Analysis of Radar and Air-Visual UFO Observations
on 24 October 1968 at Minot AFB,
North Dakota, USA
2.1. Description of the B-52 Radarscope Photographs
Generally, I agree with Shough’s expert analysis of the B-52 radar system (ASQ-38), and interpretation of the photos. Accordingly, I will concentrate on my own independent analysis of the sequence of 14 radarscope photos (771-784) filmed onboard the B-52.
At the time of the UFO events, the radar navigator switched the radar system to “Station-keeping” mode, whereby the radar coverage is elevated and concentrated close to the aircraft. In this mode, the Plan Position Indicator, or radarscope display, draws a concentric map that has as its center the position of the aircraft, oriented according to its heading. In this instance, the right edge of the screen is a bit askew, possibly due to the fact that photographs were acquired from the back of the cathode-ray tube by means of prisms and lenses, which does not permit an axial photo of the screen image. However, the deformation caused by the oblique view is well corrected. The photograph is exposed for a time exposure of three seconds, which corresponds to one complete rotation of the radarscope’s radial sweep. The sweep is synchronous with the rotation of the radar antenna located beneath the nose of the B-52. The technical manual for the radar indicates that the rotation is clockwise, which is confirmed by the progressive increase of brightness of the ground echo. The radial sweep is visible by the inclined radial line at 284 degrees, which is the point where the camera shutter briefly closes during the next film frame advance. Because the radar screen contains phosphorus with a long persistence, the beginning of the rotation is more intense due to its extended exposure.
The photo is exposed on 35mm black and white negative film, which was developed after the flight and subsequently interpreted by an intelligence officer. Aside from the clock, informational data plate, and frame counter, these photos contain specific information including the heading of the aircraft, and the distance and azimuth of the radar echoes. The radarscope is calibrated for distance by visible concentric circles (i.e., range markers) at 0.75, 1.25, and 1.75 nm from the center, and to a five nm circumference at the outer edge. We can also calculate the specific altitude of the B-52 at the time of photo in relation to the altitude hole, which decreases in diameter as the B-52 descends in altitude.
The heading of the aircraft is towards the top of the photo, so what we see on the scope is the actual orientation of the echoes in relation to the aircraft. The heading at the top appears to be 118 degrees, however, there are two visible lines that extend out from the center in the direction of the flight. Extending the left line determines a course of 122 degrees, whereas the right line corresponds to a marker at 132 degrees. This is a bit confusing, and the lines and concentric range markers are not always visible in the photos, particularly in the dark zone of the ground (terrain) echo, since the contrast is hidden in the noise. It is not clear if the B-52 heading indicated on the photos (122 or 132 degrees) is the true geographical heading or the magnetic heading, but it appears that 122 degrees corresponds to the magnetic orientation of the runway.
The B-52s at Minot AFB were specially equipped for navigation over the northern Polar Region, where the use of magnetic navigation is useless, since the headings change continuously when the magnetic field of the Earth is practically vertical. Therefore, means of inertial navigation incorporating gyroscopes were used for accurate navigation over the Polar Regions. In principle, these systems give true course. It seems plausible that the bombing radar would be adjusted to the inertial navigation system, making the 132-degree heading the true course.
The same day of the incident, 5th Bombardment Wing, intelligence officer Staff Sgt. Richard Clark analyzed the radarscope film at the request of his superiors. Clark ordered two sets of 20 X 25 cm (8 X 10 inch) photographic prints of the 14 frames from the original 35mm negative. He included one of the sets of prints with his report and kept the second set as a file copy. Years later, Clark gave the second set of photos to his brother-in-law, William McNeff, a representative of the Mutual UFO Network (MUFON) for the state of Minnesota (a private organization involved in the study of the UFO phenomenon). It was by chance that Tulien, also a resident of Minnesota, was informed of the existence of these original photos, which McNeff generously provided for analysis. In sum, the radarscope photos are first-generation photographic prints from the original 1968 film-negative.
The photographs were sent to me as digital files with a resolution of 300 pixels per inch (on average 150 pixels per nm). This allowed for repetitive distance measurements with accuracy in the order of 12 meters. According to the technical documentation, the radar has a resolution of 37 meters; so we have a resolution of the photos that is three times that of the radar. Further, I obtained extracts of the photos from Tulien with an increased resolution of 800 dpi. Following are close-ups of the successive radarscope photos indicating the various radar echoes that appear within the altitude hole.
