Fluorescence, PRI and canopy temperature for water stress detection in cereal crops.

Narrow-band multispectral remote sensing techniques and thermal imagery were investigated for water stress detection in cereal crops. Visible and near infrared AISA eagle (Specim, Finland) and thermal AHS-160 (Sensytech Inc., USA) imagery were acquired on farm-level experimental site where maize and sorghum were grown with three different irrigation treatments. Vegetation biophysical and eco-physiological measurements were collected concurrently with the airborne campaign. As a measure of severity of water stress, field measurements of leaf photosynthetic efficiency (ΔF/F'm ), were compared against: i) the photochemical reflectance index (PRI), ii) the sun-induced chlorophyll fluorescence at 760 nm (F760), retrieved by the Frahunofer Line Depth method and iii) the canopy temperature (TC) calculated decoupling soil and vegetation contributions. TC was related to water stress with the highest determination coefficient (R2=0.65), followed by PRI586 (reference band at 586 nm) (R2=0.51). The relationship with F760 was significant but weaker (R2=0.36). Coefficient of determination increased up to 0.54 when pigment concentration was considered by multiplying ΔF/F'm and chlorophyll content, confirming the close relationship between passive fluorescence signal, pigment content and light photosystem efficiency. PRI586, F760 and TC maps were produced in maize and sorghum plots. Water treatments were well discriminated in maize plots by the three water stress indicators, although F760 patterns showed a higher degree of heterogeneity within plots. Among the indicators TC was less affected by canopy architecture since the unmixing techniques allowed to decouple the soil from the vegetation contribution. In sorghum plots water treatments were better discriminated by F760 and TC, probably due to saturation of PRI586 signal in sorghum canopy characterized by high LAI values.

JRC.H.3 - Forest Resources and Climate