ADS-B — Automatic Dependent Surveillance–Broadcast — is how modern aircraft continuously announce who and where they are. It is the raw material behind every flight tracker, and understanding it is the key to understanding what can be trusted, what can be spoofed, and how AeroScope tells the difference.
The name is the explanation. The transmission is automatic (no interrogation needed), dependent on the aircraft's own navigation systems (typically GPS), it is a form of surveillance, and it is broadcast in the clear for anyone in range to receive. Twice a second, a transponder radiates a small packet containing position, altitude, velocity and identity.
GPS latitude/longitude plus barometric and often geometric (GPS) altitude — the two altitude sources are a key cross-check for integrity.
Ground speed, track angle and vertical rate. Enhanced-surveillance aircraft may also broadcast indicated/true airspeed, Mach and heading.
A unique 24-bit ICAO address and, usually, a flight callsign — the keys AeroScope uses to de-duplicate and to look up registry and military allocations.
NIC, NACp, NACv and SIL describe how trustworthy the position is. They are central to spoofing detection — a fabricated message often gets them wrong.
Most of the world broadcasts ADS-B on 1090 MHz (1090ES, Mode S Extended Squitter). In the United States, many lighter aircraft use 978 MHz UAT (Universal Access Transceiver). AeroScope's feeds cover the 1090 MHz picture globally and UAT where networks republish it.
| Field group | Examples | Why it matters here |
|---|---|---|
| Position | lat, lon, baro alt, geo alt | Drives the map and altitude self-consistency checks |
| Velocity | ground speed, track, vertical rate | Feeds Kalman tracking and envelope checks |
| Identity | ICAO hex, callsign, squawk | Registry, military hex, emergency-squawk alerts |
| Integrity | NIC, NACp, NACv, SIL | The backbone of spoofing / DO-260B integrity scoring |
ADS-B was designed for safety and openness, not security. The messages are not signed or encrypted, so in principle anyone with a transmitter can fabricate one. That is exactly why AeroScope treats every broadcast as a claim to be checked rather than a fact to be trusted:
Read how those checks combine on the threat & attention scoring page, or how the multi-detector layer works on behavioural baselines.