Review of Twenty One Ground and

 

   Even during the later phase of the incident, when a clear moving target was detected, no confirmatory contact appears to have been made on the CPS-4 height-finder. (The F-94 was instructed by Shiroi to go to 5000', but it appears that this was only a tactical best-estimate based on the Haneda visual report.) This certainly could be considered as possible circumstantial evidence of a propagation or electronic anomaly, inasmuch as a concurrent HRI track on an electronically independent set with a different operating frequency would typically be considered a counterindication of AP, system noise or radio frequency interference.

 

   This is an interesting point. In the present case the precise wavelengths of the CPS-1 and CPS-4 sets are unstated, but both instruments were in fact Sband, operating in a similar EM region around 10 cms; and to the extent that their respective bandwidths were relatively close they would be proportionately likely to respond to AP conditions with similar false echoes - unlike a situation where a CPS-4 is operated in tandem with, say, an L-band CPS-5 surveillance set. This raises the question of why, given what one might call classic conditions for ducting to occur and the presence (ex hypothesi) of unusually sharp, stable, moving AP targets on the CPS-1, no targets of any kind were reported on the CPS-4 heightfinder. A possible answer is that the CPS-4 had already been discounted as ineffective (at the time of the earlier, AP-like contacts) due to excessive ground-clutter at low elevation angles, and the controller may have continued to encounter this problem or even given up altogether the attempt to acquire HRI contact with the target. This interpretation implies a differential susceptibility of surveillance and heightfinder sets to AP clutter at minimal elevations, and of course also requires the target being sought to be at a  minimal elevation. If these conditions are fulfilled, then the absence of heightfinder plots could no longer in itself be considered diagnostic of AP.

 

   Firstly, the approximate mean elevation at Shiroi of the CPS-1 target (assuming a real target) can be inferred: the F-94 at an altitude of about 5000' acquired radar contact with it at range 6000 yards and at a depression angle of 10 degrees, which places the true target altitude at this time at about 3500'; and therefore, during the times when the controller had a clear PPI target on which to azicate the heightfinder (that is, when the target's orbit took it out of the CPS-1 clutter and over the sea where it was intercepted) the mean elevation of this target at ranges of about 13-15 miles would be only about 2 or 3 degrees. The question then arises of the the likely differential performance of CPS-1 and CPS-4 scopes, possibly in the sort of AP conditions inferred, with targets at such low elevations.

 

   Now a typical surveillance beam with an approximate cosecant-squared vertical profile has a horizontal beamwidth on the order of 1 degree, whereas a typical nodding-fan height-finder like the CPS-4 has a vertical beamwidth also of about 1 degree but a horizontal beamwidth on the order of 4 degrees or so; and it can be seen that when the two sets have matched peak powers and pulse repetition frequencies (for matching range performance) then the total energy radiated per unit time through any 1 degree of elevation by the CPS-4 cannot be less than four times that radiated by the CPS-1, and will in fact be much greater because the CPS-1 output has to fill a much larger solid angle many degrees in elevation. (Even if the powers of the two sets are not matched - only that of the CPS-1 is known: 1 megawatt - and if the power of the CPS-4 is a more modest 500 kW, then the ratio of energy density per degree of elevation must still be on the order of 10:1.) A height-finder beam of 4 x 1 degrees, therefore, will radiate more energy into the solid angle defined by the top edge of the beam and the earth than will the 1-degree surveillance beam if that solid angle is less than about 4 degrees of elevation; and given that the heightfinder's antenna elevation is close to a critical grazing incidence for anomalous propagation of less than about 4 degrees then the onset of ground returns due to AP will be sooner for the height-finder. Put another way, in trapping conditions the 4-degree height-finder beam will have a ground-incident "footprint" four times as large per unit range as the surveillance beam, so that the ratio of the clutter signal to a point-target signal at a given range on the height-finder can be several times larger.

