Heavy rain affects object detection by LiDAR sensors

As part of their testing of autonomous vehicles, researchers from WMG at The University of Warwick have simulated and evaluated the performance of LiDAR sensors in rain. Their results have been published in IEEE Sensors Journal.

High-level autonomous vehicles (AVs) are promised by original equipment manufacturers (OEMs) and technology companies to improve road safety as well as bringing economical and societal benefits to us all. High-level AVs rely heavily on LiDAR sensors, which work by emitting numerous narrow beams of near-infrared light with circular/elliptical cross-sections; these can reflect off objects in their trajectories and return to the detector of the LiDAR sensor.

One of the issues of 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, therefore detecting the raindrop as an object. The droplets can also absorb some of the emitted light, degrading the range of performance for the sensors.

Using the WMG 3xD simulator, WMG researchers tested an autonomous vehicle’s LiDAR sensors in different intensities of rain, driving around a simulation of real roads in and around Coventry. They measured the LiDAR sensor’s responses to the rain, making a record of false positive and false negative detections.

They found that as the rain intensity increased it became more difficult for the sensors to detect objects. In a short range from the vehicle (up to 50 m), several rain drops were erroneously detected. In a medium range (50–100 m) this had decreased, but as rainfall increased to up to 50 mm/h, 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,” said WMG’s Dr Valentina Donzella. “This means that future research will have to investigate how to ensure LiDAR sensors can still detect objects sufficiently in noisy environments.

“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.”

Image caption: The WMG 3xD simulator, used to test the LiDAR sensors. Image credit: WMG, University of Warwick.

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