We demonstrate a prototype sensor capable of measuring specular and diffuse reflectance spectra from samples 3.6 m away. The sensor utilizes mid-wave to long-wave infrared supercontinuum light coupled into a rotational FTIR spectrometer to actively probe remote samples. We measure the diffuse reflectance of acetaminophen at 41.77 μg/cm² on a glass substrate and find that a modified Bobbert-Vlieger analysis can estimate the effects of particle size distribution on return spectra. We find that the measured return from stand-off particulate measurements depends not only on the chemical identity, but also the size and distribution of particles on the substrate.