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Comment by bhousel | Hacker News Reader

Cool. This will be fine as long as 2 self driving cars never go near each other.

Aren't the optical paths highly selective for direction, time, and wavelength? Let's assume coincident-wavelength for our worst case. At any given point in time, it's as if each car has a laser pointer aiming a single dot somewhere, and that single dot is also the only point it's receiving light from (in stark contrast to a camera, which is gathering light from its entire field of view). Even if the LIDARs can see each other, there's no 0-attenuation path from the output of one to the input of another unless a pair of LIDARs have chosen, out of their entire FOV, to aim directly at each other.

So, if we define "traversal time" as the time required for the dot of car A to sweep the aperture of car B, in each traversal time there's 1 chance in N^4 of perfect alignment, where N is the ratio of dot size to the full FOV. Maybe it happens once in a blue moon, but if the sensor can withstand full illumination for more than one traversal time, you would start having to compound 1/N^4 events in order to fry a sensor. I wouldn't count on it.

Well, I wouldn't count on that particular mechanism, at least. I'm sure there will be cases where a coating degrades and lets broad-band sunlight in, or a sensor parks on the sun, etc. Sensors will get fried, but not because the engineers making them were too stupid to consider interference.

from TFA:

>Crucially, self-driving cars also rely on conventional cameras. So if those lidars are not camera-safe, it won't just create a headache for people snapping pictures with handheld cameras. Lidar sensors could also damage the cameras on other self-driving cars.

Shouldn't this also be a problem with other non-passive sensors like radar. If we have a traffic jam of cars each sending radio waves from multiple sensors there has to be quite some interference, no?

Radars pointed at each other may have some interference resulting in temporary erroneous readings but they won't be permanently damaged like the camera in the article.

In a heterogenous environment this is not necessarily true; a radar with a powerful transmitter could damage a radar with a very sensitive receiver, particularly at close ranges.

There are military jamming devices that can quite handily permanently damage radars not designed to distinguish it.

Oh I see, that makes sense. I wonder if any automotive radars are that powerful.

Almost certainly not. The FCC approval process would likely catch that. Lasers are also far more focused then microwaves (typical spot size of a cheapo laser pointer is 12cm at 100m away; police LIDAR is good to target a single car out to at least 1/4 mile).

Tangent: the Soviet MiG-25P interceptor had a 600kW radar which was lethal to small animals if used on the ground.

Self-driving cars use cameras too!

Selecting a pulse repetition interval and spreading sequence from a prng should mostly eliminate interference like that for both lidar and radar I think.

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