In this study, a multispectral optical cavity (405, 450, 520 nm) allowing the measurement of extinction and scattering at 90° is developed. This cavity is intended to be miniaturized and eventually mounted on a UAV for temporally and spatially resolved measurements to study smoke plumes or for air quality monitoring. One of the first steps in this development, which is the subject of this study, is the design and commissioning of the cavity and its calibration. Indeed, the determination of the reflection coefficients of the mirrors constituting the cavity and the calibration of the sensors are a crucial step for the quality of the measurements. For this purpose, we used the generation of a "standard" aerosol (miniCAST) in the laboratory coupled with the Rayleigh Debye Gans for Fractal Aggregates (RDG-FA) theory. In the future, this cavity will provide information on the soot volume fraction, size and optical properties through the spectral dependence of the optical index.