A possible candidate is MIR (Micro Impulse Radar), developed at
Lawrence Livermore Labs, at public expense. There is a measly 100K
USD license fee...
Anyway, thought I'd mention it.

http://www-lasers.llnl.gov/lasers/idp/mir/mir.html

Regards, Jack
Allen Foster wrote:
>
> I am currently designing a system to measure the distance between two cars
> when they are moving at speed. Would ultrasonic transducers be suitable for
> the job? I'm a bit worried about what effect the wind will have on them and
> if they will opertae over a long enough range.
>
> Also, does anyone know what mercedes use to measure the distance in their
> cruise control system which measures the distance between cars?