Did you have your phone on you? Turns out Googles mechanics have a good pretty good gps tracking mechanism that records your movement and you might be able to look up the history of the route you were driving? just a thought, but you could use the time positioning details to bascially calculate speed showing you were traveling at a lawful speed and not over the speed limit. Besides that, I'd also consider going to court, just by showing up it's almost gauranteed to get the ticket reduced and if the officer doesn't show up to court then it'll probably been even better.