Angular variation of thermal infrared emissivity for some natural surfacesfrom experimental measurements

Multiangle algorithms for estimating sea and land surface temperature with Along-Track Scanning Radiometer data require a precise knowledge of the ang ular variation of surface emissivity in the thermal infrared. Currently, fe w measurements of this variation exist. Here an experimental investigation of the angular variation of the infrared emissivity in the thermal infrared (8-14-mu m) band of some representative samples was made at angles of 0 de grees-65 degrees (at 5 degrees increments) to the surface normal. The resul ts show a decrease of the emissivity with increasing viewing angle, with wa ter showing the highest angular dependence (similar to 7% from 0 degrees to 65 degrees views). Clay, sand, slime, and gravel show variations of approx imately 1-3% for the same range of views, whereas a homogeneous grass cover does not show angular dependence. Finally, we include an evaluation of the impact that these data can produce on the algorithms for determining land and sea surface temperature from double-angle views. (C) 1999 Optical Socie ty of America.