Analysis of the performance of a polarized LiDAR imager in fog

Abstract

This paper focuses on exploring ways to improve the performance of LiDAR imagers through fog. One of the known weaknesses of LiDAR technology is the lack of tolerance to adverse environmental conditions, such as the presence of fog, which hampers the future development of LiDAR in several markets. Within this paper, a LiDAR unit is designed and constructed to be able to apply temporal and polarimetric discrimination for detecting the number of signal photons received with detailed control of its temporal and spatial distribution under co-polarized and cross-polarized configurations. The system is evaluated using different experiments in a macro-scale fog chamber under controlled fog conditions. Using the complete digitization of the acquired signals, we analyze the natural light media response, to see that due to its characteristics it could be directly filtered out. Moreover, we confirm that there exists a polarization memory effect, which, by using a polarimetric cross-configuration detector, allows improvement of object detection in point clouds. These results are useful for applications related to computer vision, in fields like autonomous vehicles or outdoor surveillance where many variable types of environmental conditions may be present.

Temporal behavior and processing of the LiDAR signal in fog

“…This signal is expected to follow the shape of a Gamma distribution, and to be fixed in position. It was also observed that the higher the optical densities, the stronger the amplitude of the backscattered signal 8 .…”

“…In scattering environments, active imagers detect a first undesired intense backscattering signal originating from the dispersive medium. In the case of a LiDAR system, such backscattering is caused by the active emission of the laser pulses 8 . This kind of signal may saturate the detector and/or hide the detection of the fainter signals coming back from the actual objects of interest in the scene.…”

A LiDAR imaging system using temporal and polarization discrimination for turbid media

“…We experimentally characterized this state and found that it had a 99.7% degree of circular polarization. The detection configuration is interchangeable between a co-polarized channel or co-channel (left-hand circular polarization) and a cross-polarized channel or cross-channel (right-hand circular polarization) channel 5 .…”

Multimodal imaging sensor based on lidar for advanced perception tasks

“…Our target was to test the system under controlled fog conditions in the facilities at Centre d' Études et d'expertise sur les Risques, l'Environnement, la Mobilité et l'Aménagement (CEREMA). 22,23 Turbid media highly scatters and absorbs light so the denser the media, the shorter the light can penetrate through because the amount of absorbing and scattering events increase. Hence, visibility defined as the maximum distance at which an object can be perceived decreases with the density of the media.…”