Determining Biophysical Parameters for Olive Trees Using CASI-Airborne and Quickbird-Satellite Imagery

This study reports on the development of remote sensing methods for estimation of biophysical parameters in olive orchards. Field and airborne campaigns were conducted in 2003 and 2004 in two orchards located in southern Spain. Ground measurements of crown transmittance and leaf area index (LAI) of individual olive trees (Olea europaea L.) were done using the LAI-2000 Plant Canopy Analyzer. Hyperspectral images were acquired with a compact airborne spectrographic imager (CASI) at 1-m spatial and with QuickBird satellite sensor at 2.5-m spatial resolution. The panchromatic 0.6-m spatial resolution image was also acquired with QuickBird. These images enabled the application of automatic algorithms for olive crown identification and delineation, to determine tree crown size and LAI. These methods proved successful for determining projected olive crown area, obtaining determination coefficients (r ²) in the range of 0.82 to 0.65, and root mean square errors (RMSE) of 4.8 and 6.2 m² for CASI hyperspectral and QuickBird panchromatic images, respectively. The olive crown volume was estimated using image-estimated projected crown area values, yielding r ² ranging between 0.87 and 0.70, with RMSE of 8.4 and 11.3 m³ for CASI hyperspectral and QuickBird panchromatic images, respectively. Olive crown transmittance and LAI of individual olive trees were evaluated using spectral vegetation indices (normalized difference vegetation index [NDVI], renormalized difference vegetation index [RDVI], simple ratio index [SR], modified simple ratio [MSR]) yielding better correlations with CASI images, r ² in the range 0.71 to 0.75 (P < 0.0001) and 0.57 to 0.62 (P < 0.0001) for crown transmittance and LAI, respectively. These methods enable obtaining maps of biophysical parameters in olive trees at farm scale in an operational way demonstrating the validity of the methodology used.