 

   What all this means in terms of relative performance is that, when "looking" for a target at elevations of only 2 or 3 degrees, the CPS-4 antenna can be radiating a great deal of its main-beam output (plus a good deal of sidelobe) into a surface duct at grazing angles liable to severe trapping, leading to clutter returns which would be likely to overwhelm any relatively weak signal from a point target above the duct; but the signal-to-noise ratio of the CPS-1 could be several times better in the same conditions, preserving the super-clutter visibility of the same point target.

 

   The absence of height-finder plots on this low-elevation target is therefore not necessarily inconsistent with the presence of a solid, radar-reflective body - at least, even though the fact remains consistent with anomalous propagation it is no longer a sufficient condition of that hypothesis. But what of the target tracked on the CPS-1? Can it be described as consistent with AP?

 

    Any kind of anomalous propagation is difficult to entertain in the circumstances. The correlation between X-band 3-cm airborne radar and S-band 10-cm ground radar indications has to be considered good, and the target behavior on either scope during this phase of the events is really not diagnostic of AP. The 2 x windspeed behavior of partial reflection echoes would appear to be entirely inconsistent with displayed speeds on the CPS-1 ranging from zero ("hovering occasionally") to at least 250-300 knots and probably in excess of 375 knots (430 mph) on departure, and the repeated orbital tracks cannot realistically be explained by waves propagating across an inversion surface. Low level winds were light, SSE, overlain by a SW airflow: there is no indication of any anticyclonic circulation of the order of 150 knots (175 mph), and the target headings would at various times have been transverse, or even converse, to either of these (light) winds. The presentation on the CPS-1 was sharply defined, that of "a bonafide moving target", which made two wide movements over an azimuth arc of about 40 degrees and back with a near-doubling of range, during which movements the only reported signal loss occurred due to its passage through the permanent ground clutter. This is not characteristic of an illusory track due to a series of sporadic AP returns from ground (or sea) targets. And when, on the second orbit, concurrent air-ground detection is achieved by independent fixed and mobile radars at very different wavelengths, pulse repetition frequencies and incidences, with correlating position and motion on both scopes, then AP seems out of the question.

 

   The hypothesis of a "ghost" reflection from the F-94 generating the target tracked on the CPS-1 appears to be ruled out. Such a ghost would always appear on the azimuth of the primary reflector (the aircraft) and at greater range proportional to the added trip time to the secondary reflector, yet it seems quite clear that the F-94 approached the target on a heading of 320 degrees (NW) and "followed" it in a starboard turn to the N, over the coast and "into our radar ground clutter". At no time during this track can F-94 and target have been on the same azimuth from Shiroi (some dozen-or-more miles NNE) and at no time can the target have been displayed at greater range - indeed the F-94 would have been at greater range almost the whole time. Furthermore the first orbit of the target was tracked before the F-94 was even airborne out of Johnson, and the notion of a "ghost" echo separating into "three smaller contacts, maintaining an interval of about ¼ mile" is incredible. Finally this hypothesis offers no explanation of the concurrent target painted by the airborne APG-33.

 

   No effect due to sidelobes, multiple-trip echoes, system noise, component failure, radio frequency interference, birds, insects, clear air turbulence, meteorwake ionisation, windborne debris or balloons seems even remotely adequate to the core multiple-radar episode in this case.

 

