Recent improvements in sensing technology have driven new research areas within the terahertz (THz) portion
of the electromagnetic (EM) spectrum. While there are several promising THz applications, several outstanding
technical challenges need to be addressed before robust systems can be deployed. A particularly compelling
application is the potential use of THz reflection spectroscopy for stand-off detection of drugs and explosives. A
primary challenge for this application is to have sufficient signal-to-noise ratio (SNR) to allow spectroscopic identification
of the target material, and surface roughness can have an impact on identification. However, scattering
from a rough surface may be observed at all angles, suggesting diffuse returns can be used in robust imaging of
non-cooperative targets. Furthermore, the scattering physics can also distort the reflection spectra, complicating
classification algorithms. In this work, rough surface scattering effects were first isolated by measuring diffuse
scattering for gold-coated sandpaper of varying roughness. Secondly, we measured scattering returns from a
rough sample with a spectral signature, namely α-lactose monohydrate mixed with Teflon and pressed with
sandpaper to introduce controlled roughness. For both the specular and diffuse reflection measurements, the
application of traditional spectroscopy techniques provided the ability to resolve the 0.54 THz absorption peak.
These results are compared with results from a smooth surface. Implications of the results on the ability to detect
explosives with THz reflection spectroscopy are presented and discussed. In addition, the Small Perturbation
Method (SPM) is employed to predict backscatter from lactose with a small amount of roughness.