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.
Most rocks, minerals, and sands show strong infrared reflection bands. In the atmospheric window (8 to 12micro), quartz and feldspar show an emissivity near 0.8, calcite near 1.0. These laboratory data are confirmed from observations during a Tiros flight over the Libyan desert. The Mediterranean Sea was used for calibration. Desert emissivity is between 0.7 and 0.9.
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