SPECTRAL PROPERTIES OF LAND SURFACES IN THE THERMAL INFRARED .1. LABORATORY MEASUREMENTS OF ABSOLUTE SPECTRAL EMISSIVITY SIGNATURES

A laboratory procedure to obtain absolute spectral emissivity signatures of soils in the thermal infrared is developed and discussed. Particular attention is given to correction for environmental radiation and to the estimation of the final accuracy attainable. The study covers the (3.0-5.5) μm and the (8.0-13.5) μm bands with a spectral resolution of 2.5% of λ. The method does not require any a priori assumption on the physical parameters, nor does it require any direct temperature measurement. Absolute emissivity signature ελ can be measured within ± 0.6%. Bidirectional reflectivity signatures, ρbλ(0,0), are obtained as well, against a reflectivity standard: a flame-sprayed aluminum diffusor. -from Authors