an instrument for measuring the effective radiation of the earth’s surface, that is, the difference between the self-radiation of the earth’s surface and the atmospheric back radiation. During measurement of the effective radiation, the detecting surface of the pyrgeometer (see Figure 1) is turned alternately to the sky and the earth. The difference between the quantities obtained corresponds to the effective terrestrial radiation.

Figure 1. Detecting unit of a Savinov-lanishevskii pyrgeometer (external view)

The thermoelectric pyrgeometer of S. I. Savinov, as improved by lu. D. Ianishevskii, is used in the USSR. The detector consists of alternate coarse black strips and shiny nickel-plated strips. Because of the difference in the strips’ emissivity and absorptivity, a temperature difference is created. The thermoelectric current that arises is measured with a galvanometer. The instrument is calibrated in absolute values (caJories/cm²-min) by comparison with the readings of an Angstrom compensation pyrheliometer or by reference to black body radiation. V. A. Mikhel’son built an absolute compensation pyrgeometer with strips facing in opposite directions that permits a direct determination of the effective radiation of the earth’s surface.