ROSI performs specular and bidirectional reflectance measurements of spectrally neutral, non-fluorescent specular and diffuse samples at room temperature. It serves as the national reference instrument for specular and bidirectional reflectance measurements. The national reference instrument for directional-hemispherical reflectance measurements is the Spectral tri-function automated reference reflectometer (STARR).
ROSI uses a quasi-monochromatic system for illumination of the sample and broadband detection for the reflected radiation. Sample angles and positioning are controlled by a robotic-arm-based goniometer. Specular and bidirectional calibrations are collected in-plane, meaning the sample normal, illumination axis, and receiver axis are in the same plane. ROSI can also perform out-of-plane bidirectional reflectance measurements for research and special tests.