Anomalous Echoes Captured by a B-52 Airborne Radarscope Camera:
A Preliminary Report
Radarscope photographs of unidentified radar indications were taken aboard a USAF B-52H flying NW of Minot AFB, North Dakota, on Oct 24 1968. The scope photos are briefly described followed by the radar equipment specifications. Some issues arising in the reconstruction of times and distances are then addressed, and finally some avenues of interpretation are explored in the light of the equipment specifications, flight data, and radar propagation issues. Explanations are attempted (see Section 6) in terms of aircraft and missiles, meteors, precipitation, moon returns, lightning (including lighting channel echoes, sferics, and ball lightning), auroral ionisation, birds, insects, satellites, RFI, internal noise, ECM spoofing, and anomalous propagation. No convincing explanation of the unidentified echoes is found.
The Air Force file contains discussion of a "pretty good" temperature inversion between 2000-5000ft and speculates that this may have been the cause of an "anomalous blip." However, since the radar refractive index (RI) is about five times more sensitive to changes in humidity than to changes in temperature, this is not very meaningful. In fact a correct N-unit profile of the refractivity gradient constructed (Section 6-11) from temperature and dewpoint data found in the Air Force file indicates no elevated RI anomalies. But the file data - lacking original date-time information and from a remote rawinsonde station - were found to be of doubtful relevance and even of doubtful provenance.
Reliable and more complete archival data were obtained from the US National Climatic Data Center for the nearest balloon releases bracketing the period of observation. These soundings indicate gradients generally quite close to the mean up to the highest readings at 500 mbar, with weak elevated subrefractive layers developing below the B-52 flight level. These features are only marginally (<5 N-units / kft) outside the nominal limits of "standard" refractivity and do not indicate any obvious cause of strong unexplained echoes on the airborne radar.
However, these are average gradients. It remains possible that undetected narrow layers of sharp RI gradient might fall between the samples, or that higher level tropopausal structures might exist off the top of the diagram. But both the echo presentation and its persistence at a constant azimuth during a significant period of straight flight seem impossible to explain as direct backscatter from even a highly efficient hypothetical layer, and the displayed range combined with strongly interlocking evidence of the B-52 altitude rules out a 1st-trip ground echo by any ray path.
A possible interpretation of a part of the photo sequence is offered in terms of 2nd-trip echoes from a terrain feature beyond the unambiguous range of the radar, combined with ghost echoes due to signals received via a dual ray path in unusual (hypothetical) atmospheric conditions. However, the one attractive candidate for such a topographical target is shown to be a minimum of about 30 degrees away from the true echo azimuth at any point on the flight track during the incident. The possibility of a large error in the recorded flight track, which would bring the position of the aircraft into coincidence with this theory, is shown to be inconsistent with radar-photographic evidence of the B-52's descent rate. Finally the official documentary and aircrew evidence in regard to the persistence of the radar contact at a constant bearing over a ground track of some 25 miles (in the order of 10 times the duration of the extant photo record) appears to be inconsistent with this hypothesis.
A very unusual type of interference from a very similar airborne pulse radar set at long range is considered theoretically possible, but the extremely strict conditions required render the theory very strained indeed. Several other theories are considered and rejected, generally on quite basic quantitative grounds, as either impossible or very unlikely.
In summary, although the available hard radar evidence cannot in itself constitute proof of the presence of one or more extraordinary airborne objects, it is concluded that explanations of the echoes so far considered are unconvincing. In general the probability of a highly unusual radar anomaly has to be estimated in the context of surrounding air/ground visual reports and other events detailed elsewhere by the principal investigators.
This study is based on digital scans of fourteen 8 x 10 photographic prints, Blue Book file information, interview transcripts, as well as technical and background data supplied by principle investigators Tom Tulien and Jim Klotz. This material is supplemented by additional technical specifications obtained by the author, independent measurements of the photos by Brad Sparks and Dr. Richard Haines, and further consultation with witnesses, investigators, and others. Appropriate rawinsonde datasets for the refractivity calculations in Section 6-11 were kindly provided by the US National Climate Data Centre, Asheville, NC. Detailed discussions with Dr. Claude Poher were helpful in improving an earlier draft of this report, leading to revision of some estimates of echo displacement in Section 5-3. The author also acknowledges the help of former B-52 radar-navigator Richard Sessler; a USAF M/Sgt and former B-52 bomb-nav radar technician who wishes not to be named but who contributed invaluable advice and documents; and Ed Doyle of Radio Research Inc., Waterbury, Connecticut.