Potentiality of optical and radar satellite data at high spatio-temporal resolutions for the monitoring of irrigated wheat crops in Morocco

The potential of FORMOSAT-2 and ENVISAT/ASAR for the monitoring of irrigated wheat crops over Tensift/Marrakech semi-arid plain in Morocco is investigated. The green leaf area index (GLAI) was obtained from time series of vegetation index acquired by the FORMOSAT-2 instrument with a 25% accuracy. This information was then incorporated into a canopy functioning model to provide spatial estimates of GLAI, aerial biomass and top-soil moisture. These outputs were evaluated by comparing them to ground data collected on eight wheat fields monitored during the 2005–2006 agricultural season. The model accurately simulates the time courses of GLAI and aerial biomass during the vegetative phase. Finally, we analysed the spatio-temporal variations of ASAR backscattering co-polarization ratio (σHH/VV0) as a function of biomass water content on the basis of simulations performed over 69 other wheat fields. The purpose of such analysis is to retrieve this last biophysical variable from ASAR images. The sensitivity of ASAR data to vegetation appears to be deteriorated by the sensitivity of σHH/VV0 to the variability of soil conditions encountered in the study area (roughness and moisture).