Measuring Downwelling Longwave Radiation DLR?

CO2 climate alarmism is based on the idea of "backradiation" with an atmosphere of "greenhouse gases" absorbing infrared radiation from the Earth surface and then "backradiating" part of it to the Earth surface in the form of Downwelling Longwave Radiation DLR with a warming effect. This is the 324 W/m2 in the lower right hand corner of the above figure.

In previous posts we have questioned the reality of this recirculation of radiation, based on

a theoretical mathematical/physical argument using Ockham's razor.

On the other hand, climate alarmists argue that DLR is real, because you can measure it.  

Both theory and observation require interpretation to connect to reality. We are thus led to check how measurements of DLR are done and interpreted.  

In Ten-year Global Distribution of Downwelling Longwave Radiation  we learn:

• The fluxes were computed using a deterministic model for atmospheric radiation transfer, 5 along with satellite and reanalysis data for the key atmospheric input parameters, i.e. cloud properties, and specific humidity and temperature profiles.
  

So DLR is computed from certain atmospheric input (cloud, humidity, temperature) using a certain model and out comes Downwelling Longwave Flux DLF of about 324 W/m2. Does it mean that the DLF is real? 

The above figure is presented by the Climate Monitoring SAF EUMETSAT Project offering the following "products":

• TIS Total Incoming Solar Radiation
• TRS Total Reflected Solar Radiation (shortwave outgoing)
• TET Total Emitted Radiation (longwave outgoing)

The figure also includes 324 W/m2 DLF but this is a not a "product". Why is then DLF not a 

product? Because it is not directly measured, only computed from a certain model?

The search for the true nature of DLF continues...real or fictional? 

One way to compute DLF is to integrate an emission spectrum.  The crucial issue is then if the emission spectra of two blackbodies independently determine a two-way radiative flux between the bodies, or if there is only a one-way radiative flux from warmer to cooler. What do you think? You probably know what I think: See e.g. the previous post Radiative Budget: In and Out.