How to April Fool Yourself

Today April 1st it is the right day to recall the post from 2011 How to Fool Yourself with a Pyrgeometer with related posts connecting to the recent sequence of posts on temperature vs radiation.

Thus you should go to a Clas Ohlson Store and buy yourself a pyrgeometer or infrared thermal camera and direct it to the atmosphere and read that the instrument on its display reports as Downwelling Longwave Radiation from the atmopsphere of about 330 Watts per square meter supposedly then hitting everything on the Earth surface, twice as much as the 170 W/m2 coming in as short wave radiation from the Sun.

Or direct the instrument to the ground and read that the Earth gives off 290 W/m2 as Upwelling Longwave Radiation, almost twice what comes in from the Sun.

What's going on? Have you been fooled by the instrument, or are you too smart for that understanding very well how a infrared thermal camera works? What does the instrument in fact directly measure? Temperature  or radiation?

Once you have figured that out, you can now go ahead to fool your neighbour.  

You may compare with a potentially equally shocking misreading of a thermometer mixing Celsius with Fahrenheit or even worse with Kelvin.