again. After an interval his call returns as a faint echo: “Hi!” The
time elapsed between call and echo, according to his watch, is ten
seconds. His call has taken five seconds to reach the object and five
seconds more to return. Since he knows that sound travels at the rate
of about 1000 feet a second, he deduces that an obstruction lies in
the east, about 5000 feet away. Slowly changing position, he repeats
his call at various points around the compass. Some echoes take longer
to return than others, indicating more distant objects. Other echoes
come back in a fraction of a second, showing an object very close. Thus
he gradually constructs a mental map of the surrounding terrain.
Radar detects and locates objects in a similar way, by reflecting sharp
pulses of radio waves. But spurious echoes, which sometimes deceive the
operator, can also appear on the scope. These “anomalous” or abnormal
returns may have one of several causes, including the nature of the
radar mechanism itself. To help explain this, let us go back to our
analogy of the man in the open field. Let us suppose that the man has
mechanized his device. To ease the strain on his vocal cords, he has
built a megaphone with a record-playing device. The megaphone rotates
automatically and sends out a recorded “Hi!” once every twenty seconds,
as regular as clockwork. To increase the sensitivity of his hearing, he
wears ear trumpets that point in the same direction as the megaphone.
This procedure is more effective than cupping his ears and eliminates
some of the extraneous noise that might come in from the rear and the
sides.
With this improved equipment the man now repeats his experiment. As
before, he gets no signal from the north. When he turns to the east
he gets an echo after ten seconds, just as he did during his first
experiment. As he continues to turn slowly, like a minute hand on a
clock dial, he mentally maps the positions of the echoes as distances
along the hand from the center of the dial, and compares this new map
with the crude one he constructed earlier. Basically the two agree.
But wait! From the southwest he hears a new echo that did not occur
in his earlier experiment. It returns after two seconds and thus
apparently comes from an obstruction 1000 feet away. Puzzled, the man
decides to walk toward the object and check his observation. After he
has covered half the distance he stops, sends out a call, and listens
for the echo. The indicated distance to the echo-producing object is
now 500 feet, just as he calculated. And so he goes on, checking at
intervals. When he has covered 990 feet he knows that he should reach
the obstruction at any moment and to avoid colliding with it in the
darkness he proceeds with extreme caution--995, 996, 997, 998, 999
feet. He puts out his hand, expecting to touch a building or a stone
wall, and warily takes the last step. But he finds no structure of
any kind, merely level ground. And at the same moment he finds to
his astonishment that he can no longer detect the echoes he had been
following. What has happened? Has his equipment been malfunctioning?
Or was the unknown structure perhaps a vehicle from outer space that
waited until he was practically touching it and then rose silently in
an enormous burst of speed and vanished?
The man checks and finds that his equipment is functioning perfectly,
since he can still pick up echoes from the terrain he had mapped
earlier. He then walks back ten feet and listens once more for an
echo from the phantom structure. Again he gets a signal, apparently
from an obstruction just ten feet ahead. Has the mysterious object
suddenly returned? But how could it have done so without disturbing
the atmosphere or making a noise? By this time our man is frightened
as well as puzzled, but he boldly decides to make one more experiment.
He walks again to the point where the obstruction should be. Signaling
again to the southwest, he now gets a faint echo apparently from a
distance of 10,000 feet. Tired as he is, he starts walking toward this
new obstruction and eventually reaches his goal. He now finds the
true source of the returns--a high hill that rises abruptly from the
plain. The hill is 10,000 feet away from the position indicated by the
original series of echoes, and 11,000 feet away from the place he stood
when he first sent out the signals.
