[1] Univ Ouagadougou, Dept Phys, LPCE, Ouagadougou, Burkina Faso
[2] CIRAD, Unite Rech Biomasse Energie, F-34398 Montpellier, France
[3] Ctr Natl Rech Sci & Tech, IRSAT, Ouagadougou, Burkina Faso
[4] Univ Montpellier 2, Supagro Montpellier, CIRAD, INRA,UMR IATE 1208, F-34060 Montpellier, France