Orchard Water Stress Detection Using High-Resolution Imagery

This communication presents the Photochemical Reflectance Index as a pre-visual water stress indicator for olive and peach trees. Experiments were conducted on orchards located in southern Spain, where different deficit irrigation treatments were applied. The first field campaign was carried out in 2005 acquiring 2 m spatial-resolution imagery with the hyperspectral sensor AHS operated by the Spanish Aerospace Institute (INTA). The other campaigns happened in the summers of 2007 and 2008 when a thermal camera (Thermovision A40M; FLIR, USA) and a 6-band multispectral camera (MCA-6, Tetracam, Inc., California, USA) with a spatial resolution of 0.40 and 0.15 m respectively were used. Results show high correlation between PRI derived from high-resolution imagery and conventional water stress indicators measured in the field (i.e. stomatal conductance and stem water potential). For instance, a coefficient of determination of 0.8 was found for the relationship between crown PRI and temperature for peach trees, and for that between crown PRI and stem water potential in olive trees. We conclude that high-resolution multispectral imagery can be used for the remote detection of water stress via a physiological index, PRI, and that this technique is a viable option for irrigation scheduling of orchard crops.