Case FR-24/09 — Composite Anomaly in Coastal Sector (Île d’Ouessant, Finistère)
Date: 14 September 2024
Location: Île d’Ouessant, Brittany, France — 48°28′51″N, 5°03′57″W
Weather Conditions: Clear sky, visibility 26 km, W wind 15 km/h, humidity 67%
Reports: 5 independent (3 civilian, 2 technical)
Technical Detections: RSR-220 coastal radar, underwater acoustic sensor array, maritime meteorological logs
Event Summary
At 21:56 local time, two operators at the Phare du Stiff radar station reported the presence of an anomalous contact approximately 8.2 km northeast of the island, in open sea. The radar echo displayed intermittent tracking with sudden fluctuations in radar cross-section (RCS), with no associated transponder emissions or AIS signals.
Seconds later, three civilians in different locations on the island (north and west sectors) observed three luminous sources aligned along an oblique axis, moving slowly relative to one another, increasing and decreasing in brightness synchronously. Simultaneously, a hydrophone from the port’s underwater monitoring network recorded a sequence of low-frequency pulses originating from the same bearing as the radar contact.
Event Timeline
- 21:56:12 — Initial radar detection from Phare du Stiff, sector 045°, distance 8.2 km, initial RCS 4.8 m².
- 21:57:03 — Independent visual observation from Pen ar Lan promontory: three white lights, visually estimated distance 6–8 km, oblique arrangement at ~25° angle.
- 21:57:41 — Radar echo fragments into three distinct returns, each with variable RCS (2.9–5.4 m²), maintaining constant relative position.
- 21:58:26 — Civilian witness from western sector: same three lights, visible pulsing, no audible noise.
- 21:59:12 — Port hydrophone records 42 Hz pulse, 2.6 s duration, followed by five irregular pulses (intervals 1.2–1.7 s).
- 22:00:05 — Lights observed from northern sector increase sharply in intensity, then fade and vanish within 4–5 seconds.
- 22:00:48 — Final radar contact loss. Last acoustic pulse recorded at 22:01:10.
Radar Analysis
The RSR-220 coastal radar recorded rapid RCS variations, averaging oscillations every 0.5 seconds. The three distinct returns in the second phase do not match separation patterns consistent with aircraft formations, multiple drones, or bird flocks.
No IFF response or Mode-S emissions were detected, and checks with civilian and military air traffic records showed no transits in the area during the time window.
Acoustic Analysis
The 42 Hz signal recorded by the hydrophone displayed non-constant amplitude modulation, with secondary harmonics at 81 Hz and 124 Hz. Estimated bearing matches the radar contact sector.
No operational naval units were in proximity at the time, and spectral profile comparisons with the region’s acoustic database yielded no matches.
Witness Statements
Radar Operator (anonymous):
“The contact was stable for a few seconds, then split into three distinct returns. No known flight behaviour produces such clean fragmentation while maintaining fixed relative positioning.”
Civilian Witness (J. L., Ouessant resident):
“They looked like three very close white stars, but they pulsed as if following a rhythm. Then they all vanished together, as if someone had thrown a switch.”
Environmental Data and Correlations
- Meteorology: No refractive anomalies, no significant thermal inversions.
- Maritime Traffic: No AIS transits recorded at the detected coordinates.
- Seismology: No anomalous activity within the previous 24 hours.
- Local Magnetic Field: Within normal variation.
Internal Assessment
The event displays a composite nature: the temporal coincidence of radar, visual, and acoustic detections significantly reduces the probability of a conventional explanation.
Two primary working scenarios:
- Unidentified Aerial Phenomenon capable of generating multiple radar returns and underwater acoustic emissions.
- Combined Air–Subsurface Origin, involving two or more synchronised sources.
The absence of photographic evidence limits further verification, but triple detection from independent sensors keeps the case at high priority.
Case Status: Active — Under Monitoring
Internal Classification: Type II-B — Multi-modal event with no conventional correlates
Estimated Probability of Conventional Origin: <20%
Technical Appendix — Case FR-24/09
1. Detailed Radar Parameters (RSR-220)
| Timestamp (local time) | RCS (m² eq.) | Return Type | Azimuth (°) | Distance (km) | Coherence Notes |
|---|---|---|---|---|---|
| 21:56:12 | 4.8 | Single | 045 | 8.2 | 100% coherent |
| 21:56:43 | 4.5 | Single | 045 | 8.2 | Brief amplitude fluctuation |
| 21:57:41 | 3.7/5.4/2.9 | Triple | 044–046 | 8.1–8.3 | Fixed relative position, fragmented returns |
| 21:58:04 | 5.1/4.0/3.2 | Triple | 045 | 8.2 | Stable radial coherence, amplitude modulation present |
| 21:59:50 | 3.6 | Single | 045 | 8.3 | Attenuation to contact loss |
Note: The fragmentation into three distinct returns did not involve angular or radial divergence sufficient to indicate three physically separate craft, suggesting multiple reflections or anomalous scattering from a single source.
2. Acoustic Parameters (Port Hydrophone Network)
| Pulse No. | Fundamental Frequency (Hz) | Harmonic 1 (Hz) | Harmonic 2 (Hz) | Duration (s) | Next Interval (s) | RMS Intensity (dB) |
|---|---|---|---|---|---|---|
| 1 | 42.0 | 81.3 | 124.2 | 2.6 | 1.4 | -86 |
| 2 | 42.1 | 81.0 | 124.5 | 2.4 | 1.3 | -84 |
| 3 | 42.0 | 81.2 | 124.3 | 2.3 | 1.5 | -85 |
| 4 | 42.2 | 81.4 | 124.1 | 2.6 | 1.2 | -83 |
| 5 | 42.0 | 81.1 | 124.4 | 2.5 | — | -84 |
Observations:
- Non-constant amplitude modulation with slight frequency shifts (±0.2 Hz).
- No match with known local marine fauna or naval mechanical sources over the past 5 years.
- Stable harmonics are consistent with an artificial source or induced resonance.
3. Recorded Environmental Conditions
| Parameter | Recorded Value | Notes |
|---|---|---|
| Air Temperature | 17.3 °C | Stable from 20:00 to 23:00 |
| Water Temperature | 14.8 °C | Stable |
| Atmospheric Pressure | 1018.7 hPa | Slightly increasing |
| Wind Direction | 272° (W) | 15 km/h constant |
| Relative Humidity | 67% | No significant variation |
| Sea State | Beaufort 2 | Wave height 0.5 m |
4. Multi-Sensor Coherence Analysis
Temporal overlap between radar, optical, and acoustic channels is accurate to within ±3 seconds. Probability of random coincidence: <3.5% (Protocol 09-MX).
5. Updated Operational Hypotheses
- Scenario A: Single airborne multi-emission source.
- Scenario B: Integrated air–sea system.
- Scenario C: Anomalous physical phenomenon.
Provisional Technical Conclusion: Classification confirmed as Type II-B. Case file remains open pending new reports from the same sector.