   Total tracking times were brief, but far from ephemeral: upwards of 90 seconds AI contact is a significant duration, with the very rapid scan and virtually continuous rate of renewal allowing ample time for the operator to estimate the target parameters and assure himself of a "bonafide" point contact. On the CPS-1 the first track was plotted in the clear (away from the ground clutter) for approximately ½ the orbital circumference, about 5 minutes at the mean estimated speed (neglecting stationary episodes) of 125 knots (143 mph), or > 20 paints at 4 rpm - longer if the unquantified hovering episodes are taken into account. The exact timing of the sequence of events is unclear, but roughly consistent assuming a ½-circuit time of about 7 minutes (28 paints per plotted  track): Shiroi had the target in clear contact on its first orbit "at the time of the scramble" - about 2355 - so if it had been picked up emerging from the clutter at, say, 2354 it would have been lost in the clutter again by about 000001; the landward half of the 4-mile-radius orbit would be completed in about the same time, leading to emergence from the clutter over the coast at about 000708 (this is consistent with IR-35-52's statement that the Shiroi controller's time for this event, "0017", showed a roughly "ten minute difference" from other personnel statements due to "typographical error"); by about 0012 the target would have been a little more than half way around the seaward sector of its orbit when it split into three, and by 0015 when Shiroi vectored the F-94 onto the larger target it would have been heading towards the coast again, accelerating now and soon lost on GCI radar whilst the F-94 continued in pursuit with the target on-scope until about 0017:30.

 

   No great precision can be claimed for this timetable, of course, due to the large number of missing data-points and the inherent ambiguity of timings which are at best approximate and quantised to the minute; but at the same time, no serious inconsistency emerges. It is notable that ground and airborne radar operators were in no doubt that they had contact with the same "definite" and "bonafide" moving target.

 

   The Haneda/Tachikawa visuals are certainly the most problemmatic part of the report, and how, or even whether, they are related to the radar events is difficult to establish with confidence. In the absence of exact times for the visual movements one can only say that there is a suggestion of angular motions which correlate in a qualitative way with the radar orbits. However, the general bearing of the light from Haneda does correlate with the general location of the radar target(s) over the N of Tokyo Bay; the independent line of sight from Tachikawa does intersect in this same area; and the loss of visual contact from Haneda does correlate at least approximately with the inferred departure of the radar target. These points of correspondence must be weighed against the inability of a C-54 pilot in the air to confirm the strangeness of what appeared to him to be a "brilliant star", the statement that the light appeared to ascend at approximately the rate of siderial revolution, and the failure of observers at Shiroi and the aircrew to visually confirm the Haneda sighting, all of which points are suggestive of an astronomical source. However the brightness, angular size and detailed structure of the object - all of which can fairly be regarded as reliably scaled and described, in terms of the usual standards of witness observation - as well as the less-reliably reported angular motion, are inconsistent with the known propagation properties of the atmosphere as they could affect the image of the brightest body in the NE sky at the time.

 

   The question of unknown propagation mechanisms therefore arises. In this connection one is struck by certain parallels between the structure of the object and that of the Jovian system: it appeared through binoculars as a disc with three or four small, faint lights disposed in an arc below it. The planetary disc of Jupiter and the four bright Gallileian satellites are quite easily observable through 7x50 binoculars - indeed, some acute observers can see these satellites with the naked eye under favourable conditions near maximum extension, although generally their magnitudes of between +6.3 and +5.1 are obscured by the glare of the planetary disc. Plainly the observers were not looking at Jupiter's true E azimuth, and even directly contrasted the object's apparent brightness with that of Jupiter, so that some kind of mirage image has to be assumed, displaced laterally by some 40-45 degrees for much of the observation,  an angle periodically reduced as the image dimmed and shrank back towards the E true bearing of Jupiter. This image would contain some distortion to account for the fact that the four equatorial satellites, which transit Jupiter close to the ecliptic plane, were optically shifted into a pendant arc. Brightening of the disc is also implied, as is some dilation of its image by about 4 diameters from Jupiter's 40 arc seconds to a scaled angle of about 3 arc minutes without observable chromatic aberration. One imagines that such an effect might require a stable, near-stationary "bubble" of severely abnormal refractive-index-gradient performing as a near-perfect achromatic lens.  A line of sight from Tachikawa to Jupiter might graze this local discontinuity at a shallower angle, leading to an abnormal appearance for observers there also, and this requirement would place the mirage-producing zone in the region of N Tokyo Bay where extremely unusual radar propagation phenomena were observed.

