MONITORING SOIL MOISTURE DEFICIT EFFECTS ON VEGETATION PARAMETERS USING RADIATIVE TRANSFER MODELS INVERSION AND HYPERSPECTRAL MEASUREMENTS UNDER CONTROLLED CONDITIONS

摘要

Plant-available soil moisture is a key element which affects plant properties in their ecosystems. This study shows Poa pratensis -a species of grass- responses to soil moisture deficit during an artificial drought episode in a greenhouse experiment. We used radiative transfer model inversion to monitor the gradual manifestation of soil moisture deficit effects on vegetation in a laboratory setting. Plots of 21 cm x 14.5 cm surface area with Poa pratensis plants that formed a closed canopy were subjected to water stress for 40 days. In a regular weekly schedule, canopy reflectance was measured. The 1-D bidirectional canopy reflectance model SAIL, coupled with the leaf optical properties model PROSPECT, was inverted using hyperspectral measurements by means of an iterative optimization method to retrieve vegetation biophysical and biochemical parameters (mainly; LAI, Cab, Cw, Cdm and Cs). The relationships between these retrieved parameters with soil moisture content were established in two separated groups; stress and non-stressed. All parameters retrieved by model inversion using canopy spectral data showed good correlation with soil moisture content in the drought episode. These parameters co-varied with soil moisture content under the stress condition (Chl: R~2= 0.91, Cw: R~2= 0.97, Cs: R~2= 0.88 and LAI: R~2=0.48) at the canopy level.