Envelope 01

The file walks through the five-photograph Keffel sequence shot over Barra da Tijuca on May 7, 1952, captioning each frame with the observer-to-object geometry the FAB analyst reconstructed. Photograph 1 places the disc at 1,500 m with the trajectory inclined 27°30' to the horizon; photograph 5 places it at 3,000 m with a 68° disc-to-horizon inclination. The investigator notes the appearance of white and black 'sondas' (probe-like tracks) in enlargements and compares them to later Brazilian cases, including Ilha da Trindade. The follow-up survey by Colonel João Adil de Oliveira's team the next day produced photographs without sondas.