In order to visualise the seasonal changes in reflectance at the two sites, 3-D plots were constructed, with the X- 
axis representing wavelength, Y-axis percentage reflectance, and Z-axis time. Figure 1 shows the plot for the 
ash site and figure 2 that for the beech site. These plots proved to be a useful, highly visual way of showing 
clearly the contrasts in amplitude and timing of spectral reflectance variation between the two sites. The 
remainder of this paper will focus upon (i) seasonal trends in reflectance within visible and near infra-red 
wavelengths, both individually and when combined as a vegetation index and, (ii) seasonal variation in the 
wavelength position of the maximum slope within the region 680-750nm. 
Figure 1. Seasonal variation in spectral reflectance at the ash site. 
Figure 2 . Seasonal variation in spectral reflectance at the beech site. 
3.1 Seasonal variations in visible and near-infrared reflectance 
Seasonal variations in mean visible and near-infrared reflectance are shown in figure 3. For both sites visible 
reflectance varies between 1 and 6 % throughout the year, and the overall shape of the seasonal reflectance 
curves are similar for both species, however, the timing of some significant fluctuations differs. In terms of 
mean near-infrared reflectance, the ash canopy varies over a much more limited range (20 to 30%) than the 
beech (15 to 40%), with more gradual fluctuations. To account for the different seasonal variations in