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12 September 2003 Radiometrically calibrating spectrally coupled two-color projectors
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Infrared projection systems based on resistor arrays typically produce radiometric outputs with wavelengths that range from less than 3 microns to more than 12 microns. This makes it possible to test infrared sensors with spectral responsivity anywhere in this range. Two resistor-array projectors optically folded together can stimulate the two bands of a 2-color sensor. If the wavebands of the sensor are separated well enough, it is possible to fold the projected images together with a dichroic beam combiner (perhaps also using spectral filters in front of each resistor array) so that each resistor array independently stimulates one band of the sensor. If the wavebands are independently stimulated, it is simple to perform radiometric calibrations of both projector wavebands. In some sensors, the wavebands are strongly overlapping, and driving one of the resistor arrays stimulates both bands of the unit-under-test (UUT). This “coupling” of the two bands causes errors in the radiance levels measured by the sensor, if the projector bands are calibrated one at a time. If the coupling between the bands is known, it is possible to preprocess the driving images to effectively decouple the bands. This requires performing transformations, which read both driving images (one in each of the two bands) and judiciously adjusting both projectors to give the desired radiance in both bands. With this transformation included, the projection system acts as if the bands were decoupled - varying one input radiance at a time only produces a change in the corresponding band of the sensor. This paper describes techniques that have been developed to perform radiometric calibrations of spectrally coupled, 2-color projector/sensor systems. Also presented in the paper are results of tests performed to demonstrate the performance of the calibration techniques. Possible hardware and algorithms for performing the transformation in real-time are also presented.
© (2003) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
David S. Flynn, Richard Bryan Sisko, Breck A. Sieglinger, and Rhoe A. Thompson "Radiometrically calibrating spectrally coupled two-color projectors", Proc. SPIE 5092, Technologies for Synthetic Environments: Hardware-in-the-Loop Testing VIII, (12 September 2003);

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