 

   It is probably safe to say that no such phenomenon has ever been described or modelled in the field of meteorological optics. There are extremely rare reports, however, which appear to indicate dramatic propagation anomalies of a nearly analogous kind. For example, Minnaert (1968) describes a remarkable double-sun which was photographed from a ship in the Indian ocean and witnessed by numerous passengers: an exact duplicate of the solar image, perfect as to colour, shape, size and elevation, appeared offset in azimuth to one side of the true sun. There appears to be no conceivable explanation of this effect in terms of known mirage phenomena, and it indicates that some extraordinary properties of the atmosphere remain to be understood. It is, of course, not excluded that some such atmospheric phenomena might conveniently be termed "UFOs", or may be hypothesised to occur in association with other phenomena which some might choose to call "UFOs".

 

   If one wishes to demur from these spectacular conjectures, then Capella remains the only plausible astronomical source in the NE sky. Novel propagation mechanisms aside, it may be relevant that the details of fine structure were observed through binoculars, which suggests an alternative to diffraction due to atmospheric mist: condensed moisture on the objective glasses or eyepieces (exterior temperature was 5 degrees F above the dew point, but humid conditions in the tower or taking the binoculars out of cooler storage before use might cause the lenses to mist) or trapped moisture or other defects between lens elements which might cause diffraction, internal flares and/or improper focussing. The central image might conceivably be smeared, within an array of fainter secondary images. The likelihood of this hypothesis seems negligible, however, given that the observations lasted upwards of 50 minutes; that tower binoculars would be in not-infrequent use and chronic defects would be noted; that other stars in the NE sky are sure to have shown up the effects of any misting; that motion of the binoculars would almost certainly reveal the cause of the diffraction/blurring; and that four experienced tower controllers would not be so plain stupid.

 

   The issue of the non-visibility of any light source from Shiroi or the interceptor remains difficult. One point worthy of note, however, is that according to Ruppelt (1956, p.247) who headed Blue Book at the time and discussed the case with Far East Air Force intelligence personnel, one of the tower operators "had the distinct feeling that the light was highly directional, like a spotlight." It is true that the F-94 would probably never have been within less than 45 degrees of the line-of-sight from Haneda during the interception; it is also true that, if the light was the object being tracked on radar, then at the  time of the F-94's arrival in the area from the NW - when it would almost certainly have crossed this line of sight, at least in azimuth, on its way down over the bay - the target was over the land at the farthest point of its orbit and the light (ex hypothesi) was only visible from Haneda as "a small light" which was "difficult to follow closely". Thus it is conceivable that the aircrew may never have been in a position to see a directional light source. This argument is not very strong, however, and the degree of directionality implied (a very high degree of collimation with virtually zero effective scattering from the beam) would seem to conflict with the apparent simultaneous visibility of the source from Tachikawa, bearing some 50 degrees away from Haneda. No easy explanation exists for the display observed at Haneda, and one must admit the probability that radar and visual "UFOs" are in some sense related; but no satisfactory integration of all the visual details with the radar events can be achieved at this time.

 

   In conclusion: The possibility exists that the early detection of three or four stationary targets on the low beam of the CPS-1 was due to anomalous propagation, for which there is indirect circumstantial evidence in the form of the general weather conditions and the inferred presence of considerable lowanlge clutter on the CPS-4. It is also true, however, that the visual object was in view from Haneda at this time on the correct bearing, possibly at lower elevation than that subsequently attained, and the targets may have been related. There is insufficient information to argue this point.

 

   During the later radar tracks, however, the indications appear to be in every respect consistent with the presence of at least one high-performance aerial object with a radar cross-section smaller than that of a normal jet fighter, capable of jet-speed evasion of a pursuing F-94 (then probably the most advanced in the air) and erratic variations of speed. Its CPS-1 track showed it "stopping, and hovering occasionally" during a roughly 25-mile circumference orbit at 100-150 knots, implying, if not actual stationarity (the 15-second renewal rate of the PPI is too slow, and the resolution too coarse, to allow full confidence in this judgement, the controller's "considerable experience" notwithstanding, and concurrent height data are lacking) then at least a repeated deceleration to a speed (in light winds) almost certainly well below the 94-knot stalling airspeed of an F-94.

