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In Radar-Visual cases, a radar operator observes a return on his screen that is similar to that of a large aircraft, does not resemble "weather phenomena", and is not the result of malfunction. The associated visual sighting is characteristically a light, or possibly a formation of lights strikingly unfamiliar to the observer, with generally only a suggestion, if any, of an object dimly outlined by the brightness of the lights.
The speeds involved are invariably high (otherwise the radar track would be considered a conventional aircraft), but combinations of high speed at one time and hovering at another are not uncommon. Reversals of motion and sharp turns, not abrupt 90-degree turns, are characteristic of Radar-Visual cases. Nearly all Radar-Visual cases are nighttime occurrences.
There are also pure radar-only UFO incidents, with no visual confirmation of the tracked object, either because it was out of visual range or because nothing could be seen at the tracked location of the object. Hynek originally did not consider these pure radar cases to be of interest. The number of UFO reports involving radar has declined since the 1950's:
There are several reasons for this:
- The introduction of digital processing of radar signals. This processing, compared to the old analogue systems of the 1950's, 'declutters' the radar screen by removing radar returns characteristic of weather, or returns that are moving too slow or too fast to be of interest, or that are too low or too high. In the process, by definition, any objects without the speed, altitude, or radar return characteristics of conventional aircraft are eliminated.
- The use of radar transponders on aircraft. These greatly amplify the radar return, as well as encoding information as to the identity of the aircraft. Modern air traffic control in default mode is tracking transponders, not aircraft. Only in abnormal situations are 'skin paints' of objects without transponders given special attention.
- The enormous reduction in both military and civilian radar stations since the end of the Cold War. After 15 years of investment and effort, America's SAGE air defense system was completed. It consisted of 142 primary radar stations and 96 gap-filler radar sites in the United States and Canada. This radar network supported a vast defensive weapons complex, including 41 interceptor squadrons numbering 800 aircraft, seven BOMARC missile squadrons, and scores of Army Nike missile battalions stood ready (each of these also with its own surveillance and tracking radar). At this juncture Secretary of Defense Robert McNamara ordered the system to be decommissioned. By 1968 the military was operating only early-warning radar stations at the periphery of North America. By 1974 the BOMARC and Nike sites had been closed, and the remaining manned interceptors turned over to reserve units. By 1979 Air Defense was eliminated as a separate command of the USAF. The Air Force relied on FAA radars for tracking of objects within US air space. However the FAA was naturally interested only in its task of controlling commercial air traffic. By the 21st Century the number of FAA ARSR radar facilities was fewer than a hundred, each covering a radius of 200 miles. Many of these facilities could detect only transponder-equipped aircraft and were
referred to as beacon-only sites. There were numerous gaps in the net, and there was no capability to determine the altitude of an aircraft with its transponder turned off.
- The elimination of any official means of filing UFO reports since the closure of Air Force Project Blue Book in 1969. Even before this it was common management practice to discourage such reports, since all it meant was a lot of paperwork and diversion from primary duties with no result.
The combined effect of the above was clear during the 9/11 attack. The remnants of America's once enormous military and civilian radar net was not even capable of tracking hijacked airliners that had simply turned their transponders off and were not following the pre-filed flight plan. To quote from the report of the 9/11 Commission:
Controllers track airliners such as the four aircraft hijacked on 9/11 primarily by watching the data from a signal emitted by each aircraft’s transponder equipment. Those four planes, like all aircraft traveling above 10,000 feet, were required to emit a unique transponder signal while in flight.
On 9/11, the terrorists turned off the transponders on three of the four hijacked aircraft. With its transponder off, it is possible, though more difficult, to track an aircraft by its primary radar returns. But unlike transponder data, primary radar returns do not show the aircraft’s identity and altitude. Controllers at centers rely so heavily on transponder signals that they usually do not display primary radar returns on their radar scopes.
Despite all of these factors, UFO reports involving radar, which ran at 5% in the 1950's, have remained fairly constant at between 1% and 2% of all UFO sightings since the late 1960's.
Of course, since the heyday of the UFO and the last official studies, stealth technology has been revealed and developed. Whereas radar tracking was then seen as 'proof' of the existence of an unidentified aerial object, it now would be considered unremarkable if a visible object was invisible to radar - since earthly technology has been able to accomplish that since the 1970's… Radar-Visual UFO reports Chronology Radar-Visual UFO reports by Location
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