The volume depolarization ratio of the molecular backscatter signal detected with polarization lidar varies by a factor of nearly 4 depending on whether the rotational Raman bands are included in the detected signals of the individual system or not. If the rotational Raman spectrum is included partially in the signals, this calibration factor depends on the temperature of the atmosphere. This dependency is studied for different spectral widths of the receiving channels. In addition, the sensitivity to differences between the laser wavelength and the center wavelength of the receiver are discussed.