Diner David J, Davis Ab, Hancock Bruce, Gutt Gary, Chipman Russell A, Cairns Brian
Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA.
Appl Opt. 2007 Dec 10;46(35):8428-45. doi: 10.1364/ao.46.008428.
A dual-photoelastic-modulator- (PEM-) based spectropolarimetric camera concept is presented as an approach for global aerosol monitoring from space. The most challenging performance objective is to measure degree of linear polarization (DOLP) with an uncertainty of less than 0.5% in multiple spectral bands, at moderately high spatial resolution, over a wide field of view, and for the duration of a multiyear mission. To achieve this, the tandem PEMs are operated as an electro-optic circular retardance modulator within a high-performance reflective imaging system. Operating the PEMs at slightly different resonant frequencies generates a beat signal that modulates the polarized component of the incident light at a much lower heterodyne frequency. The Stokes parameter ratio q = Q/I is obtained from measurements acquired from each pixel during a single frame, providing insensitivity to pixel responsivity drift and minimizing polarization artifacts that conventionally arise when this quantity is derived from differences in the signals from separate detectors. Similarly, u = U/I is obtained from a different pixel; q and u are then combined to form the DOLP. A detailed accuracy and tolerance analysis for this polarimeter is presented.
提出了一种基于双光弹调制器（PEM）的光谱偏振相机概念，作为一种从太空进行全球气溶胶监测的方法。最具挑战性的性能目标是在多个光谱波段中，以中等高空间分辨率、宽视场以及多年任务持续时间内，测量线性偏振度（DOLP），其不确定度小于0.5%。为实现这一目标，串联的PEM在高性能反射成像系统中作为电光圆延迟调制器运行。以略有不同的谐振频率操作PEM会产生一个拍频信号，该信号以低得多的外差频率调制入射光的偏振分量。斯托克斯参数比q = Q/I是从单帧期间每个像素获取的测量值中获得的，从而对像素响应率漂移不敏感，并最大限度地减少了传统上从单独探测器的信号差异中导出该量时出现的偏振伪像。类似地，u = U/I是从不同像素获得的；然后将q和u组合以形成DOLP。给出了该偏振计的详细精度和公差分析。