Finally the man figures out the explanation. When he made his first
experiment, with primitive equipment, he had given one sharp shout
and then waited for a long time for the signal to return; thus there
was never any uncertainty about the source of the echo. The time that
elapsed between shout and return had clearly indicated the distance of
the echo-producing object. But the improved automatic equipment of the
second experiment produced a train of signals going out continuously
at regular intervals, twenty seconds apart. Therefore when the sound
waves encountered a definite object, a train of echoes began coming
back, twenty seconds apart. An object at a distance of 10,000 feet
would return an echo in twenty seconds; another object at a distance
of 11,000 feet would return an echo in twenty-two seconds. But an
echo from this second object would reach the listener at exactly
the same time as an echo from an object only 1000 feet away. He now
understands why he seemed to detect a structure at a distance of 1000
feet which disappeared as he approached and then reappeared 10,000 feet
farther away. In fact, the object that returned the misinterpreted
echo could have been 20,000 or 30,000 or 40,000 feet farther away--any
multiple of 10,000 feet. Large numbers of signals were returning every
twenty seconds. The man had no way of deciding for certain whether
a particular echo came from the most recent signal and therefore
indicated a relatively close object, or whether it came from an earlier
signal and therefore from a more distant object.
Broadening his experiment our man eventually learned other
characteristics of these echoes. He found that on the average day he
was rarely plagued by this uncertainty in identifying the returns. The
second-round echoes were very weak, almost undetectable, and therefore
caused no major problem. But on other days, under different weather
conditions, sound tended to travel long distances without losing much
in intensity. On such days the echoes were often confusing.
_Weather and Radar Echoes_
Radar is an echo machine that reflects radio waves instead of sound
waves. Instead of traveling at the speed of sound, about 1000 feet a
second, radio waves travel at the velocity of light, 186,000 miles a
second. Successive pulses go out at very short intervals, perhaps one
one-thousandth of a second apart, so that each pulse is followed by
another just 186 miles behind it. If the operator gets a return from an
object that is apparently at a distance of 25 miles, he must sometimes
allow for the possibility that he is getting a secondary echo and that
the actual distance may be different. The object that produces the echo
may be at a distance of 25 plus 186 miles, or 25 plus twice 186 miles,
or 25 plus any other whole-number multiple of 186 miles.
Under ordinary circumstances, the reflections from very distant targets
rarely confuse the operator. The curvature of the earth tends to shield
the radiation, and the distance factor alone reduces the intensity to
a negligible value. But weather can cause peculiar returns. A layer
of warm air above cooler air at the earth’s surface has much the
same effect on radio waves that it has on light waves. A temperature
inversion can produce radar “mirages”--commonly called “phantoms,”
“ghosts,” or “angels.” Relatively small amounts of warm air, even mere
warm bubbles in a layer of colder air, will suffice. When the scope
records a series of blips, the operator ordinarily assumes that all are
returns from a single object. If inversions of temperature or humidity
exist in the atmosphere, however, the series of returns may represent
several different ground objects rather than a single object in the
sky. Since these inversion layers do not remain fixed but move, change,
and shimmer, on one sweep the radar may reflect one ground object and
on the next sweep some fifteen seconds later may reflect a totally
different ground object five or six miles away from the first. An
inexperienced operator might conclude, wrongly, that both echoes came
from a single object that had traveled five miles in a fraction of a
minute (see Figure 14). Similar mistakes in identity have caused many
reports of radar flying saucers.
[Illustration: _Figure 14._ Deflection of radar beams by temperature
inversion. Top, radar picks up ground target. Bottom, on next sweep,
radar picks up different ground target, which seems to indicate a
fast-moving UFO.]
Such a radar incident occurred at one of our defense installations
in Alaska early in the morning of January 22, 1952[VIII-2]. Shortly
after midnight a bright target appeared on the radarscope, moving down
from the northeast, fairly high, and apparently traveling at about
1500 miles an hour. Unidentified targets require particularly prompt
investigation in this sensitive area so close to Siberia. Within
minutes an F-94 jet was moving in from a fighter base 100 miles to
the south; two other jets were scrambled at intervals and vectored
in toward the unknown target by ground radar. When radar switched to
short range, however, it always lost both the target and the pursuit
plane, even though both were close to the radar site. The first jet
could find nothing in the air, and no echoes appeared on its radar.
