Experimental study of brightness surface temperature angular variations ofmaritime pine (Pinus pinaster) stands

An experimental design based on an airborne TIR camera equipped with wide-a ngle lenses for measuring directional brightness temperature over forest ca nopies is described. A particular care is given to the analysis of possible sources of errors (related to instruments and atmosphere) and to their cor rections. The protocol of data acquisition is adapted to provide TIR measur ements in a -60 degrees-+60 degrees range of zenith view angles and in all azimuthal directions. The results obtained over maritime pine (Pinus pinast er) stands in the Landes forest in the southwest of France during summers 1 995 and 1996 reveal important hot spot effects and differences of brightnes s temperatures reaching 4 K between vertical and oblique measurements. Acqu isitions performed over stands of different ages, between 5 and 48 years ol d, also illustrate the dependence of the structure of stands on the hot spo t. (C)Elsevier Science Inc., 2000.