Application of LADAR in the Analysis of Aggregate Characteristics (2012) / Chapter Skim
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4This chapter presents the design configuration of the FTI aggregate imaging and analysis system. The FTI system is actually a noncontact 3-D surface profilometer, using a simple fiber optic coupler to form a Young's double-pinhole interferometer.
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5 The aggregate is placed on an adjustable-height tray (shown in Figure 2-6) , and users can move the surface into the field of view to maximize the clarity of images.
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6Figure 2-3. Fringe source: fiber-coupled laser sources and 1 2 fiber switch.
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7 Once the reference fringe order is determined, it must be applied to the unwrapped phase map ju(x, y) , calculated only once for the entire image, regardless of surface boundary or reference fringe selection.
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8Startt rt Image acquisition in FTI systemI i iti i I t Input images in FTI software Map surface boundaries Choose reference fringe Track fringe Determine fringe order Pre-filter fringe images Shift phase Basic FTI algorithm Calibration matrices Calculate surface profile Surface error correctionrf rr r rr ti Narrow boundary windowingrr r i i Convert to relative heightrt t r l ti i t Output data of 3D coordinatest t t f r i t Original z(x,y) Two-dimensional Fourier Analysis Sphericity, Flatness ratio, Elongation ratio, Angularity, Texture End Choose alternative fringe Track fringe Determine fringe order Input height of particle tray z'(x,y)
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9 610 615 620 625 630 635 640 645 650 0 2000 4000 6000 8000 10000 12000 14000 16000 Fringe Track Fitting: Painted Glass Target @ 808nm, row 300 Fringe Data Peak Fit Figure 2-10. Narrow window curve fitting during fringe peak tracking (Lally, 2010)
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11 Figure 2-14. Quality of fringes generated with fiber coupler: calibration coefficient deviation (left)
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12 HeNe laser wavelength of 633 nm. Such glasses are relatively inexpensive and widely available.
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