600ft is too low for primary air traffic service radars. Radar installations are placed on high ground and look upwards, there is too much "noise" near the ground for them to be any use. They are intended to assist in deconflicting and dispatching search and rescue for aircraft, and laws generally prohibit aircraft flying below 500ft other than during take off or landing. The radar at the local airport I fly from (or did when such things were possible) can't see aircraft below about 1400ft. As such a drone flying at 600ft is literally under the radar.
Biting the hand that feeds IT
