Earlier today I was out spotting Daytona's race week flights when a very stern Volusia County Sheriff came by and spoiled all of our fun. Being less than 500 feet away from Embry Riddle's campus, I thought the police would be a little more lenient about students sporting cameras and scanners. I guess not.

Anyways, at the time I was stopped, I was parked on airport property. There is an undeveloped lot outside of the perimeter fence that the Daytona Beach Airport has been trying for some time to sell as hangar space. The lot is directly accessible by a public road, and is frequently used as overflow parking by the FBO next door. There is absolutely nothing in the lot other than dead grass and a gravel parking lot.
Since the lot is owned by the airport (therefore, the city of Daytona Beach), I had assumed the property was public use, as would be any other road or parking lot. There are no posted "no trespassing" or "no parking" signs, nothing to indicate that the area is off-limits. Therein lies my question.

Legally, what is airport property? Is airport property (outside of the fence, of course), considered public use? I know that you don't need to apply for a permit to use a city road, park, or beach, but what about publicly accessible airport property? Was the sheriff being over-zealous because of the activity near the airport, or was I un-knowingly trespassing on private property?

I directly asked the sheriff if the property was public use and he quickly responded with a "no," but law enforcement officials have blatantly lied to me before when they want me to leave an airport. Is there anyone around that actually knows the legalities of airport property in the US? Am I justified to return to my spotting location, or should I really go elsewhere?

Thanks in advance for any replies.