Efficient full field of view polarimetric calibration method for simultaneous imaging polarimeter

The Off-axis Three-mirror Simultaneous Imaging Polarimeter (OTSIP) is a kind of polarimetric remote sensor with high spatial resolution. In OTSIP, simultaneous measurements were performed by means of prism dividing amplitude. Due to various equipped polarizers and complex polarimetric characteristics of OTSIP, its instrument matrix will deviate from the ideal value. In order to ensure the polarimetric accuracy of OTSIP, the development of an efficient polarimetric calibration is indispensable. In this paper, a calibration method using a standard linear polarization light source and circular polarization light source was proposed. The first three columns of the instrument matrix were firstly calibrated by a linear polarimetric calibration source to obtain the calibration coefficients via the least-squares fitting algorithm, and then the fourth column of the instrument matrix was calibrated by a circular polarimetric calibration source. Moreover, the nonideality of circular polarization state light was significantly improved by averaging measured results at 0 and 90° azimuths. As for the full field of view polarization calibration, a linear fitting method to each element of the instrument matrixes at multiple field of view angles was used. The resulting polarimetric measurement accuracy showed that the linear and circular polarization measurement accuracy was better than 1% (DOP<=0.3), validating the effectiveness and feasibility of this polarimetric calibration method. This method greatly improves the calibration efficiency of the OTSIP, making it possible to calibrate the polarimeter in flight.