When operating outside of radar coverage, ADS-B derived ATS surveillance services are provided to operators of aircraft that are ADS-B Out enabled, whilst within the coverage volume of commissioned ADS-B ground stations.
ADS-B ground stations are line-of-sight facilities. The ability for a ground station to received ADS-B data from an aircraft depends on altitude, distance from the site and obstructing terrain. Coverage exists near the surface within 20 nautical miles of the ground station. High level coverage can exceed 250 nautical miles.
In airspace where ADS-B coverage overlaps radar coverage, the radar derived aircraft position will be displayed to ATC.
ADS-B only coverage charts (as at January 2017) at various altitudes are available below (click for full size image):
Refer to active NOTAMs for advice on ground stations in operation