Testing and Performance Characterization of the Split-Field Polarimeter in the 3-5 Micrometers Waveband

摘要

The infrared (IR) radiation emitted or reflected in an off-normal direction from a smooth surface is partially polarized. This principle can be used for enhanced discrimination of targets from backgrounds in marine environment. It has been shown that (man-made) targets do not demonstrate a pronounced polarization effect when observed at near normal existence whereas the sea background radiation has a significant degree of polarization in slant observation directions. The NPS split-field polarimeter was previously designed and constructed to provide simultaneous image pairs in a single frame, differing only in the direction of linear polarization. The system can operate in both long wavelength (8-12 micrometers) and the mid wavelength (3-5 micrometers) with interchangeable polarizing splitter plates. In this thesis, tests were conducted to visually compare the polarizing effect on objects in the 3-5 micrometers waveband using the polarimeter and with the external polarizer. The image recorded in the laboratory with the horizontal and vertical polarizations depicts a contrast enhancement differing with varied aspect of the target. With the successful demonstration of the polarimeter operability, the performance of the thermal imager operated with and without the polarimeter was characterized by measuring its Minimum Resolvable Temperature Difference (MRTD) as a function of different spatial frequency. The measured performance was then compared against the same thermal imager using an external polarizer. The measured MRTD curve is used to model the system detection and recognition range using the Johnson criteria.