Discussion with Will Happer on Temperature vs Radiation Measurement

The discussion with Will Happer recorded in the previous post concerns the question what pyrgeometers and bolometers primarily measure: (a) temperature or (b) radiative heat energy flux. Will says (b) and I say (a). 

My argument is that if you look into the design of pyrgeometer, you see that it uses a thermopile, which is a device which reports a voltage which scales with the temperature difference between the two ends of the thermopile with one end by radiative equilibrium taking the same temperature as a distant source and the other end in contact with an ordinary thermometer which can be read. After calibration you can then from measured voltage and temperature read determine the temperature of the distant source. A pyrgeometer thus acts a thermometer which can read temperature at distance. This is what an infrared camera does.

A bolometer works in a similar way using a sensor with resistance scaling with temperature difference vs a thermal reservoir at constant known temperature.   

Will has another conception of pyrgeometers and bolometers:

1. Spectral intensity measurements are often expressed as equivalent temperatures. 
2. But the basic measurement is of energy fluxes which produce voltages or currents in sensor elements.

Will thus claims that the basic measurement is radiative energy flux and not temperatures. How can this be? 

Here 1 gives a clue: Will says that in some sense temperature and radiative energy flux are "equivalent". But what is this equivalence? After all, temperature is a state variable depending on the state of a system while radiative energy flux is a process variable depending on the process involved. In any case the standard procedure is to connect radiative flux $Q$ to temperature $T$ by the Planck/Stefan/Boltzmann Law for black/grey body radiation

• $Q=\epsilon\sigma T^4$      (1) 

where $\sigma$ is the Stefan-Boltzmann constant $\epsilon$ emissivity. This gives radiative flux the quality of a state variable, but this runs the risk to be misleading, since the process aspect is forgotten. A correct process version of the PSB Law reads

• $Q=\epsilon\sigma (T^4 - T_b^4)$   (2)

where $T_b$ is a background temperature like the temperature of the thermal reservoir for the bolometer. Only if $T_b=0$ does (1) give a correct connection between temperature and radiative energy flux and in addition the emissivity enters as an unknown to determine. Compare with next post.

The confusion increases by letting the pyrgeometer on its display show Downward Long Wave Radiation which is computed from the measured voltage as shown in PS3 below using (1) to express Outgoing Long Wave radiation from the instrument. A pyrgeometer thus measures temperature but reports radiative energy flux by using (1), which does not involve the process. You can thus be fooled by a pyrgeometer, which may be hard to accept if you just have bought one.   

My conclusion: 

• Pyrgeometers and bolometers do what is physically possible, namely to directly measure the temperature of a source by putting a thermometer in close or distant radiative contact with the source. 
• On the other hand, to measure radiative energy flux is very difficult since a whole process is involved with many unknowns and that is not what pyrgeometers and bolometers can do.
• See presentation at Climate Sense 2018. 

I am waiting for Will's conclusion.

PS1 Read about the Kipp and Zonen CGR3 Pyrgeometer:

• The CGR3 is a pyrgeometer, designed for meteorological measurements of downward atmospheric long wave radiation. 
• The CGR3 provides a voltage that is proportional to the net radiation in the far infrared (FIR). 
• By calculation, downward atmospheric long wave radiation is derived.

It is clearly stated that the pyrgeometer is a ghost detector serving climate alarmism measuring one thing (net temperature difference) and reporting something else (gross downward atmospheric long wave radiation), which is derived by (1). This has become so accepted, that even many skeptics believe in what the instrument display shows, although it defies scientific sense. If you have invested in a Kipp and Zonen CGR3 Pyrgeometer, you may not want to hear that you have bought a ghost detector, unless you want to send a ghost CO2 alarm…

PS2 You may compare measuring the difference between your body temperature and the surrounding room temperature, which is easy to do, with measuring how much your body is radiatively heated by the colder walls of the room, which is impossible without a ghost detector.

PS3 From the Kipp and Zonen Instruction Manual:

We see that the instrument display does not show net recording as the voltage $U_{emf}$ but instead gross $L_d$ as DWLR being computed from Formula 1 with $5.67*10^{-8}*T_b^4=\sigma T_b^4$ the incorrect gross outgoing upwelling ghost radiation from the pyrgeometer as if it was in radiative contact with outer space at 0 Kelvin. By claiming gross upwelling radiation, gross downwelling radiation is concluded, but the upwelling radiation is not real but ghost radiation. 

To well understand (not get fooled by) what an instrument display reports, it is necessary to look into the design of the instrument by reading the manual to see what is effectively measured and what is displayed. This is what I did above.