Polarization measurements using a commercial off-the-shelf digital camera

Abstract

This paper presents a methodology to obtain polarization profiles using a commercial off-the-shelf (COTS) digital camera. It contains calibration techniques to ensure robust and accurate determination of the Stokes parameters and the system polarization state. It calculates the Stokes parameters for each scene pixel along with the degree of polarization, azimuth, and ellipticity angles for each of the RGB channels. A detailed calculation shows that the quasimonochromatic approximation for the wavelength dependence of the quarterwave plate can be extended to include the broadband RGB channels. A simple and inexpensive camera calibration converts RGB values to optical density and then to relative intensity values. An analysis is presented for the wavelength-dependent response of the tuned zero-order quartz quarterwave retarder, the broadband RGB channels, and the fourth Stokes parameter. The noise characteristics of the digital camera are analyzed along with a detailed calibration of the imagery for target characterization applications. An extensive validation process, using white light, compares calculated theoretical results with the empirical results from the COTS camera. A RGB pseudocoloring scheme, related to the Poincaré sphere, is introduced for the visualization of polarization parameters of daylight scenes.

Design for measurement of the polarization state of light based on division of wave front

“…It is especially suitable to the circumstances that the light is very dim and quickly changed. The method of the measurement described in this paper can be realized under the present scientific techniques and experimental conditions [5] . The system enables us to realize the real time measurement for light in practice.…”

“…There are a few methods to describe the polarization state of light [2] , whereas the method of the Stokes vector is the convenient one. Azzam, Matchko, and others [3][4][5] introduced many photoelectric detectors that are employed to measure the Stokes vector of light, and Tyo, et al [6] reviewed passive imaging polarimetry for remote sensing applications. There are mainly two kinds of methods [7,8] to measure the polarization state of light: light modulation method, and division-of-wave method.…”

Polarization azimuth angle in daylight scenes

“…16 A modern version of Lord Rayleigh's theoretical description for skylight polarization 3 is given by Figure 2 shows the scattering angle ⍀ in the observation plane containing the incident solar ray, scattering center, and observer. 17 Lord Rayleigh assumed the incident, unpolarized light is scattered by small isotropic particles ͑e.g., air molecules much smaller than the wavelength of light͒.…”

“…In previous work, 16,22 we described how the Stokes parameters can easily be encoded in a daylight scene. We assign RGB pixel values to the normalized values of S 1 , S 2 , and S 3 at each pixel site in the scene as follows:…”

“…8 were acquired using an Epson 850Z digital camera. In previous work 16 we described a methodology to obtain the four Stokes parameters for each scene pixel using a COTS digital camera. In this paper we present some applications of these tools and techniques to the analysis of the polarization azimuth angle ͑͒ for daylight-illuminated scenes.…”