Radar isnt really an option if you go for simple time of flight measurement,round our way light and radio waves travel at 186000 miles /second which is approx
300000000 meters/second which is a little bit fast if you want any kind of resolution.Traffic radars use Doppler shift measurements because the target is moving relativly quickly.Sound waves pinging off your target go at 431 meters/second at sea level which is a little bit easier to deal with but again subject to variation due to temp/pressure/windspeed and what colour underwear you have on.