Researchers from the University of Warwick (WMG) are testing how lidar sensors on vehicles perform in the rain.
Using a WMG 3xD simulator, the team tested an autonomous vehicle’s lidar sensors in different intensities of rain, driving around a simulation of real roads in and around Coventry, U.K.
One of the issues with lidar sensors is the degradation of its performance in rain. If a lidar beam intersects with a raindrop at a short distance from the transmitter, the raindrop can reflect enough of the beam back to the receiver, detecting the raindrop as an object. The droplets can also absorb some of the emitted light, degrading the range of performance for the sensors.
Lidar works by emitting numerous narrow beams of near-infrared light with circular/elliptical cross sections that reflect off objects in their trajectories and return to the detector of the lidar sensor.
Researchers, using different rain models, made it rain on the WMG 3XD simulator and measured the lidar sensor’s responses in the rain, making a record of false positive and false negative detections.
As the rain intensity increased, it became more difficult for the sensors to detect objects. At a short range (up to 50 meters), several rain drops were erroneously detected. At medium range (50 to 100 meters) this decreased but as rainfall increased up to 50 mm per hour, the sensors’ detection of objects decreased in conjunction with a longer range in distance.
"Ultimately we have confirmed that the detection of objects is hindered to LiDAR sensors the heavier the rain and the further away they are, this means that future research will have to investigate how to ensure LiDAR sensors can still detect objects sufficiently in noisy environment,” said Valentina Donzella from the University of Warwick. "The developed real-time sensor and noise models will help to further investigate these aspects, and may also inform autonomous vehicles manufacturers' design choices, as more than one type of sensor will be needed to ensure the vehicle can detect objects in heavy rain."
The full research can be found in the journal IEEE Sensors.