To underscore the importance of these photographs, all successive echoes are inside the central zone referred to as the altitude hole, and therefore can only correspond to airborne targets. In addition, the B-52 speed was on average 460 km / h (285 mph), so that the radar target would have to maintain the same velocity in order to remain in the altitude hole (and high-acceleration when it changed position).
The position of the target is in fact an instantaneous relative position that is imaged at the precise instant when the radar beam swept the target. This occurs at very high speeds. For example, at the 1.75 nm range ring the sweeping speed of the beam would be in the order of 24435 km / h (15190 mph). We should also consider the size of the target that was identified by the radar beam. According to the radar operator, the size of the echo was larger than a KC-135 Stratotanker (41 x 39 meters) and therefore the target could not have been an aircraft. For example, the size of the radar echo in Figure 16 measures in the order of 280 x 140 meters, compared to the size of the B-52 measuring 48 x 56 meters. Taken together, we know of no human device this size that can fly at the measured speed. In most of the photos the intensity of the echo is considerable, and nearly at the same level as the echo of the ground below the B-52. The UFO echo also contains some photometric structure (i.e., limb to center radar albedo increase), which further confirms that this echo could not have been an artifact.
Figures 15 and 16 show that within 3 seconds, the echo made an abrupt turn and moved from the aft right to the left of the B-52, traveling 2.09 nm (3.9 km) at an apparent speed of 4600 km/h (2858 mph). The largest dimension of the echo is oriented approximately at right angles to the heading of the B-52. Figures 15 and 16 also show the echo oriented as though the UFO has traveled in the direction of the echo’s largest dimension.
In photo 774 the echo has vanished. There are several possibilities for this disappearance. Either the UFO was out of the field-of-view of the radar below the aircraft, which covers only about 50 degrees in the vertical plane resulting in a blind conical zone under the B-52, or the UFO exceeded the altitude of the B-52, or was possibly beyond the edge of the altitude hole and drowned in the considerable intensity of the ground echo.
The echo that recurs roughly one nautical mile to the left of the B-52 at ~40 degrees, is the only echo that consistently appears in the same place in eight of the photographs. This location of the UFO is also consistent with the documentary evidence, and the testimonies of the B-52 Navigator and Co-pilot. Nevertheless, this does not exclude the possibility that more than one UFO briefly accompanied the B-52.
Compare the diameter of the altitude hole in 782 with the earlier photos. In this instance, the 1.75 nm distance range ring now appears near the edge of the altitude hole, confirming the descent in altitude of the B-52. Following this, the radar echo abruptly disappeared from the radarscope. At this time, the B-52 was approximately 18-19 nm from the TACAN (located adjacent to the runway), at about 9000 feet MSL, and just emerging under the overcast. The Base Operations Dispatcher directed the security and maintenance personnel at the November-7 Launch Facility to the time and location of the incoming B-52. The N-7 personnel observed and clearly heard the B-52 high in the west, but did not observe the UFO that had been closely pacing the aircraft. At about the same time, the UFO they had been observing southeast of N-7 also disappeared from view.
In the course of photo 784, the radar operator apparently switched the radar mode to sector scan (bombing assessment mode), attempting to look towards the rear of the B-52. At this time, the B-52 was approximately five minutes out from the Minot runway, intending to land after completion of a low and missed approach to the runway, and one final circuit around the traffic pattern.
The radarscope is calibrated for distance by the concentric circles (range rings), which are located 0.75, 1.25, and 1.75 nm from the position of the B-52 at the center of the scope. These are designated in the technical training manual for the radar, and confirmed by an engineer who was responsible for the maintenance of these radars in the early 1970s. (The distances have been further verified by testing their consistency with another set of possible distances corresponding to 0.5, 1.0, and 1.5 nm). I have taken careful measurements of all of the photographs, but since a long list of numbers would be of little interest to most readers they are presented in Appendix 2 for reference.
The photographs display an informational data plate identifying the aircraft, radar operators and date of the mission. The photos also show an echo with the classic characteristics of a UFO, and depict a descending flight pattern that is consistent with a B-52. Furthermore, the positions, altitude, and speeds are also consistent, while supported by information in the documents and the witness accounts. Since the atmosphere is rarely calm and piloting seldom perfect, one would normally expect to find small, distinctive fluctuations in the heading of the B-52. In order to examine this conjecture, the top of the calibrated circle (heading indicator) on each of the radarscope photographs was measured with the accuracy of one pixel. Following are the results:
The average value is 117.9 degrees (776), and the variances have been calculated in reference to this average. We can observe that the course heading changes continuously, and that a period of variation occurs in the order of 5 photos, or for an average period of 15 seconds. The performance of a swept-wing aircraft the size of a B-52 is typically affected by aeroelastic and pitch-roll coupling effects, which result in a dynamic oscillation known as Dutch Roll. The amplitude and period observed here are quite characteristic of this type of swing. Furthermore, the heading indicated in the photographs matches the trajectory from the WT fix to the runway at Minot AFB. Therefore, these photographs are true radarscope photographs taken onboard an aircraft having the characteristics of a B-52.
