Multiple-wavelength range-gated active imaging in superimposed style for moving object tracking.

Abstract

Having laid down previously the foundations of the multiple-wavelength range-gated active imaging (WRAI) principle in flash mode and accumulation mode, its use in superimposed style for the direct tracking of moving objects was studied. The movement is supposed to be in a transverse plane of the scene. Each emitted laser pulse with a different wavelength visualizes the object at a specific time. Therefore, the wavelength set allows us to freeze the different positions of the object in the recorded image according to the laser emission period. Thus, in each recorded image, the object trajectory can be visualized directly according to these specific moments, allowing us to deduce the speed and the acceleration of the object at the same time. Another advantage, especially when the object trajectory is unpredictable, is that the wavelength progression indicates the trajectory direction. The principle being independent of the video frequency, the object speed can be very high. Furthermore, the range gating allows improvement of the object visibility through scattering environments. Three cases were identified and studied in superimposed style. Although the first case has not been used with range gating, it allowed us to show the possibility of using a traditional color camera. On the other hand, the two cases applying range gating required management of the exposure time. In each case, the temporal behavior was studied, as well as the possible speeds according to the object distance. The experimental test results validated the theoretical part and the possibility to determine the trajectory and the speed of a moving object with the WRAI principle in superimposed style.