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The All-domain Anomaly Resolution Office (AARO) issued this case resolution on 28 April 2025 about infrared video that a U.S. military uncrewed aerial system near Naval Air Station Sigonella recorded in December 2018 during an eruption of Mt. Etna. The operator reported a round object moving at 345 mph through the ash plume. AARO assesses with moderate confidence that the object was a balloon about one foot across, moving at about 24 mph with the wind. It found with high confidence that motion parallax caused the apparent speed and that the object never passed through the plume.
“Etna”1 page
UNCLASSIFIED (UNCLASSIFIED) (UNCLASSIFIED) Figure 3: The object at a higher magnification (0749Z) and enhanced using post-processing tools (0753Z). The object is spherical with an approximate diameter of one foot. Data Quality and Methodology: AARO assesses that the sensor data associated with the event provides sufficiently detailed information to resolve this case with moderate confidence. However, sensor limitations and atmospheric turbulence constrain the modes of rigorous analysis that can be applied to identify the object conclusively. Sensor Effects and Limitations: SWIR sensors identify targets by detecting differences in infrared energy relative to the surrounding environment. Cool objects predominantly reflect shortwave infrared energy, while hot targets predominantly emit shortwave infrared energy. These sensors do not employ active range finding, and obtaining the accurate range to a target is highly dependent on environmental factors. The thermally turbulent atmospheric conditions near an actively erupting volcano likely disrupted the sensor's ability to capture accurate data. Volcanic ash, composed of fine particulates, scatters and absorbs infrared radiation in unpredictable ways, creating a “noisy” thermal environment. These conditions further reduce the sensor’s accuracy by distorting the object’s signature. The UAS platform’s SWIR camera was optimized for air-to-ground observation rather than air- to-air detection during the encounter. In this configuration, SWIR sensors cannot detect and track airborne objects reliably and cannot provide an accurate range to the object. Airborne objects recorded by sensors configured in this way often appear indistinct, blurry, or featureless, even if they would have visually observable surface features under different collection conditions. 4 UNCLASSIFIED
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