A method based on time-gated multiwavelength retroreflection is described to identify optical systems (OS) and discriminate false alarms. A test-bed consisting of a combination of a pulsed laser synchronized with a gated camera and a laser rangefinder was developed for detecting retro-reflection. The proposed method is based on the chromatic aberrations of the OSs of interest, which retro-reflect multiple interrogation wavelength signals. A calibration formula to evaluate the optical cross section from the system signature at the selected wavelengths is used for identification of and discrimination against false alarms.