Dr. Vernon G. Plank, now at the Aerophysics Laboratory of the Air Force Cambridge Research Center, was at that time Radar Meteorologist at Walpole, Massachusetts. A specialist in the science of radar, Dr. Plank had made a detailed study of the refractive conditions prevailing over Washington for July 20 and 21, 1952. In a letter (which was never published) to the editor of True, he pointed out that the saucer theory of the Washington radar returns had no basis in fact. The material given in the letter merits quotation:
“The regular Washington radiosonde observations, when converted into refractive index terms, reveal that a very marked superrefractive condition (a condition favorable to earthward bending of radar rays) prevailed in the lower atmosphere during this period. The cause of this superrefractive condition was primarily the rapid decrease of water vapor with altitude.
“Although this superrefractive layer was not quite intense enough to cause the radar rays to be bent completely back to earth, the rays would be very markedly bent downward from their normal position. From past experience with other situations of this type it is to be expected that certain regions in this layer might be considerably more superrefractive than others, or that particular terrain features, such as rivers or small bodies of water, might create local, transitory conditions favorable to extreme superrefraction or even reflection. Another factor to consider is that whereas such local anomalies are usually due to moisture, localized temperature effects may also create or help create such intense superrefractive regions. Therefore, it would not be at all surprising that such local anomalies, when superimposed on the generally superrefractive layer already existing over Washington, could create a situation conducive to radar echoes of the type observed.
“Under such conditions the general ground clutter referred to in the Keyhoe article would not be present and the radarscope would only show echoes whenever and ‘wherever’ (qualified below) a favorable superrefractive region occurred. As the radar ray has to travel from the radar set to the particular region of refraction and thence onward to the ground, the scope echoes created by such disturbances would occur at an indicated range of roughly twice the disturbance range.
“Even slow air movements within a localized disturbance (one sufficiently intense to bend the ray into the ground) would be translated into enormous movements of the echo over the scope face. Both lateral and radial movements could be expected and disappearance of echo between sweeps would not be surprising.
“Of course, the optical effects noted in conjunction with the radar echoes would depend upon temperature effects. However, the lack of a temperature inversion in the type of data referred to by Mr. Keyhoe does not preclude the possibility that extremely sharp and localized inversions existed over the area, perhaps in close association or in conjunction with the regions causing the radar echo. The Weather Bureau data cited are not sufficiently accurate nor do the instruments used in obtaining the data have a sufficiently rapid response to measure such small inversions. Also, such data are usually obtained at only two definite periods during each day.
“As the distance between Andrews AFB and the Washington National Airport is only some few miles, the refractive effects of a given disturbance might appear to be quite similar, and the position of the resulting ground echo on the two sets might coincide to a fair degree of approximation. However, as information about the degree of accuracy maintained in plotting echo position is not available to me, I cannot comment with any degree of intelligence. It does seem though, that with the observed echo speeds and radical direction changes, as well as the echo appearance and disappearance phenomena, that accurate scope coordination between the separate fields would be extremely difficult.”[[VIII-9]]
“Simultaneous” Radar-Visual Reports
On the night of July 29, three days after the second Washington crisis, the radar installation of the Air Defense Command post near Port Huron, Michigan, had been tracking three F-94s as they made practice runs on a B-25 bomber. At 9:40 P.M. C.S.T., ground control picked up an unidentified target moving from north to south at a speed of about 625 miles an hour. The operators notified the pilot of one of the F-94s and vectored him in for an attempted intercept. The plane’s radar did not show the reported target, but when the plane had climbed to a height of 21,000 feet, both the pilot and his radar man saw a brilliant multicolored light, many times larger than a star, close to the northern horizon. At the same time the plane’s radar picked up an echo in the north; it disappeared after thirty seconds, although the light was still visible dead ahead. As the pilot began the chase, the light changed color from bluish white to reddish and slowly diminished in size as though it were moving away. The pilot pursued the light for about half an hour without gaining on it, and eventually had to return to base. The ground radar, meanwhile, had been trying to keep track of events in the sky. When the chase began, the target appearing on ground radar had first made a 180-degree turn and reversed direction from south to north; it had then moved erratically, doubling its speed instantaneously, and then slowing down. It once seemed to reach a speed of about 1400 miles an hour, then slowed to about 300 mph, and disappeared from the scope shortly after the plane had returned to base[VIII-2].
To many persons this incident seemed a simultaneous visual and radar sighting of a single unknown object but the Air Force soon demolished this theory. A study of the facts revealed that the movement of the radar target and that of the mysterious light had not coincided. The radar target had traveled from north to south, had then reversed direction, had slowed down, speeded up, and moved erratically. The light, however, had remained steadily in the north, diminishing in size and brilliance but not vanishing. It behaved, in fact, like the image of a star or a planet seen through turbulent atmosphere (see [Chapter IV]).