Theoretical error analysis of photoelastic modulator based spectropolarimetric imager

Photoelastic-modulator(PEM) generating a beat signal that modulates the polarized component of the incident light is employed in spectropolarimetric imager. Multispectral and polarized information can be achieved in target detection. The measurement accuracy is a critical technical index. In order to research the elements affecting the measurement accuracy of the instrument, the theoretical measurement principle and the optical structure characteristics are introduced. The polarization radiation measurement model is established by using mathematical description called Stokes-Muller and pseudo-inverse matrix is used to realize demodulation of incident light. Sensitivity of Degree of Linear Polarization (DOLP) retrieval to errors in retardance amplitude, retardance amplitude mismatch resulted from incident angle, scene gradient and phase error and detector noise is analyzed when different polarized incident light is considered. The result shows that relative error of DOLP is less than 0.5% and retardance amplitude error affects DOLP most. The study provides a theoretical basis for development, calibration and data processing of the instrument.