At least one second beam of light from a first beam of light generated by a laser is directed into an atmosphere. Light therefrom scattered by molecules or aerosols in the atmosphere is collected by at least one telescope as at least one light signal, which together with a reference beam from the first beam of light are simultaneously processed by a Fabry-Perot etalon, and resulting fringe patterns are imaged onto a detector adapted to output a resulting at least one signal responsive thereto.