Figure 4.

Diffuse THz spectroscopy, (a-d) the bimodality spectra obtained using the diffuse extinction spectra and their MODWT detail vectors at the oblique detection angles including ${\theta }_1={18}^{\circ }$, ${\theta }_2={36}^{\circ }$, ${\theta }_3={72}^{\circ }$, and ${\theta }_4={90}^{\circ }$, (e-h) the ROC curves obtained for the identification of the region of $\alpha$-lactose using the diffuse extinction spectra and their MODWT detail vectors at each oblique detection angle, (i-l) similar to (e-h) for the identification of the region of PABA, (m-p) similar to (e-h) for the identification of the region of HDPE.