I believe they need the lines. Since it takes two photos a fixed time period apart the distance travelled between the two photos (using the lines as markers) gives your speed as a backup measurement. Without this you could argue in court that the radar reading was miscalibrated or otherwise incorrect.
The radar does use Dopplar shift, in that any wave refected of a retreating object will present a lower frequency than one reflecting off an advancing object.
When astronomical objects are measured it's expressed as Red Shift (where the light seen seems more towards red than normal because its moving towards us, presenting a higher frequency) - or blue shift which is the exact opposite.
Speed cameras do not measure the time taken for the radar to bounce off your vehicle as the time it would take would be in the magnitude of nanoseconds - requiring one heck of a processor or cycle speed to be remotely accurate. They send out a fixed frequency wave and compare it with the Dopplar shifted one bounced back.
The radar in a Gatso will record your speed once only and then choose whether or not to trigger the two photos. These motorcyclists speed thru the radar check then decelerate very quickly. Although the radar might read 60 in a 30mph zone and therefore trigger the photos, the bike can be slowed in time to have barely travelled between the two photo frames, hence creating the illusion that the radar reading is completely stuffed.
The radar does use Dopplar shift, in that any wave refected of a retreating object will present a lower frequency than one reflecting off an advancing object.
When astronomical objects are measured it's expressed as Red Shift (where the light seen seems more towards red than normal because its moving towards us, presenting a higher frequency) - or blue shift which is the exact opposite.
Speed cameras do not measure the time taken for the radar to bounce off your vehicle as the time it would take would be in the magnitude of nanoseconds - requiring one heck of a processor or cycle speed to be remotely accurate. They send out a fixed frequency wave and compare it with the Dopplar shifted one bounced back.
The radar in a Gatso will record your speed once only and then choose whether or not to trigger the two photos. These motorcyclists speed thru the radar check then decelerate very quickly. Although the radar might read 60 in a 30mph zone and therefore trigger the photos, the bike can be slowed in time to have barely travelled between the two photo frames, hence creating the illusion that the radar reading is completely stuffed.
