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Chapter 8: Sensors for Measuring the Polarized State of a Beam
We have throughout the earlier chapters made the assumption that we could observe and record the polarized state of the EM energy reaching a sensor. In this chapter we will present some of the basic methods for sensing polarized radiation. We begin with simple intuitive approaches (Sec. 8.1) and then introduce full Stokes vector sensors in Sec. 8.2. Section 8.3 extends the principles of the first two sections to imaging sensors, which are of the most interest for direct remote sensing applications. Finally in Sec. 8.4, we introduce some of the sensor-related issues associated with polarimetric imaging for remote sensing. Throughout this chapter we emphasize the general issues of sensing as they relate to understanding the nature of the remotely sensed signal. The details of sensors and sensor design are beyond the scope of this treatment, so for a more thorough treatment the reader should consult the references for this chapter and the current literature.
8.1 Sensing of Polarization Contrast
For cases where linear polarization dominates the polarized portion of a partially polarized beam, it is possible to use very simple methods to capture some of the polarimetric character of the signal. Consider the case shown in Fig. 8.1 (a) of partially polarized flux incident on an extremely simple sensor. The sensor is made up of a linear polarizer followed by an aperture that controls the field of view of a detector. A more efficient design is shown in Fig. 8.1 (b) where a lens is used to more effectively gather the flux and control the field of view. To deal rigorously with the design in Fig. 8.1 (b), we would need to introduce the polarimetric Mueller matrix of the optic, so we will continue with the simple design in Fig. 8.1 (a) for the present.
Assume that the linear polarizer is oriented with its transmissive axis along the horizontal axis.
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