Spectropolarimetric imaging using a field-portable imager

The Army Research Laboratory has a program to develop and characterize compact field-portable hyperspectral and polarization imagers using electronically tunable spectral filters—acousto-optic tunable filters (AOTFs)—that are polarization sensitive. A spectropolarimetric imager has been designed that combines a liquid-crystal retardation plate with an AOTF and an off-the-shelf charge coupled device (CCD) camera. The imager uses a tellurium dioxide (TeO2) AOTF that operates from the visible to the near-infrared region. The imager is relatively compact, lightweight, and programmable. We used this imager to collect spectral and polarization data from various objects and backgrounds, both in the laboratory and in field tests. The spectral images were collected from 450 to 1000 nm at 10- or 20-nm intervals, at two or four polarization settings for each spectral interval. We analyzed a portion of these data to assess the effectiveness of this system for target detection and identification. Here we present and discuss our measurements and analysis results.