Here's a link to a 'techie' explanation that is more layman's terms readable.
http://www.tritech.co.uk/chirpCHIRP btw is an acronym for
Compressed High Intensity Radar Pulse, commonly now used to refer to the sweep spectrum technology that the industry settled on. CHIRP is the affectionate term the industry is using for the sweep spectrum signalling being used vs. the single frequency of past.