From ground-based radar to satellite surveillance — a complete guide to how aircraft are tracked across the globe in real-time.
Flight tracking has evolved dramatically since the mid-20th century. What began with primitive radio direction-finding has become a global network of sensors, satellites, and software capable of tracking tens of thousands of aircraft simultaneously.
The oldest form of aircraft detection. A ground station transmits powerful radio pulses and listens for reflections from aircraft. PSR can detect any object — even those without a transponder — but provides only position (range + bearing) with no identity or altitude information. Range: 60-200 nautical miles. Still used at major airports as a backup.
An improvement over PSR. The ground station transmits an "interrogation" signal, and aircraft transponders reply with coded information. Three modes exist:
| Mode | Data Transmitted | Era |
|---|---|---|
| Mode A | 4-digit squawk code (identity) | 1960s |
| Mode C | Squawk code + pressure altitude | 1970s |
| Mode S | 24-bit ICAO address + altitude + selective interrogation | 1990s |
Mode S is the foundation for modern ADS-B. Each aircraft has a unique 24-bit ICAO address (like a MAC address for airplanes), enabling individual identification without relying on squawk codes.
Automatic Dependent Surveillance — Broadcast (ADS-B) is the current global standard. Unlike radar (which requires ground infrastructure to interrogate), ADS-B is automatic — aircraft continuously broadcast their position, altitude, speed, heading, and identity on 1090 MHz. Anyone with a simple receiver can pick up these signals.
Key characteristics:
ADS-B transmits: ICAO hex address, latitude, longitude, barometric altitude, ground speed, track heading, vertical rate, callsign, squawk code, aircraft category, and integrity parameters (NIC, NAC, SIL). Update rate: every 0.5-2 seconds.
The FAA mandated ADS-B Out for most controlled airspace in the US as of January 1, 2020. EASA has similar requirements in Europe. This is why most commercial aircraft are now trackable via ADS-B.
For aircraft that transmit Mode S but not full ADS-B position data, multilateration can calculate position by measuring the Time Difference of Arrival (TDOA) of signals at 4+ ground receivers. This enables tracking of older aircraft that have Mode S transponders but no GPS-based ADS-B Out. Accuracy: typically 50-500 meters.
The newest layer. Companies like Aireon have placed ADS-B receivers on Iridium NEXT satellites, enabling global coverage — including over oceans, poles, and remote areas where ground receivers don't exist. This closed the last major gap in flight tracking and was a direct response to the MH370 disappearance in 2014.
Platforms like AeroScope aggregate data from thousands of volunteer-operated ADS-B receivers worldwide. Anyone can set up a receiver for under $50 (RTL-SDR dongle + antenna) and feed data to community networks. This creates comprehensive coverage that rivals commercial systems. AeroScope uses data from adsb.fi, adsb.lol, and OpenSky Network.
AeroScope ingests ADS-B data from multiple community networks in parallel, deduplicates by ICAO address, and runs a 15-stage enrichment pipeline that adds threat scoring, drone detection, pattern analysis, signal integrity assessment, emissions calculation, and predictive trajectory modeling — all in real-time, every 12 seconds.