Part 14

Radar only reports. It does not interpret. If the sweep hand on successive rotations shows a spot of light apparently moving from position _A_ to position _B_, to _C_, to _D_, the operator generally concludes that the blips represent a single object that is moving at a certain speed in a certain direction (see Figure 13). If successive sweeps show a spot of light that remains at position _A_, he usually concludes that it represents a stationary object. If the blip moves a very great distance in the interval between two sweeps or seems to jump erratically from one position to another, an amateur might interpret it as a spacecraft flying at incredible velocity--a flying saucer. But an expert would probably conclude, especially under certain weather conditions, that the scope was picking up echoes from two or more separate objects, one reflecting briefly at position _A_, another at position _B_, and so on.

_The Principle of Radar_

Radar is an electronic assembly far too complex for detailed description here, but its basic principle is simple. It is merely an echo machine that reflects radio waves instead of sound waves. To illustrate by a rough analogy, let us imagine that a man is standing in the middle of an open field on a very dark night. He wants to find out something of the contours of the surrounding country but his only tools are a compass, a watch with luminous dial and hands, and a large megaphone. He raises the megaphone to his lips, points it directly north, and gives a sharp and piercing call: “Hi!” He now cups his hand to his ear and listens for an echo. Hearing no reply, he deduces that in the north there are no hills, tall buildings, or other obstructions that might have produced an echo.

Changing his position, he turns to the east and tries the experiment 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_