Experimental investigation of the angular variation of emissivity in the thermal infrared band

Abstract

Multi-angle algorithms for estimating sea and land surface temperature with ATSR data require a precise knowledge of the angular variation of surface emissivity in the thermal infrared. Nowadays, very few measurements do exist of this variation. In this work an experimental investigation of the angular variation of the infrared emissivity in the thermal infrared (8 - 14 micrometer) band of some representative samples has been made at angles of 0 degrees - 65 degrees (at 5 degree increments) to the surface normal. The results show a decrease of the emissivity with increasing viewing angles, being water the substance with highest angular dependence (about 7% from 0 degree to 65 degree views). Clay, sand, slimy and gravel show variations about 1 - 3% in the same range of views while an homogeneous grass cover does not show angular dependence. Finally, we include an evaluation of the impact that these data can produce in the algorithms for determining land and sea surface temperature from double angle views.