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The combined multiple-wavelength range-gated active imaging (WRAI) principle is able to determine the position of a moving object in a four-dimensional space and to deduce its trajectory and its speed independently of the video frequency. However, when the scene size is reduced and the objects have a millimeter size, the temporal values intervening on the depth of the visualized zone in the scene cannot be reduced further because of technological limitations. To improve the depth resolution, the illumination type of the juxtaposed style of this principle has been modified.
View Article and Find Full Text PDFDoppler effect in the multiple-wavelength range-gated active imaging up to relativistic speeds.
J Opt Soc Am A Opt Image Sci Vis
March 2022
Having laid down previously the foundations of the combined multiple-wavelength range-gated active imaging (WRAI) principle recording a moving object in a four-dimensional space represented by a single image, it was necessary to know if a Doppler effect could appear in the direction of the radial velocity of the object. This is due to the fact that this imaging principle requires the emission of laser pulses at a certain frequency in relation to this speed. To know the limits, the radial velocity of the object was supposed to go up to relativistic speeds.
View Article and Find Full Text PDFHaving previously reported the foundations of the multiple-wavelength range-gated active imaging (WRAI) principle in juxtaposed style and in superimposed style, its use in combination of both styles was studied. The juxtaposed style consists of restoring the 3D scene directly. Each emitted light pulse with a different wavelength corresponds to a visualized zone with a different distance in the scene.
View Article and Find Full Text PDFThe ranging performance for Geiger-mode avalanche photodiode (Gm-APD) laser detection and ranging (ladar) is mainly evaluated by range accuracy and precision; although Gm-APD ladar can evaluate the ranging performance of the exact position, it is not helpful to comprehensively evaluate the influence on the ranging of each parameter in the whole gate. Due to the target echo's stochastic trigger making the delay adjustment inaccurate, the position of the echo in the gate is stochastic in the actual detection process, so the theoretical calculation may not be able to make ladar ranging performance clear. As to this question, based on the central limit theorem, and assuming the position of the target in the gate obeys Gaussian distribution, while also combining the Gm-APD triggering probability model, we propose the mean ranging accuracy and precision theory to objectively evaluate the ranging performance.
View Article and Find Full Text PDFA CMOS single-photon avalanche diode (SPAD) quanta image sensor is used to reconstruct depth and intensity profiles when operating in a range-gated mode used in conjunction with pulsed laser illumination. By designing the CMOS SPAD array to acquire photons within a pre-determined temporal gate, the need for timing circuitry was avoided and it was therefore possible to have an enhanced fill factor (61% in this case) and a frame rate (100,000 frames per second) that is more difficult to achieve in a SPAD array which uses time-correlated single-photon counting. When coupled with appropriate image reconstruction algorithms, millimeter resolution depth profiles were achieved by iterating through a sequence of temporal delay steps in synchronization with laser illumination pulses.
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