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25 September 2007 Robust optical alignment systems using geometric invariants
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Abstract
Traditional coarse pointing, acquisition, and tracking (CPAT) systems are pre-calibrated to have the center pixel of the camera aligned to the laser pointing vector and the center pixel is manually moved to the target of interest to complete the alignment process. Such a system has previously demonstrated its capability in aligning with distant targets and the pointing accuracy is on the order of sensor resolution. However, aligning with targets at medium range where the distance between angular sensor and transceiver is not negligible is its Achilles Heel. This limitation can be resolved by imposing constraints, such as the trifocal tensor (TT), which is deduced from the geometrical dependence between cameras and transceivers. Two autonomous CPAT systems are introduced for FSO transceiver alignment in mid- and long-range scenarios. This work focuses on experimental results that validate the pointing performance for targets at different distances, backed up by the theoretical derivations. A mid-range CPAT system, applying a trifocal tensor as its geometric invariant, includes two perspective cameras as sensors to perceive target distances. The long-range CPAT system, applying linear mapping as the invariant, requires only one camera to determine the pointing angle. Calibration procedures for both systems are robust to measurement noise and the resulting system can autonomously point to a target of interest with a high accuracy, which is also on the order of sensor resolution. The results of this work are not only beneficial to the design of CPAT systems for FSO transceiver alignment, but also in new applications such as surveillance and navigation.
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Tzung-Hsien Ho, John Rzasa, Stuart D. Milner, and Christopher C. Davis "Robust optical alignment systems using geometric invariants", Proc. SPIE 6709, Free-Space Laser Communications VII, 670907 (25 September 2007); https://doi.org/10.1117/12.739101
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