The Development of Standard Instruments for Radiation Measurements

The development of instruments for the measurement of solar radiation fluxes is reviewed with emphasis on instruments that can be used as primary or secondary standards for meteorological radiation measurements. The fundamental principles used in radiometric instruments are briefly discussed. It is shown that calorimetric techniques are the best suited for precision measurements because of their fundamental independence of the spectral characteristic of the fluxes to be measured. A simple first-order model of the caloric radiometer is used to demonstrate its different useful modes of operation. The historical evolution is shown by a discussion of the famous classical instruments that in their modern versions still represent or support the International Pyrheliometric Scale. Areas of possible improvement of today’s instruments are indicated and two very recent attempts to construct radiometers of the highest precision are described.