Multiple-wavelength range-gated active imaging applied to the evaluation of simultaneous movement of millimeter-size objects moving in a given volume

Abstract

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. Therefore, it was important to evaluate this new context in the case of millimeter-size objects moving simultaneously in a reduced volume. Based on the rainbow volume velocimetry method, the combined WRAI principle was studied in accelerometry and velocimetry with four-dimensional images of millimeter-size objects. This basic principle combining two wavelength categories determines the depth of moving objects in the scene with the warm color category and the precise moment of moving objects position with the cold color category. The difference in this new, to the best of our knowledge, method is at the level of the scene illumination, which is obtained transversally by a pulsed light source having a wide spectral band limited in warm colors in order to get a better depth resolution. For cold colors, the illumination with pulsed beams of distinct wavelengths remains unchanged. Thus, it is possible independently of the video frequency to know from a single recorded image the trajectory, the speed, and the acceleration of millimeter-size objects moving simultaneously in 3D space and also the chronology of their passages. The experimental tests validated this modified multiple-wavelength range-gated active imaging method and confirmed the possibility of avoiding confusion when the object trajectories intersect.