What is the Purpose of Measuring DLR?

          Many pyrgeometers measuring net balance, while reporting gross input as DLR. Why?

When you in science measure something using some instrument, there must be a purpose of making the measurement. You would not buy an expensive instrument without purpose and without users, scientists would find no motivation for designing and constructing the instrument, and manufacturers would not find any incentive to produce without any demand.

Let us see what purpose we find in a typical publication of calibration of pyrgeometers designed for measuring downwelling longwave radiance DLR from the atmosphere to the Earth surface:

• Accurate measurements of the broadband longwave irradiance at wavelengths between 3.5 and50 microns are important for understanding the total energy balance at the earth’s surface. 
• Atmospheric Radiation Measurement (ARM) Program has acquired more than 100 pyrgeometers, a type of radiometer used for these measurements, for deployment in the Solar and Infrared Stations, SKYRAD, GNDRAD, and METRAD platforms at the Southern Great Plains (SGP), Tropical Western Pacific, ARM Mobile Facility installations, and the Unmanned Aerospace Vehicle program. 
• Proper calibration of these pyrgeometers is essential for producing accurate measurements of downwelling and upwelling longwave irradiance consistent with ARM research goals. 
Between 2002 and 2004, all SKYRAD, GNDRAD, Solar and Infrared Stations, and BRS pyrgeometers were calibrated using the then newly-developed National Renewable Energy Laboratory (NREL) Pyrgeometer Blackbody Calibration System.
• Recent results of data analyses by the Broadband Heating Rate Profile, including the Longwave Quality Measurement Experiment comparisons involving the Atmospheric Emitted Radiation Interferometer (AERI), indicated a significant and consistent pyrgeometer measurement bias of about -12 Wm-2 ± 5 Wm-2 under clear-sky conditions. 
• By March 2006, the resulting BCR-01162, Remove Pyrgeometer Calibration Bias, returned all pyrgeometer calibration values for field measurements to the original EPLAB thermopile sensitivities and dome correction factors set to 4.0 as originally deployed until the pyrgeometer calibration issues could be resolved. 

OK, we read that DLR is important for understanding the total energy balance of the Earth's surface, and that DLR is not easy to measure because elaborate calibration is needed to reach even very modest accuracy.

But if you are interested in the energy balance of the Earth's surface, you know that shortwave energy E_in from the Sun is absorbed and that the surface radiates longwave energy E_out to the (normally) colder atmosphere and to outer space. The energy balance is expressed as B= E_in - E_out as a net difference between E_in and E_out, and it is of obvious interest to seek to measure E_in and E_out to understand the energy balance.

But it would be meaningless to introduce a fictional quantity DLR which would be added and subtracted to the balance

• B = E_in + DLR - E_out - DLR = (E_in +DLR) - (E_out + DLR) ,

which you would seek to measure with some elaborate equipment to understand B. It would be meaningless since

• B = E_in - E_out, 

and that is all there is to say about the balance, and that can be measured. Adding and subtracting DLR and measuring DLR would be meaningless for you as a scientist and the operation of adding and subtracting DLR would have no physical correspondence; (E_in and DLR) and (E_out + DLR) would lack physical meaning.

How can you then understand that there is a whole industry of instrument manufactures and scientists who get together to measure DLR? It is clear that the need of measuring DLR comes from the scientists as the customers.

Why are then climate scientists interested in documenting E_in + DLR by measuring DLR? Because these climate scientists are alarmists and they seek signs of alarm. Suppose now with a proper design of the pyrgeometer it turns out that (E_in + DLR) can be made much bigger than E_in, say with a factor 3, so that

• (E_in + DLR) = 3 x E_in 

which would correspond to realistic data with E_in = 150 W/m2 and DLR = 300 W/m2. The energy balance would then be inflated by a factor 3. A perturbation to the net balance would then be magnified with a factor of 3, which could mean a change from harmless global warming of 1 C to alarming 3 C.

The trick of inflating the net energy balance by introducing the fictional quantity DLR, is cheap but has big scope. The fact that it was not directly decoded when it appeared as climate alarmism developed into our time, can only be explained by a mass exodus of scientists from rationality.

In business, it is illegal to artificially inflate the incoming money by creating invoices without reality behind which are balanced by invisible bills.

Is it OK in science? Who carries the responsibility? Is it Kipp&Zonen selling pyrgeometers reporting DLR? Is it the World Meteorological Organization asking for such instruments by refereeing to some old formula written by a now dead scientist supposedly setting a standard?

I have the itching feeling that I have met this before in academics. Something is seriously wrong, but no one is responsible. All physicists and mathematicians are on permanent vacation from reality.

Here is the energy balance of the Earth according to NASA: Yellow = E_in, Red = E_out without any DLR:

NASA would see no reason to buy any instrument for measuring DLR.  Why is ARM wasting tax money for this purpose?

Here is the purpose indicated in red supposedly showing the warming effect of CO2 in a DLR spectrum delivered by AERI: 

• The atmospheric emitted radiance interferometer (AERI) measures the absolute infrared spectral radiance (watts per square meter per steradian per wavenumber) of the sky directly above the instrument.

When faced with this spectrum how could you ever question that the trace gas CO2 changes the energy balance of the Earth? Isn't the parts marked in red undeniable evidence? No, it is not. It is fiction. If you have followed this thread then you understand that the spectrum is constructed from temperature, measured by AERI as an infrared thermometer. The spectrum is a deliberate fake construction intended for the purpose of selling CO2 alarmism. ARM is selling the story of DLR, while NASA does not even know that it exists.