Figure 3. The continuum removed reflectance (Figure 3a) of the 2.1 µm absorption feature for two dried and ground Douglas-fir samples: a low nitrogen sample (dashed line) and a high nitrogen sample (solid line). The ratio of these two continuum removed reflectance spectra are shown in Figure 3b indicating that absorptions at 2.054 µm and 2.172 µm cause a broadening of the 2.1 µm absorption feature as nitrogen concentration increases.