A technique is developed for calibration of a lidar used to measure backscattering matrices (BSM). The technique exploits the fact that the well-known normalized molecular backscattering matrix is independent of the air density. An algorithm is described for separation of the aerosol component from BSM of an aerosol-gas mixture and estimation of errors in determination of BSM elements from a single measurement. The latter gives a criterion of quality of the obtained results to be used in the further BSM analysis.