Relations between Directional Spectral Vegetation Indices and Leaf Area and Absorbed Radiation in Alfalfa

摘要: Abstract Sensors on satellite platforms with extreme view angles have been increasingly used to analyze regional and global vegetation cover productivity because of frequent observations. This study, using experimental theoretical methods, analyzed variations in indices sun-view geometry as a means understanding the sensitivity relations beween biophysical properties, leaf area index (LAI), instantaneous fraction absorbed photosynthetically active radiation (fAPAR). Canopy bidirectional reflectance factors (BRFs) an alfalfa crop were measured simulated at variety solar zenith angles. Also, fAPAR, LAI, optical properties measured. Measured canopy reflectances agreed generally within 1% (absolute). Normalized difference simple ratio (NDVI SRVI, respectively), derived from BRFs, varied The minimum for near-infrared (NIR) BRFs relatively high red occurred near nadir, resulting some lowest values. Highest VI values obtained forward Variation NDVI sun-view-geometry was greatest LA's 2. indicate that between LAI SRVI fAPAR curvilinear across all angle combinations principal plane, whereas linear curvilinear. Analyses revealed large poorly correlated those small strongly correlated. In general, more sensitive than which is attributed fact quantity, nonlinearly related radiation. Regression NIR similar nonsimilar directions indicates highest correlation near-nadir backscatter directions. However, further investigation into remotely sensed observations attributes usefulness off-nadir extracting information recommended.