiation is simply the natural result of heating the atmosphere, whether by radiation or convection. A heated body will radiate, and its radiation will be observable from any point of view. A similar kind of thing happens in spectroscopy.
Against a bright source of illumination — like a satellite peering down at the radiating earth — a gas will be seen to absorb certain frequencies of light. Against a dark background, however — like an IR-detector on the surface pointed up toward space — the same gas will be seen to emit certain frequencies of light. But this certainly doesn’t mean that heat is being radiatively transferred to the illumination source, i.e., the surface.
Against a bright source of illumination — like a satellite peering down at the radiating earth — a gas will be seen to absorb certain frequencies of light. Against a dark background, however — like an IR-detector on the surface pointed up toward space — the same gas will be seen to emit certain frequencies of light. But this certainly doesn’t mean that heat is being radiatively transferred to the illumination source, i.e., the surface.
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Alan Siddons is right. It's basic thermodynamics.
SvaraRaderaBut in this comment, there is the possibility of confusion:
"But this certainly doesn’t mean that heat is being radiatively transferred to the illumination source, i.e., the surface."
If by this comment, we mean that a hotter surface does not have heat transferred from a colder atmosphere, then with the right understanding of "heat" we can all agree. (Net transfer between bodies).
If by this comment it means that radiation from the atmosphere has no effect on the surface then this would violate the first law of thermodynamics.
Take this radiation source away and the surface will get colder. Therefore - "an effect".
You are playing with words: A coat of course has "an effect" on the temperature of your skin, but not by "backconduction". Take the coat away
SvaraRaderaand you will freeze. Science is not about confusing playing with words.
It is about realities.
Evidently we agree on the realities: Net transfer from hot to cold.
SvaraRadera