About LiDAR's rain countermeasures

Due to the nature of LiDAR, which measures the distance by emitting a laser and reflecting it from the target, the effects of rain cannot be avoided, but it is possible to reduce the effects by taking the following measures.

Hokuyo LiDAR is equipped with a multi-echo function. When a laser hits a transparent or translucent object such as glass, rain, or fog, two types of laser may return to the sensor: the laser that is reflected by the transparent object, and the laser that is transmitted by the transparent object and reflected by the object behind it. .
The multi-echo is a function that can acquire distance data only from multiple laser beams returned at the same step angle.
By using this function, it is possible to distinguish rain or fog and the objects that actually want to detect with the returned distance value from the sensor.

Also, in case of the sensor type that sets an area for obstacle detection, data processing is generally difficult, so the echo selection is used by selecting the last echo.

As a point to note, rain is easy to get measurement data at a short distance, but the echo separation characteristics depend on the object and the environment, so separation will not work unless the distance difference between the measured rain and the object is 3m or more.
It may not be possible to measure small objects at short distances.

One point to note about the rain filter is that the response becomes slow due to continuous confirmation.

It is also effective to limit the sensing target to only large objects. The area setting type sensor is able to set the minimum detectable object, and the target to 50 mm or more is effective.
Needless to say, this means that smaller objects cannot be detected.

・LiDAR outputs data with a range 30m and 270°and detects obstacles by area setting