There appear to be several UFO echoes of variable sizes in photos 771, 776, 777, and possibly in 781. These echoes seem too broad and intense to be simply instrument noise, ground terrain, or weather-related artifacts, and they do not appear in subsequent photos. In any case, it is possible that there was more than one UFO near the B-52.
Numerous ground witnesses at various locations reported observations of two similar UFOs, and we also know that ground personnel from their position at N-7 were observing a UFO in the southeast, during the same period of time that a UFO was pacing the B-52 at altitude in the northwest.
If a UFO close to the B-52 had moved away to a distance beyond the radius of the altitude hole, the echo would be drowned in the saturated radar return of the ground, and we would most likely not be able to see it on the radarscope. Furthermore, the radar could not detect anything beneath the aircraft within the blind cone of the 111.6-degree summit angle. Be that as it may, the available data do not allow us to determine whether more than one UFO was present.
Each radarscope photograph is a 3-second time exposure synchronized to one clock-wise rotation (360°) of the radar antenna. The photographs include a clock, in which the second hand is not blurred. This indicates that the clock has been photographed as a snapshot, via a separate optical path and superimposed onto the film. The thin line extending to about 284o indicates the camera shutter closing briefly at the point of film advance, which begins each 3-second exposure.
If the echo does not change position in successive photos, then the time interval between the consecutive imaging of the echo is equal to the period of rotation of the radar antenna, or three seconds. If the echo does change position in successive photos, then the time interval between the consecutive imaging of the echo will be +/- three seconds, depending on its change of position in relation to the beam sweep. This is particularly the case for the transitions between photos listed in Table 2.
In the following table we have accurately measured the length and width of the echoes in eleven photos, including the degree of orientation, which is the angle of the long axis of the echo in relation to the heading of the B-52. We can establish the following table for the most important echoes:
The average of the 11 values, without considering the filaments or growths of the echo on certain photos is:
- Average length = 157 meters
- Average width = 62 meters
However, the resolution of the radar in distance is 30 meters. This means that the edges of a target have an uncertainty of position in the order of +/- 15 meters. A target 30 meters real-width would be painted on the radarscope as an echo 60 meters wide with blurred edges. As a result, we must reduce the dimensions from the previous average values to the resolution of the radar. We then have:
- Corrected average length = 127 meters
- Corrected Average width = 32 meters
Another interesting result is obtained by comparing the intensity of the UFO echoes with the intensity of the returned radar signal of the neighboring ground (Sol).
In Table 4 we see an intriguing variation of the echo intensity when the UFO is at a constant distance of 1.05 nm from the B-52. Neither the distance nor the relative positions of the UFO echo vary in these photos, although the intensity of the radar signal varies considerably from 89% to 56% in pixel saturation. In contrast, the pixel saturation of the most intense ground signal varies less between photos from 91% to 78%. This variation would appear to rule out the possibility of an absorbing cloudy layer interposed between the echo (target) and the radar antenna to explain the variation in the intensity of the UFO echo, since the ground echo-level would also vary accordingly. Consequently, there is an attenuation of the returned radar signal due to other factors.
One possibility is an attenuation of the transmitted and received signal as a result of the parabolic properties of the radar antenna. This antenna has a narrow radiance diagram in the horizontal plane (in azimuth), in order to acquire a precise angular resolution of a target’s position, but in the vertical plane the radiance diagram has a particular shape.
Let us assume for now that the antenna is not tilted either up or down. The radar antenna of the B-52 has a diagram of theoretical radiance that is calculated according to the angle Alpha, existing between the nadir (the vertical point directly below the aircraft) and the direction of the target. The law of variation of the received power is in Cosecant Square of Alpha. This means that the relation between the power emitted in the direction of the axis of the antenna (“AVANT” in Figure 28) and the received power from the direction of the target is the following:
- Power received in direction Alpha = Cte . Power emitted in direction 90° . [1 / sin2 (Alpha)].
