Satellite derived leaf area index derived from SOPT time series in the ADAM project

This study investigated the potential of high spatial resolution and high revisit frequency observations to monitor the LAI distribution over regional domains. It is based on the ADAM experiment during which 39 SOPT images were acquired from October 2000 and July 2001 over the study area located close to Bucharest in Romania. The study focuses on wheat crops for which intensive ground measurements were performed over the whole growing season for 40 elementary sampling units corresponding to about 30×30 m². The sampling units were divided into 10 for calibration and 30 for validation. The approach is based on the use of a semi-empirical model of LAI dynamics (MODLAI). It was first adjusted on the calibration units to smooth out local measurement uncertainties and interpolate the measurements to the dates of SPOT acquisition. Then empirical transfer functions were derived for each date, based on multiple linear regressions. Finally, the LAI was estimated for all the validation units at the SPOT dates. MODLAI was adjusted to the retrieved LAI of the validation units, and used to interpolate the values to the date of ground measurements. Finally, the LAI values derived this way were compared to those measured directly in the field. They show a very good consistency. The potentials of this approach and its adaptation to other applications are then discussed.