First results from a dual photoelastic-modulator-based polarimetric camera

Abstract

We report on the construction and calibration of a dual photoelastic-modulator (PEM)-based polarimetric camera operating at 660?nm. This camera is our first prototype for a multispectral system being developed for airborne and spaceborne remote sensing of atmospheric aerosols. The camera includes a dual-PEM assembly integrated into a three-element, low-polarization reflective telescope and provides both intensity and polarization imaging. A miniaturized focal-plane assembly consisting of spectral filters and patterned wire-grid polarizers provides wavelength and polarimetric selection. A custom push-broom detector array with specialized signal acquisition, readout, and processing electronics captures the radiometric and polarimetric information. Focal-plane polarizers at orientations of 0 degrees and -45 degrees yield the normalized Stokes parameters q=Q/I and u=U/I respectively, which are then coregistered to obtain degree of linear polarization (DOLP) and angle of linear polarization. Laboratory test data, calibration results, and outdoor imagery acquired with the camera are presented. The results show that, over a wide range of DOLP, our challenging objective of uncertainty within +/-0.005 has been achieved.

Exploration of a Polarized Surface Bidirectional Reflectance Model Using the Ground-Based Multiangle SpectroPolarimetric Imager

“…The MSPI camera design uses a time-varying retardance in the optical path to modulate the orientation of the linearly polarized component of the incoming light, described by the Stokes components Q (excess of horizontally over vertically polarized light) and U (excess of 45° over 135° polarized light) [23][24][25]. Circular polarization V is typically negligible for natural scenes [26,27].…”

“…Equations (1a) and (1b) are simplified from the more general expressions [24] that include gradients in I, Q, and U, and other terms. Polarized intensity, degree of linear polarization (DOLP), and angle of linear polarization (AOLP), are defined as [22,28]:…”

“…Results from our first prototype camera, LabMSPI, are described in [24]. LabMSPI was a single wavelength (660 nm) camera designed to demonstrate the dual-PEM imaging concept.…”

Spaceborne underwater imaging

“…Conducting experiments to test our theory will require systems under current development such as those in Refs. [5,12].…”

“…We also exploit scientific findings about natural characteristics of water polarization and deep water radiance. We believe this theory can suit a new generation of remote sensing instruments, having multiangular and polarimetric capabilities [5,12], in addition to high spatial resolution.…”