must therefore remain speculative in nature. If the UFOs are CO!l-
sidered to have been material objects, then they would have had to
have shifted positiun some tens of miles in the "two to four" seconds
while the pilot was looking down at his instruments. This does not
explain why they cOJ.tinue d to appear on the ground radar. The only
admissible hypothesis would seem to he that they became invisible as
the fighter approached, but this does not account for the fact that
they could not be picked up on airborne radar while the aircraft was
searching the area.
There is one hypothesis that s';,ems to fit all of the observed
facts: that the "ragged formation" was actually an inferior mirage
(see Section VI,Chapter 4). TIle angular conditions are satisfied:
the objects appeared "slightiy helow the level of the aircraft, II
and reflections of the sky above the hori zan would :~eem dark when
seen projected against the h3zy sky directly over the city. A layer
of heated air, trapped temporarily below a cooler layer by a stable
vertical wind shear, could produce a wavy interface that would reflect
the sky in a few spots. This phenomenon is qUite similar to the
familiar road mjrage. Like a road mirage it suddenly disappears when
one gets too close and the viewing angle becomes either too large or
too small.
If the warm air below , the source of which would presumably
have been the downtown area af Dctroit, were also considerably
moister than the cooler air ahove as is quite probable, then the
radio ref~active index would decrease q~ite suddenly across the inter-
face. '111 is would tend to produce anomalous propagati 011 r~ffects,
incll~ing false echoes, on rodar, and would explain why ground radar
could continue tracking the unknowns when the pilot and aL'lJorne
radar operator could no longer see them. 'n1(, airborne radar, p('in~
iml1lersed in the layer would probably no:': recoive All e~hoes of any
duration other ~han. perhaps, occasional random blips.
226
must therefore remain speculative i.n nature. If the UPOs are COll-
sidered to have been material objects, then they would have had to
have shifted position some tens of miles in the "two to four" seconds
while the pilot was looking dowll at his instruments. This does not
explain why they cOJ.tinue d to appear on the ground radar. The only
admissible hypothesis would seem to be that they became invisible as
the fighter approached, but this does not account for the fact that
they could not be picked up on airborne radar while the aircraft was
searching the area.
There is one hypothesis that s'~em" to fj t all of the observed
facts: that the "ragged formation" was actually an inferior mirage
(see Section VI, Chapter 4). TIle angular conclitions are satisfied:
the objects appeared "slightiy below the level of the aircraft,"
and reflections of the sky above the hori zon would !'eem dark when
seen projected against the h3ZY sky directly over the city. A layer
of heated air, trapped temporarily below a cooler layer by a stable
vertical wind shear, could produce a wavy interface that would reflect
the sky in a few spots. This phenomenon b qUite similar to the
familiar road mirage. Like a road mirage it suddenly disappears when
one gets too close and the viewing angle becomes either too large or
too small.
1£ the Ilarm air below. the source of which would presumably
have been the downtown area of Detroit, were also considerably
moister than the cooler air ahove as is quite probable, then the
radio refractiVe index would decrease q~itc suddenly across the inter-
face. 'l1lis would tend to produce anomalous propagation effects,
including false echoes, on radar, and would expln.in why ground radar
cuuld continue tracking the unknowns when the pilot and aL'iJorne
radar operator could no longer 5t'e them. 'nle airhorne radar, pein~
.ilr.l1lcrseu in the laycr would probably no'~ recoive AI' echoes of any
duration other ::han, perhaps, occasional random blips.
226