If the drones had transponders that could be tracked in the U-space, and there was an ATM model adopted that could track them, then this wouldn't be a mystery. Thales (<a href="https://www.thalesgroup.com/en/worldwide/aerospace/press_release/thales-and-thaicom-establish-foundation-lead-unmanned-traffic" rel="nofollow">https://www.thalesgroup.com/en/worldwide/aerospace/press_rel...</a>) and Airbus (<a href="https://www.airbus.com/en/innovation/autonomous-connected/airbus-unmanned-traffic-management" rel="nofollow">https://www.airbus.com/en/innovation/autonomous-connected/ai...</a>) both say they have a model that tracks drones, even hobby drones.