Robust estimation of Stokes parameters with a partial liquid-crystal polarimeter under thermal drift.

Polarized light carries information about the various physical parameters that have been acting upon it. Obtaining information on the observed object by studying the polarization of light reflected can be accomplished by several methods. The four Stokes parameters of the reflected light wave (S0, S1, S2, and S3) are generally estimated by observing the scene, with a CCD sensor, through a polarimeter. This device relies on acquisition of multiple frames relative to an adjustment parameter of the optical components: positioning angle or optical delay. In real-time applications, the polarimeter often uses liquid-crystal components. The adjustment retardation parameter is then controlled by an electric voltage. However, the retardation introduced by a liquid-crystal variable retarder (LCVR) is strongly dependent on temperature. One solution is to hold constant the LCVR temperature by using a thermostated environment, but this is not always possible (power consumption in remote sensing, for instance). In J. Opt. A2, 216 (2000), Bueno has showed that, in this latter case, it is necessary to calibrate the LCVR just before carrying out measurement and to do this again approximately every 10 min. In this article, we propose a robust and accurate solution, based on the self-calibration principle, for measuring the Stokes parameters of partially linearly polarized light. Unlike methods generally reported in the literature, our polarization parameter estimation is independent of the accurate knowledge of the polarimeter variable retardation values and, thus, does not require a calibration process at regular intervals.