The atmosphere is monitored by a patchwork of systems: NOAA's weather observation network, the FAA's radar and ADS-B infrastructure, EPA air quality monitors, and volunteer-operated networks like ADS-B Exchange. Each captures a different slice of what moves through the sky.

The gaps

No single system captures everything. Military aircraft often fly without ADS-B transponders. Private aircraft can request blocked callsigns. Low-altitude operations may not appear in commercial flight data at all. Observation is about working with what is visible and being honest about what is not.