The attenuation is of a factor 132 for an angle Alpha = 5 degrees (21 decibels or dB), and of 4.5 times for Alpha = 28 degrees (6.6 dB), etc. There is an attenuation 1 / sin (Alpha) in the emission of the radar pulse, and the same attenuation in the returned pulse resulting in a total pulse attenuation varying as [1 / sin2 (Alpha)]. This effect is simply due to the geometric projection of the radiant surface of the antenna parabola in the direction of the target. This type of antenna design effectively diminishes the attenuation of a ground echo situated directly below the B-52 and increasingly distant from the vertical. This design thus compensates the natural attenuation caused by distance, which varies as the fourth power of the distance for radar receiving a natural echo. Moreover, the ground absorbs the radar wave to some degree and returns only a part of the radar signal towards the aircraft.
The same effect would apply to the UFO accompanying the B-52. However, we cannot infer the location of the UFO in comparison to the horizontal plane of the B-52. What we do know is the distance of the UFO from the B-52 and its azimuth direction from which this distance is measured. As a result, the UFO can be anywhere in half of a vertical circle in which the diameter would be the B-52 vertical line. The radius of this circle would be equal to the distance of the UFO echo and the orientation around the vertical axis corresponding to the azimuth of the echo in the radar photos.
Because the UFO can be anywhere around this half circle, the angle “Alpha” between the direction of the UFO and the nadir can have any value between 0 and ± 90 degrees. We cannot resolve this issue by examining solely one of the eleven photos that feature a clear echo but we have several radar photographs depicting echo variations. Therefore, we can allocate the variations by a modification of the angle alpha, even if the UFO remains at a constant distance. For instance, we can allocate the variations if the UFO is below the aircraft moving vertically, while remaining at a constant distance from the B-52. Let us examine this hypothesis in more detail. Specifically, let us hypothesize that the echo of the UFO is roughly at mid-distance from the ground echo, that is, below the aircraft and somewhat lateral to the left of the B-52.
To examine this hypothesis we have to generate a rough calculation of the attenuation of the radar echo in the direction of the UFO. Although we cannot infer this attenuation, we shall assume further that the reflectivity of the radar waves from the UFO are essentially the same as the ground, which would result in the same returned radar signal for the same distance. In other words, we should observe the same intensity of the echo for the ground and the UFO.
If the UFO is half the distance from the B-52 to the ground, we should see a signal 16 times stronger for the UFO than for the ground (16 = 2 at the 4th power). Photo 775 provides some support for this hypothesis; in this photo the intensity of the echo of the UFO is superior to that of the ground for a distance that seems comparable. The intensity of the echo of the UFO could also be reduced by a factor of 16 (12 dB) if the UFO was not at the same altitude as the B-52 (direction alpha = 90 degrees when there is no attenuation), but below the horizontal plane of the B-52 at an angle Alpha = 15 degrees, relative to the nadir:
- Sin (15°) = 0.259 and 1 / sin2 (15°) = 14.93 which is 11.74 dB.
Based on this formula we can calculate the following table:
We see that this hypothesis leads us to infer that, with the exception of photos 771 and 775, the UFO was below the aircraft at 12.8 degrees on average, or about 0.22 nm (411 meters) from the nadir direction of the antenna. Photo 771 shows that the angle Alpha is 32 degrees, which locates the UFO about 0.92 nm (1700 meters) from the nadir direction of the antenna. In photo 775 it appears that the UFO was at the same altitude as the B-52, provided that its reflectivity was the same as the ground. The hypothesis of a UFO located below the aircraft during the time of the photographs seems fairly appealing. In addition, as we shall see later, this assumption might also explain why photo 774 exhibits no echo, whereas contiguous photos do show an echo. The hypothetical location of the UFO below the aircraft and comparatively close to the nadir of the antenna would also explain why the ground approach radars at the air base were not able to differentiate the UFO’s echo from the echo of the B-52. This hypothesis becomes even more compelling when we consider that the aircraft was equipped with a transponder, which allows a reduction of the attenuation due to the distance (attenuation becomes proportional to the square of the distance instead of the fourth power).
Another interesting fact is that the dimensions of the UFO deduced from photo 775 (246 x 90 meters) are the most probable owing to the very good signal to noise ratio of this photo. However, we need to deduct the resolution in distance of the radar by 37 meters (120 feet). So the probable radar dimensions of the UFO are then in the order of 200 x 50 meters, which is quite large.