A calibration system is integrally provided with a polarimeter in which the calibration system and the polarimeter each receives a radiance sample from a spectral band of a scene. Radiances provided by the calibration system used to provide the relative responsivity calibrations among the polarimeter channels are essentially depolarized so as to provide the measurement data required to update the relative responsivity factors for the polarimeter channels. The unpolarized radiances from the calibrator are interspersed with scene data collected directly by the polarimeter, so that the polarimeter can effectively be recalibrated for each set of scene data obtained by the polarimeter. Such tracking of the calibration data can be studied for trends to assess instrument stability and to assess the appropriate means to preserve the measurement accuracy over periods where such changes occur. Another part of the calibration system may be used to adjust the scaling of the polarization calculated from the scene data obtained by the polarimeter. This is achieved by providing radiances which are essentially 100% polarized. An adjustment to the polarization magnitude scaling is performed if the "scene data" obtained by the polarimeter for the 100% polarized signal does not recognize the signal to be at 100% polarization.