Chase Car
I have actually been in that car as the driver (another pilot), one hand on the wheel, one hand holding a fist mic, accelerates hell for leather from a standing start to god knows how fast on the perry track, power slides onto the runway, and chases the aircraft down the runway probably only 10-20m behind it, calling out the heights to the pilot. 'twas a great adrenaline rush, I can tell you!
It is indeed to assist the pilot in judging height to touchdown, as he cannot see over the long nose on landing.