Multiple-wavelength range-gated active imaging principle integrating spectral information for five-dimensional imaging.

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. By combining two wavelength categories, it determines the depth of moving objects in the scene with the warm color category and the precise moment of a moving object's position with the cold color category. Therefore, since each object had the ability to transmit information from different wavelengths, related to the spectral reflectances, it became interesting to identify their spectral signatures from these reflectances.

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

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.

Doppler effect in the multiple-wavelength range-gated active imaging up to relativistic speeds.

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.

Combination of the two styles of the multiple-wavelength range-gated active imaging principle for four-dimensional imaging.

Having 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.

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

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.

Multiple-wavelength range-gated active imaging principle in the accumulation mode for three-dimensional imaging.

Having laid the foundations of the multiple-wavelength range-gated active imaging principle in flash mode in a previous paper, we have been studying its use in accumulation mode. Whatever the mode, the principle consists of restoring the 3D scene directly in a single image at the moment of recording with a camera. Each emitted light pulse with a different wavelength corresponds to a visualized zone with a different distance in the scene.

Direct method of three-dimensional imaging using the multiple-wavelength range-gated active imaging principle.

The tomography executed with mono-wavelength active imaging systems uses the recording of several images to restore a three-dimensional (3D) scene. Thus, in order to show the depth in the scene, a different color is attributed to each recorded image. Therefore, the 3D restoration depends on the video frame rate of the camera.

Analysis of the visual artifact in range-gated active imaging, especially in burst mode.

After the demonstration of the occurrence of visual artifacts with an active imaging system in burst mode in a previous paper, the analysis of this phenomenon was realized. A visual artifact resulting from a remote zone in the scene can appear in the image of the real visualized zone when the duty cycle of laser pulses is close to 50%, as in the burst mode. Therefore, the elements of this remote zone will create confusion in the image, with erroneous estimated distances.

Modeling of the visual artifact in range-gated active imaging, especially in burst mode.

An active imaging system in burst mode allows the duty cycle of laser pulses to be close to 50%. In this configuration, a visual artifact resulting from a remote zone in the scene can appear in the image of the desired visualized zone. Therefore, the elements of this remote zone will create confusion in the image with erroneous estimated distances.

Impact of a distance estimation error inducing a visualized zone gap on the target illuminance in range-gated active imaging.

Some stand-alone airborne systems of target reconnaissance such as a missile seeker head use range-gated laser active imaging to visualize a target in the scene. To center the visualized zone on the target, it is important to know the distance between the active imaging system and the target. However, as this exact distance is not known before the detection of the target, it can be only estimated.