The second jet saw nothing in the air, but its radar recorded a
brief, weak echo to the right at about 28,000 feet. The echo faded
immediately, returned briefly, and then disappeared as the jet closed
in. The third jet, after cruising the area for ten minutes without
detecting anything visually or on radar, suddenly got a strong radar
return from an apparently stationary target just as it passed over the
ground radar site. The pilot made three direct runs on the unknown.
Each time he broke off the intercept when he got within 200 yards of
the target position as shown on his radar, for fear of collision. At no
time did he see anything at the supposed location of the target. (This
experience is somewhat analogous to that of our man who used echoing
sound waves to locate a solid structure only to find, on reaching the
indicated spot, that the structure was not there.)
Captain Roy James, chief of the radar section of ATIC, examined all the
data and the scanty weather reports then available for this Alaskan
area, and concluded that the targets were ghost returns probably
from the ground, caused by peculiar atmospheric conditions--the same
conditions that had interfered with normal operation of the ground
radar. Although ground structures are scarce in that part of Alaska,
they do exist, and so do mountains. The analysis was undoubtedly
correct, even though knowledge of the location and movement of the
temperature inversion was too imprecise for the analyst to plot and
locate the true target that produced the reflections[VIII-3, p. 167].
Some of the nation’s most brilliant physicists have carried out
fundamental research into the behavior of microwaves under varying
conditions. The technical nature of these investigations makes them
difficult to describe in ordinary language, but they provide vital
information for the expert.
One such study has specifically attacked the problem of radar images
that perform rapid and erratic maneuvers at close range and seem to
overtake, fly parallel with, or almost collide with the pursuing
aircraft. Such returns may be caused by the “non-isotropic secondary
scattering of energy” (that is, the radio waves are not reflected in
a uniform manner) from an airplane to a ground object, or from ground
object to plane. Under appropriate weather conditions the plane itself
causes the puzzling echoes, so that the velocity and movement of the
radar “saucer” depend directly on those of the plane. When the aircraft
is the first of the two scatterers, the radar saucer always appears
at the same bearing as the plane, and is always farther away from the
detecting radar than is the plane. Thus the path of the phantom always
lies outside the path of the aircraft, and when the jet performs a
360-degree turn, the phantom also turns, on an outside path. However,
if the jet happens to fly directly over the ground object that is
reflecting the energy, then the observing radar will see the images of
the jet and the phantom flying on what seems to be a collision course.
Conversely, when the ground object is the first of the two scatterers,
the saucer phantom always occurs at the same bearing as the ground
object, and the distance to the phantom is always greater than to the
ground object. If the aircraft crosses the radial line from radar to
ground object, at a range exceeding the range to the object, then the
echoes from plane and saucer almost merge at the point of crossing, in
a “near collision.” But if the plane flies “this side” of the object,
then the plane and saucer will never be closer together than the
distance between plane and ground object at the point of crossing. A
height-finding radar, trained on the pursuing plane, would show the
phantom saucer apparently diving toward or climbing away from the
plane, attacking and retreating at very high velocities[VIII-4].
_The Kinross Case_
Some such mechanism probably explains the radar returns reported in the
Kinross case, which some saucer publications cite as a proved instance
in which a flying saucer attacked a plane. On the night of November
23, 1953, an Air Force jet was scrambled from Kinross Air Force Base,
Michigan, to intercept an unidentified plane observed on radar. The
jet successfully accomplished its mission and identified the unknown
as a Dakota, a Canadian C-47. On its return to the base, however, the
Air Force jet crashed into Lake Michigan and, as often happens when a
plane crashes into deep water and the exact place of the crash is not
known, no wreckage was ever found. As the ground radar at Kinross had
tracked the returning jet, the scope had picked up a phantom echo in
the neighborhood of the jet; the two blips had seemed to merge just as
both went off the scope.
Since the crash was not reported as a UFO incident and did not involve
any question of unidentified flying objects, ATIC was not asked to
investigate the problem. The office of the Deputy Inspector General for
Safety carried out a thorough inquiry and concluded that the crash had
been an aircraft accident, probably caused by the pilot’s suffering
an attack of vertigo. As for the two blips shown by radar, the night
had been a stormy one and atmospheric conditions had been conducive
to abnormal returns. The phantom echo had almost certainly been a
secondary reflection produced by the jet itself, and it thus merged
with the return from the jet and vanished with it when the plane hit
the water.
