Puerto Rico Case Resolution

UNCLASSIFIED
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UNCLASSIFIED
Data Quality and Methodology
AARO assesses that the sensor data associated with the encounter provides sufficiently detailed
information to resolve this case with high confidence. AARO’s assessment is informed by
reconstruction of the event using STK and Minimum Separation Vectors analysis.
Sensor Effects and Limitations
Thermal imaging can fail to differentiate a target object from the background when its thermal
signature is virtually identical to the surrounding environment to be distinct, known as thermal
crossover. When a sensor fails to discriminate a target from its environment, the object can seem
to vanish or intermittently disappear and reappear.3 Several factors affected the objects’ IR
signature, contributing to the perception that they entered the water or disappeared.
• Thermal Crossover:
This natural phenomenon reduces the effectiveness of thermal imaging systems in
detecting the contrast between an object and its environment during and after a rapid
temperature change, such as during sunrise and sunset. It can persist for up to two
hours.4
On April 26, 2013, sunset occurred at 7:48 p.m. local time. The IR sensor recorded
the event at 9:22 p.m. local time, within the two-hour window when thermal
crossover can influence IR sensor return.5
• Sensor Distance:
The aircraft’s distance from the objects nearly tripled during the observation period.
Sensor fidelity degrades with increasing distance to a target, especially for objects of
such small size.
• Cloud Cover:
Scattered clouds at 3,000 feet partially obscured the sensor's view. Cloud cover can
intermittently reduce an object’s thermal contrast, similar to the loss of detection that
can occur during thermal crossover.6 Intermittent sensor contact can make an object
appear to flicker or disappear and reappear on thermal imaging systems.
Alternative Hypotheses
Anomalous Phenomena: During specific frames, the objects seem to pass behind a utility pole,
indicating that they were at a much lower altitude and traveling much faster than would be
typical for objects of this size. AARO employed pixel analysis to investigate this alternative and
found that the objects did not pass behind the pole, ruling out anomalous performance
characteristics. Pixel analysis alone cannot determine the objects’ altitude or trajectory, though it
can set parameters for further analysis. Therefore, AARO used STK reconstruction to assess the
objects' flight behavior and performance characteristics. The STK reconstruction demonstrates
that the objects moved in a straight line at wind speed over land.
Marine Birds: An AARO partner assessed that the objects traveled between 35 and 130 mph at
an altitude between 300 and 900 feet. The partner suggested that the objects were a pair of
marine birds that descended to the surface of the Atlantic Ocean but noted that poor data quality