chirp signal

http://en.wikipedia.org/wiki/Chirp

I remember from the time of the Morse code operators that, limiting the bandwith of a pulse train (as in a Morse code transmission) would produce what they would call chirping. That was avoided by increasing the bandwidth of the system, so the third harmonic of the signal was send unattenuated (remember that rectangular signals have only odd harmonics).

There is also the chirping that is used in lasers to get ultrahigh intensity by optical pulse shortening.

http://www.google.ca/search?hl=en&q=laser+%2Bchirp&btnG=Google+Search&meta=

Not just lasers. Chirps are useful in radars. Change the frequency over time, with a limited peak power. When the signal is recieved, delay the signal as a function of frequency, so the signal piles up into a short, high power pulse. That processing increases the detectability of a weak signal and improves the range resolution.

Yes, I see how that would work, bit how do they allocate a time to this compressed pulse, as the object may not be uniformly reflective at all frequencies so there would be under/over reporting = ambiguity in position. I can see there would be less ambiguity about the existence of the target as it may not be detectable without the chirping

The target doesn't have to be uniformly relective, and that would be a very small cause for error, compared with other large problems. Suggest you check out a standard text on radar design, chirps, doppler processing, etc.