Solely on the basis of this radar phantom, some civilian saucer groups
have tried to transform the Kinross crash into a UFO mystery with Air
Force investigators as the villains, and have suggested that the ghost
blip represented an alien spacecraft that happened to be cruising over
Lake Michigan that night and attacked the jet for one of two reasons:
1) The saucer might have tried to avoid close contact with the jet by
employing a “reversed G-field beam” (see _Chapter_ IX); colliding with
this beam as with a stone wall, the jet crashed. 2) The saucer might
have used the G-field to scoop the plane out of the air and take it
aboard the spacecraft; the captured pilot might have been needed to
teach the English language to his alien captors.
_The “Invasion” of Washington, D.C._
The most famous of the radar phantoms are those that “invaded”
Washington, D.C., on the nights of July 19 and July 26, 1952, and
terrified a large number of radar operators, pilots, and Air Force
officials who in a more normal emotional climate would have recognized
the “invisible” flying saucers for what they were--radar angels
produced by weather conditions[VIII-2]. All during July the eastern
seaboard had suffered an unprecedented drought and heat wave. Lack of
cloud cover produced intensely hot days and rapid radiative cooling
of the earth’s surface at night. This situation, combined with the
prevailing light winds, was ideal for the formation of low-level
temperature inversions during the hours of darkness[VIII-5].
The hundreds of flying saucers reported during the summer (_Chapter_
VII) had produced a state of near-panic which entered its acute phase
on July 19, at 11:40 P.M. E.D.S.T., when a group of seven unidentified
targets appeared on the radarscope of the Air Route Traffic Control
(ARTC) at the Washington National Airport[VIII-3, p. 209 ff.]. Similar
targets that moved erratically, appearing and disappearing, were
observed on the radars of the control tower and of nearby Andrews Air
Force Base. If the blips were to be accepted at face value, then a
host of aerial objects had invaded Washington and were cruising over
the White House and the Capitol. Traffic control notified the pilots
of commercial flights in the area to keep alert for unidentified
aircraft. Some pilots reported unusual echoes on their plane radars,
some reported only normal returns, and two pilots reported unexplained
lights in the neighborhood indicated by radar. Nobody saw any strange
aircraft. After several requests from ARTC (which unaccountably did not
notify officials in the Air Force Intelligence that an “invasion” was
taking place), a jet interceptor finally arrived about dawn to search
the area but found nothing. Meanwhile the targets had vanished from the
radarscopes.
Next day the report flashed all over the world that a fleet of flying
saucers had invaded Washington, and public tension became almost
tangible. Was the earth doomed? The terror reached its climax on July
26, just a week after the first incident, when at 10:30 P.M., E.D.S.T.,
the same radar operators who had observed the first “invasion” picked
up another group of mysterious blips on their screens. The host of
unknowns had apparently formed a ring around the city of Washington and
the surrounding countryside. This time Air Force Intelligence officers
were notified. They raced to the airport to see the radarscopes for
themselves, and concluded that real saucers must be in the sky. All
commercial air traffic was then diverted from Washington, reporters
and photographers were barred from the radar room, and Air Force jets
took to the air to defend the nation. But against what? The enemy, if
there, was invisible. One pilot saw a bright light that vanished when
he began to chase it; later, his radar showed a return that faded after
a few seconds, but he could not find a visual target. In the hours
between midnight and dawn, jet interceptors scoured the skies looking
for mysterious objects that produced returns on ground radar but not on
plane radar, and were invisible to the human eye. They found nothing.
