"SPEAR - A LWIR POLARIMETRIC HYPERSPECTRAL IMAGER WITH PERFECT CHANNEL REGISTRATION: SENSOR DESIGN, SIGNAL PROCESSING AND FIELD TEST RESULTS," S. Jones, F. Iannarilli, Jr., H. Scott,P. Kebabian, J. Mello, R. Lockwood, and S. Lipson, Proc. MSS Passive Sensors, (2000).
Polarimetric and hyperspectral imaging in the long wave infrared (LWIR) offer distinct advantages for a wide range of detection and classification problems. Polarimetric imaging yields target information primarily related to surface smoothness and orientation while hyperspectral information is more closely related to the target material composition. In the past, polarimetric imagers have suffered the from the shortcomings of temporal misregistration, due to a rotating analyzers and retarders, or spatial misregistration, due to stationary but spatially separated analyzers and retarders. The SpectroPolarimeter for Enhanced Aerospace Reconnaissance (SPEAR) sensor overcomes these shortcomings by a novel optical design that encodes polarimetric information onto the spectrum, thereby achieving perfect registration, temporally, spatially, and spectrally.
The prototype SPEAR sensor is currently being developed under an ongoing Phase 2 SBIR through AFRL/VSBM. The nominal operating band is 7.5-11.5 microns, chosen based on the atmospheric transparency in this region, target spectral features of interest, and the achievable long wave cutoff at the design operating temperature of 55 degrees Kelvin. The imaging spectrometer uses an Offner relay design that significantly reduces optical aberrations compared to the more common Czerny-Turner off-axis toroidal mirror designs. The prototype sensor has been designed to yield effective polarimetry at a range of 10 km and includes a 800 mm f/3 Ritchey-Chretien telescope.