POLARIMETER WITH MULTIPLE INDEPENDENT TUNABLE CHANNELS AND METHOD FOR MATERIAL AND OBJECT CLASSIFICATION AND RECOGNITION

Embodiments of an active or laser polarimeter are disclosed that transmit multiple independent and tunable temporally-multiplexed polarization states and record or image, at video rates if necessary, the polarized intensity or irradiance reflected or transmitted by objects illuminated by those states, and apply the recorded data to material and/or object classification and recognition using classification algorithms that exploit features of polarization signatures dependent on material type, texture, and/or object shape. The polarimeter also generally records and utilizes one or more passive polarization measurements in order to realize a hybrid active-passive polarimeter. The polarimeter channels are configured and tuned to access multi-dimensional signature spaces specified by existing signature models and/or measurements, with polarization-modulator settings derived by a newly-disclosed subspace-projection algorithm that maximizes a target contrast parameter. Multiple independent polarization channels allow the new polarimeter to outperform conventional two-channel polarimeters, while the subspace-projection algorithm allows the number of channels to be minimized in order to minimize sensor size, weight, and power (SWaP) and maximize speed. Multiple channels are realized by multiplexing among independent transmitter polarization states with one or more high-speed multiplexers, in one embodiment a set of fold-mirror assemblies in the transmitter among which the laser beam is switched by one or more galvanometer scanners fitted in one embodiment with a newly-disclosed composite mirror. The method for material and object classification and recognition includes the maximally-biased classifier derived by the subspace-projection algorithm applied to a single target Mueller matrix, and methods to generalize the classifier.