Light Transmission in Fog: The Influence of Wavelength on the Extinction Coefficient

Abstract

Featured Application: This work gives some advice on choosing the best wavelengths for active sensors working in the near-infrared spectral band (such as LiDARs or time-of-flight cameras) taking into account fog conditions. Abstract: Autonomous driving is based on innovative technologies that have to ensure that vehicles are driven safely. LiDARs are one of the reference sensors for obstacle detection. However, this technology is affected by adverse weather conditions, especially fog. Different wavelengths are investigated to meet this challenge (905 nm vs. 1550 nm). The influence of wavelength on light transmission in fog is then examined and results reported. A theoretical approach by calculating the extinction coefficient for different wavelengths is presented in comparison to measurements with a spectroradiometer in the range of 350 nm-2450 nm. The experiment took place in the French Cerema PAVIN BPplatform for intelligent vehicles, which makes it possible to reproduce controlled fogs of different density for two types of droplet size distribution. Direct spectroradiometer extinction measurements vary in the same way as the models. Finally, the wavelengths for LiDARs should not be chosen on the basis of fog conditions: there is a small difference (<10%) between the extinction coefficients at 905 nm and 1550 nm for the same emitted power in fog.

Fog Classification by Their Droplet Size Distributions: Application to the Characterization of Cerema’s Platform

“…The Cerema Adverse Weather platform was developed to investigate all transportation systems that could be affected by adverse conditions, including fog and rain [4,9,44]. This 31 m long platform includes a 15 m fixed section (tunnel) and a 16 m greenhouse with a transparent envelope for daytime conditions and an opaque cover for night time conditions.…”

“…It is used to relate to the MOR, noted as V, as shown in Equation 3. It is based on Mie's theory, which gives an extinction coefficient Q ext (r) for each drop of radius r [4]. β is usually expressed in m −1 .…”

“…With the advent of Advanced Driver Assistance Systems (ADAS), and the development of autonomous vehicles, it is very important to take into account the impact of fog on the sensors dedicated to driving. The MOR is always critical, however, as sensors can use different wavelengths, some of which are beyond the visible; the microstructure of the fog is also critical [4]. There are indeed many different Droplet Size Distributions (DSD) of fog [1].…”

A Review and Perspective on Optical Phased Array for Automotive LiDAR

“…Various recent studies have investigated the effect of weather on different wavelengths of LiDAR, particularly of rain and fog. The effect on both wavelengths is similar, as at the same optical power there is a small difference (<10%) between the two [71]- [72].…”

An Overview of Lidar Imaging Systems for Autonomous Vehicles

“…This introduces a large number of false detection alarms from the backscattered intensity, reducing the reliability of the sensor [85,143]. Further, snowflakes, fog and rain droplets have different shapes, distributions and sizes and affect different aspects of the detection, complicating a precise modeling [144]. Managing lidar imaging in extreme weather conditions is a pending subject of the technology which needs to be tackled in the near future for commercial deployment of automated vehicles.…”