Fig. 13.

Application of the temporal trend method developed with synthetic data to real observations. Plots show for all trees assessed in the field for defoliation and discoloration the rate of change between two consecutive hyperspectral flights (acquired one year apart: January and December 2015), in terms of PRI (a), TCARI/OSAVI (b), Macc (c), and CI (d), vs. NDVI. The bottom right panel shows the regression lines fitted to the most and least healthy trees (DEFO = 0 and DEFO = 5, respectively), illustrating how the slope between the rates of change for the CI vs. the NDVI decreased as tree health declined. Level 0 corresponds to trees without any sign of declining health, while other scores reflect the percentage of the crown displaying poor health: level 1 = [1–25%], level 2 = [26–50%], level 3 = [51–75%], level 4 = [76–99%], level 5 = 100%.