No they don't assume that. They are measuring incoming infrared radiation.
Some are, some arent. I have been through all this with Trakar before, but since it is short, I will cover it with you again. First, lets look at the ones that don't.
An uncooled infrared radiometer pointed at the sky will measure the frequency of any incoming "light" and makes a calculation based on Wien's displacement law to determine the temperature of the "light" emitter or source of the radiation. Then using Stefan-Boltzmann's law Q = sigma T^4, suggests a downdwelling IR "flux" from the atmosphere.
Based on this, climate "scientists" claim to be able to prove the effects of "greenhouse" gasses. The question is, are they? I don't believe they are and here is why.
Do you think it is proper to use Stefan-Boltzman in the form of Q = sigma T^4 in an attempt to measure downdwelling IR from greenhouse gasses in the atmosphere? Stefan-Boltzman describes the radiant energy from a blackbody into a surrounding space at zero degrees Kelvin. The problem lies in the fact that the surface of the earth is not at zero degrees Kelvin and not only that, is warmer than the emitting source of the radiation.
Then there are the radiometers that actually do measure downdwelling radiation but each and every one of them proves that downdwelling radiation is not a source of IR to the earth.
The radiometers that can actually measure downdwelling radiation have, each and every one, been cooled to a temperature far below the -20C temperature of the atmosphere in order to make it possible to take a direct measurement. Just as predicted by the second law of thermodynamics.
For example:
Cryocooler Assembly
"Low vibration, long life focal plane operation near 58 K is critical to the success of AIRS.."
Dewar Assembly
"The focal plane assembly operates at 58 K for high sensitivity and is packaged in a permanent vacuum dewar which mates directly to the 155 K grating spectrometer."
58K = -215 deg C !!
Focal Plane Assembly
"The PV modules consist of 1, 2 or 4 bi-linear arrays of back-side-illuminated HgCdTe detectors"
"The AIRS FPA is unique in its hybrid PV/PC approach and required special care in the routing, shielding and grounding of very low noise (nV) PC signals in the presence of high level (V) PV signals. A total of 526 leads interconnect to the motherboard assembly using a series of 10 high-density, thin-film flex cables specifically designed for cryogenic operation
TES Instrument Specifications
"Individual detector array spectral coverage (cm-1) 1A (1900-3050), 1B (820-1150), 2A (1100-1950), 2B (650-900) All mercury cadmium telluride photo voltaic at 65 K "
65K = -208 deg C!
Each and every one of these instruments used to measure downdwelling radiation is cooled to a much lower temperature than the atmosphere so that the radiation will flow towards the instrument. Every measurement that claims to have measured downdwelling radiation has been either deliberatly, or through ignorance, falsified.
You only need look as far as the second law of thermodynamics to see the truth.
Second Law of Thermodynamics: It is not possible for heat to flow from a colder body to a warmer body without any work having been done to accomplish this flow. Energy will not flow spontaneously from a low temperature object to a higher temperature object.
If they did not cool the radiometers, they would get no measurement as the downdwelling radiation would not flow to the warmer earth just as the 2nd law states.
Man can do that. We have the tech to do it.
Man does not have the technology to violate the laws of physics. Th
It isn't an impossible measurement to make as you seem to think.
Then why do they have to cool the instruments to a temperature lower than the atmosphere in order to get a direct measurement?
Just as we can measure how much visible light is coming from a certain direction, so can we measure how much infrared light, or UV light or any other kind of light is coming from a certain direction.
Only if the insturument is cooler that the source because energy will not flow from cool to warm. If you don't cool the instrument, you get nothing but noise.
And when scientists point instruments up at the sky, they detect large amounts of infrared coming down, and it's source must be the atmosphere itself.
They only detect that radiation if they cool their instruments to a temperature lower than the atmosphere. If they don't cool the instruments, the radiation won't flow into the instrument. Cool will not move spontaneously to warm. The second law again.
I will have to get to the reset of your posts tomorrow.