File / belgian-wave-1990
Evidential coreThe Belgian Wave
F-16s with radar recordings against triangles over Belgium — and the correction that changes everything
Over five months thousands of people in Belgium, including gendarmerie officers, reported large, silent triangular objects. On the night of 30/31 March 1990, with correlating ground radar, two F-16s were scrambled and their radars obtained brief contacts.
Official position
The Belgian air force released documentation and participated in the analysis. The case remained unidentified.
Alternative hypotheses
- Artefacts of the F-16 radar tracking filter — later analysis indicated that the abrupt “accelerations” in the recordings match Kalman filter behaviour during a track jump rather than target motion.
- Helicopters, aircraft in unusual lighting configurations and balloons as the source of some ground sightings.
- Classified aircraft (a stealth hypothesis) — never confirmed.
Why this is the best radar lesson in the database
The Belgian wave is remarkably strong as an event and remarkably instructive as an analytical case — because it shows how real data can generate an unreal conclusion.
The F-16 airborne radar recordings genuinely exist and genuinely show abrupt changes in target parameters. For years they were presented as measurements of accelerations impossible for known technology.
Later analysis pointed elsewhere. An F-16 radar does not display the target’s raw position. It displays the output of a tracking filter that smooths and predicts a trajectory. When the filter loses one target and acquires another, a jump appears in the record — and that jump looks exactly like extreme acceleration, while being an artefact of the algorithm.
What this means for the field
Not that the Belgian wave is debunked. Thousands of ground sightings, gendarmerie accounts among them, remain unresolved, and the wave as a whole has no explanation.
It means something more important: we have to know whether we are looking at a measurement or at a software product. The same caution applies to every modern ATFLIR recording and to every track file we have not seen in raw form.
The Petit-Rechain photograph
In 2011 the wave’s most famous image — a triangle with four lights — was admitted by its author, on Belgian television, to be a hoax: painted styrofoam with lights at the corners, hung on threads. In 2022 he was reported as claiming he had been paid to say that.
The retraction has no documentary support, and it does not rescue the photograph either way. An image whose own author has given two contradictory accounts of making it cannot carry evidential weight. We treat it as a T5 source of zero value and record the whole sequence because the image is still reproduced as evidence.
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