The determination of infrared emissivities of terrestrial surfaces

Infrared signals received in the 8- to 12-μ window by weather satellites and aircraft are dependent on surface temperature (Ts), surface emissivity (ε), and atmospheric interference. It seems that nowhere can variations of ε be neglected in order to evaluate Ts data correctly. Methods of determining ε of typical surface materials are presented. They are: (1) determinations from reflection data obtained from polished rock samples run on a spectrophotometer; (2) a fieldworthy device constructed by the authors, called the emissivity box; and (3) ε as inferred from Tiros data. Over the Sahara, emissivity of SiO2-containing surfaces is frequently below 0.95. Emissivity of water and oil on water are shown to differ.