Do they still do that?  If so it&#x27;s because they don&#x27;t want to have frequency agility turned on all the time so potential adversaries get less opportunity to figure out the relevant algorithms.  The degree by which radars adjust their pulse frequencies is way larger than the doppler shift of anything you&#x27;re likely to run into traveling in the atmosphere.  You will occasionally have a conflict by chance but radars by their very nature have to deal with a certain amount of noise.<p>With lidars you won&#x27;t be able to adjust frequency because that&#x27;s not how lasers work.  Well, you can with free electron lasers but nobody is going to be putting those in lidars.  But a laser is directional in a way that a laser isn&#x27;t.  You will occasionally get some false returns but real objects persist from scan to scan in a way that noise doesn&#x27;t.  I&#x27;ve worked with a small fleet of lidar equipped robots and lidar cross talk never caused us any problems.  Sunlight on the other hand could be a big problem but automotive lidars are all rated for the outdoors.