One pilot who flew this mission, accompanied by a copilot who was also
a radar officer, later described his experience:
“For a period of 1½ hours the B-25 was vectored at altitudes varying
from 1,000 to 4,000 feet MSL to the objects observed on the [ground
radar] screen. The airplane flew circles around stationary blips, flew
through and along with their formations, paralleled their flight, and
was observed in the radar screen to pass directly over, under, or
through an angel. At all times the echo return of the aircraft caused a
brighter return on the screen than the angel. The radar height finder
was not operating during this mission, so exact altitudes of the blips
could not be determined.
“No unidentified objects were observed by me or the crew during the
flight. At 2300 E.D.S.T. all angels disappeared from the radar screen
and screen detection returned to normal.”[VIII-6]
By dawn this fantastic war of the angels had ended and the post-mortems
had begun. One radar expert who kept his head in spite of the hysteria
was Captain Roy James of ATIC, who immediately recognized the targets
as caused by weather. A civilian expert on radio propagation, when
consulted, correctly identified the phantoms and explained how they
were produced[VIII-7, VIII-7a]. General Samford, then in charge
of the UFO investigation, concurred. But most newspapers and many
government officials, influenced by the general excitement, ignored the
conclusions of the experts. Saucer enthusiasts regarded the phenomena
as a real invasion from space, and alleged that the Air Force was
covering up the truth.
Weeks passed before the facts of the incidents could be separated from
the fancies. Three ground radars had observed unusual targets on the
nights of the “invasion.” Only once, however, did all three observe
what was apparently the same target, and that for a few seconds only.
The unusual radar echoes had no visual counterpart--nobody had seen
or heard a spaceship. A few pilots had reported unidentified lights,
but the Washington area at night displays thousands of lights, and
even an unexplained light is far from being a spaceship. One pilot who
took part in this phantom war reported that, again and again, ground
radar had vectored him in toward a target that proved to be a steamboat
making a moonlight trip on the Potomac!
_Radar Experiments in Washington_
Immediately after the Washington crisis, the Technical Development and
Evaluation Center of the Civil Aeronautics Authority was assigned the
problem of finding out exactly what had produced the radar returns.
Investigation showed that the phantoms were not a new or unusual
phenomenon. They had appeared on the Washington radars on many nights
before the first “invasion,” appeared twice during the week between
the two, and many times after the second. Abnormal returns are
commonplace during the hot summer months when temperature inversions
and inequalities in the moisture of the air are most frequent. On the
nights of July 19 and 26 the Weather Bureau at Washington recorded
small temperature inversions and an abnormal distribution of moisture
in the atmosphere, conditions that regularly produce radar angels.
The experts also carried out a series of experiments in the Washington
area on several nights in August when conditions of temperature and
humidity closely resembled those on the “invasion” nights. During
these experiments unidentified targets appeared in profusion on the
radar screens. The first observation period began on the evening of
August 13, 1952. At about 9 P.M. E.D.S.T., suddenly “a group of seven
strong stationary targets became visible in an area about fifteen miles
north-northeast of the radar antenna. During the next two or three
antenna revolutions, the area on the scope between Washington and
Baltimore became heavily sprinkled with stationary targets in a belt
about six miles wide. A group of additional targets became visible in
an area approximately ten to fifteen miles south of the radar antenna.
This was evidence of the beginning of a temperature inversion.”[VIII-6]
Two temperature inversions were involved, one just above the earth’s
surface, and one at about 8000 feet. The investigators concluded that
the unidentified targets observed on Washington MEW (Microwave Early
Warning) and other radar in the summer of 1952 were to be attributed
to secondary reflections of the radar beam, caused primarily by
temperature inversions[VIII-5].
Saucer enthusiasts protested (and still insist) that the inversions
were not large enough to produce radar anomalies, revealing how
superficial was their acquaintance with radar. Although pronounced
temperature inversions are responsible for the superior and inferior
mirages resulting from the bending of light rays, large inversions
are not required to produce the mirages resulting from the refractive
bending of radio waves. At radar frequencies, refraction is influenced
by both temperature differences and the distribution of water vapor
in the atmosphere. A pronounced drop in moisture content at higher
altitudes can easily cause radar rays to bend earthward and pick
up ground targets, even though temperature conditions in the lower
atmosphere are entirely normal.