PARIS (75) 19.09.2024

On Thursday 19 September 2024, shortly before 10:30, a witness waiting for a meeting photographed the Eiffel Tower and distant La Défense from a sixth-floor room in Paris's 15th arrondissement. The sky was clear and visibility good. He took a photograph at 10:27 and another 2–5 seconds later using 10× optical zoom. Enlarging the second image, he noticed a shape between the Eiffel Tower and the La Défense towers. It was absent from the first photograph, and he could not see it directly through the window immediately afterwards. He stopped looking when colleagues arrived at about 10:30. The sunlit shape appeared relatively flat, yellow underneath and black above. He estimated a distance of 2–8 km and a size of several metres, but could not confirm either and acknowledged that it might be smaller and closer. A Flightradar24 search identified no aircraft that could explain it. After the meeting, at about 12:12, he took more photographs containing aircraft whose appearance was entirely different. He submitted a completed technical questionnaire to GEIPAN on 29 September 2024. GEIPAN judged the case to have good evidential support from the detailed description and photographs. It defines evidential support as the amount of information collected for an account that is considered reliable and objectively established. The preferred explanation was a bird passing rapidly through the camera's field of view. The observation was photographic only, and the object was absent a few seconds earlier. GEIPAN explained that even with the short exposure of 0.0078 seconds, rapid movement could artificially elongate an image in its direction of travel, here horizontally, as seen in the UAP. It could also blur black tones towards grey, affecting radiometric estimates. A great tit was considered a possible source: a small yellow-and-black bird present within Paris, including in September. Using its IPACO image authentication and processing software, GEIPAN compared luminance variations to estimate the object's distance relative to landscape features (Annex 1). It cautioned that this radiometric method provides only a rough distance indication. The UAP and Eiffel Tower had similar radiometric values, and motion blur lightened the object's black areas towards grey. GEIPAN therefore placed it within a broad region between the camera and Eiffel Tower, very probably nearer the camera. It considered it certain that the object was neither as distant as the La Défense towers nor within the witness's estimated 2–8 km range. Google Earth placed a reference roof 92 m from the witness. The UAP's measured angular length of approximately 0.12° would correspond to about 18.5 cm at that distance (Annex 2), but included longitudinal motion blur accentuated by the 10× zoom. Taking the blur as one-third of the total length, described by the source as a conventional assumption, gives 0.04° of blur and approximately 0.08° for the object itself. With IPACO, a great-tit-sized bird of 11–14 cm subtending 0.08° would be 80–100 m away (Annex 3), consistent with the radiometric estimate. IPACO can also estimate speed from blur angle and distance. Using 0.04° of blur at 80–100 m gave 25–32 km/h (Annex 4), which GEIPAN also considered consistent with a great tit. It classified the case B: probable photographic artefact, a bird.