CESSIEU (38) 16.07.2023

On 16 July 2023 at 16:30, witnesses beside their swimming pool near their home in Cessieu (38) saw several UAPs moving slowly from south-east to north-west. T1 described a line of 4 or 5 objects, each consisting of 3 equal-sized luminous spheres and another, larger luminous sphere in the centre. Two identical UAPs nearby, outside the formation, behaved similarly. GEIPAN assesses the evidential strength as good: although only 1 account was submitted by the 2 witnesses, a video was supplied. Under its criteria, evidential strength is the quantity of information collected for an account that is considered reliable and objectively supported. The investigation found that they probably saw a cluster of decorative Mylar balloons carried aloft by a light wind (see the investigation report). GEIPAN cites the spherical shape, common in such balloons and reports; groups described in the analysis as clusters of 3, aligned or moving alongside the main group; brightness from sunlight reflected by highly reflective surfaces during sunny daytime conditions; and the initial straight, steady path consistent with windborne balloons. The source’s initial account describes 3 spheres plus a larger central sphere per object, whereas its analysis refers to clusters of 3. Météo-France’s high-resolution AROME wind data confirm compatible south-east-to-north-west winds at approximately 100–250 m altitude. Their low to very low speed matches the slow movement. AROME—Application of Research to Operations at MEsoscale—is Météo-France’s forecasting model with a very fine 1.3 km grid. GEIPAN explains each feature the witness found unusual under this hypothesis. Balloons rotating while drifting temporarily present a less reflective surface to the Sun, explaining disappearances and reappearances. Isolated UAPs suddenly moving against the formation’s overall direction are consistent with small gusts or wind shear at slightly different altitudes. This could not be demonstrated formally because the AROME data lacked sufficient resolution. For features noticed later in the video, the source attributes the witness’s disappointment at seeing less detail than with the naked eye to the smartphone’s lower resolution relative to human vision. Bright or dark points moving rapidly around the UAPs are probably video artefacts. The sighting occurred on a summer Sunday. A celebration may have taken place in the direction from which the UAPs came, but the investigation could not confirm one. Investigators were also unable to question the pilots of nearby gliders about whether they had seen the balloons. GEIPAN classifies the case A: observation of Mylar-type balloons carried by the wind.