 

  Despite the periodic obscuration of the target(s) due to ground clutter, it is unreasonable to attempt to dissociate the target tracked on the first orbit from that tracked on the second orbit, one component of which was in multiple radar contact during intercept and achieved a speed probably in excess of the F-94's 430 mph; the two behaviors appear to be the rationally related movements of a single object (or sub-resolution cluster of objects) which had an inordinate range of speed and gave evidence of intelligent, evasive action when illuminated by the radar of the F-94.

 

   The splitting  into three contacts immediately prior to F-94's intercept attempt, followed by rapid departure, strikingly suggests something analogous to a tactical manoeuvre responsive to potentially hostile engagement. The fact that one contact remained brighter, with two smaller targets separating out to ranges of some 400 yards, resembles the deployment of radar decoys and might be interpreted as a test of remote drones or active jamming to confuse hostile pursuit. But it is not believed that any such free-flying drones were being deployed by any known small jets in 1952. Infra-red decoy flares were probably  under development to counter the incoming generation of IR-guided Sidewinder missiles, but flares would not answer the radar description and would also have been highly visible to the aircrew. Launched missiles would not "maintain ¼ mile separation" from the parent aircraft. The active jamming technology to achieve such false targets was almost certainly unknown in the world of 1952 analogue electronics, and the range of performance indicated is unmatched by any vehicle known to have been flying in 1952.

 

STATUS: Unknown

 

 

7.  DATE: December 10, 1952     TIME: 1915 local                CLASS: R/V air radar, air

                                                                                                                         visual

LOCATION: Odessa,

Washington            SOURCE: Thayer, Condon 1970, 140                 
                       

                                                    RADAR DURATION; unspecified

 

EVALUATION: Thayer - probable balloon

 

PRECIS:  The crew of a 2-seat F-94 flying between 26-27,000' near Odessa at 1915 sighted a very large, round white object which they estimated to be "larger than any known type of aircraft". It appeared to emit faint reddish light from two "windows". Its apparent movements were erratic. It performed a chandelle in front of the aircraft, seemingly able to "reverse direction almost instantly", the closed with the aircraft head-on at high speed before suddenly seeming to stop and break away. Fearing imminent collision the pilot banked the F-94 into a turn. They lost sight of the object at this time and never reacquired it visually, although the weather was clear over an undercast at 3000'. However 15 minutes later at 1930 a target was acquired on the airborne radar: It was moving generally west to east at about 75 knots. The crew believed this target was related to the earlier object, but no simultaneous visual sighting was made.

 

NOTES:  It appears that earlier Blue Book studies concluded that the visual object was a mirage of Venus. However, Thayer's 1968 analysis contains the Spokane radiosonde profile (release time 1900 LST) which does not indicate the presence of  temperature inversions near the aircraft altitude. A slight inversion is present at about 30,500' but this is much too far above the aircraft altitude to satisfy the small grazing angle requirement. Furthermore the small (order of 1/2 degree maximum) image wander due to mirage would seem inconsistent with the extent of motion reported, and the complete disappearance of the source - Venus being a brilliant object that would remain prominent in the clear sky even if the aircraft moved away from the critical mirage angle - is not convincingly explained.

 

Thayer observes that the Spokane radiosonde release time of 1900 is close to the time of the sighting, and that the appearance and motions of the object are quite characteristic of an encounter with a lighted balloon (saving some peculiar details such as "reversals" in front of the aircraft and the object's disappearance). Further, he observes that a balloon would have risen to at least 17,000' in 15 minutes and that the winds at the highest level plotted for the Spokane profile (18,000') are 260 degrees at 66 knots - not inconsistent with the reported easterly motion of the radar target at 75 knots.