Scientific Study of Unidentified Flying Objects (the Condon Report, complete, three volumes)

25 to 65 ~nots aloft. TIle closest available radiosonde data
(International Falls 1200 (;~l'r 0600 I,ST) G September, show a tem-
perature inversion and strong humidity lapse through a layer
extending from 1029 - 1259 m. ahove the surface. The ~radient of
radio refractivity thl'ough this layer averaged -114N/km (corrected
for radiosonde sensor lag). This layer would be expected to show
a significant partial reflection at radio frequencies. tf the layer
were present over Finland AFB at the same elevation, it could have
produced false targets by partial reflection of real ground targets,
which would have apneared to be at altitudes of from 8,300 - ~'1,8()() fcet
because of the geometry of such reflected targets (seE- Section VI,
Chapter 5). This agrees well with the reported "UFO" altitudes of
8,000 - 10,000 ft.
A.nomalous propagation echoes are not usually confined to a single
direc1..ion. There are three possible explanations in this CB:;C and in
other similar cases: B single real object was ~eing tracked; the
radar operators were not looking for targets on other azimuths; the
part.: ally reflecting layer may have been anisotropi c (1. e. displ aying
a preferred direction for strongest reflection). There 15 no direct
physieal evidence for the existence of such anisotropic layers, but
no stDdies have been made to determine whether or not they might exist.
Apparent anisotropy in radar AP returns nas often been observed,
although not usually over such a narrow azimutll range as was apparently
the case at Finland AFB.
Regarding the visual reports submitted, the comment of the in-
vestigatinR offlc~r at Finland.AFB is of particular interest:
TIle next evening, at 2200 hours. the "white-red-green"
object reappeaTed ip the sky at exactly the same position
it had appeared on 5 S~ptember. '~is officer oh~~rvcd it
and detemined it to be a star which was near the horizon
180
lS to b5 ~nots aloft. TIle closest available radiosonde data
(International Falls 1200 (;~l'r noon 1ST) G Septemher, show a tem-
perature inversion and strong humidity lapse through a layer
extending from 102~ - 125~ m. ahov!:' the surface. The gradient of
radio refractivity thl"Ough this layer averaged -114N/km (corrected
for radiosonde sensor lag). This layer would be ex.pected to show
a significant partial reflection at radio frequencies. tf the l~yeT
were present over Finland AFB at the same elevation, it could have
produced false targets by partial reflection of real ground targets,
whi ch would have apneared to be at aIti tudes of from 8,300 - (", SOO feet
because of the geometry of such reflected targets (seE- Section VI,
Chapter 5). Th is agrees we 11 with t:he reported "UFO" a I t i tudes of
8,00n - 10,000 ft.
A.nomalous propagation echoes are not uStlfllly confined to a single
dire-C1.. i.on. There are three possible explanations 111 this case and in
other similar cases: a single real object was bein~ tracked; the
radar operators were not looking for targets on other azimuths; the
partially reflecting layer may have heen anisotropic (i.e. displaying
a preferred direction for strongest reflection). lhere IS no direct
physical evidence for the existence of such anisotropic layers, but
no st~dies have been made to determine whether or not they might exist,
Apparent gnisotropy in radar AP returns nas often been observed,
although not usually over sllch a narrow azimuth range as was apparently
the case at Finland APB.
Regarding the visual reports submitted, the comment of the in-
vestigatinM offlc~r at Finland.AFB is of particular interc~t:
TIle next evening. at 2200 hour~. the "wht to-rcd-.green"
object reqppeared ip the sky at exactly ~he ~ame position
it had appeared on fi C)t'ptember. 'l11is of,?i eer ob:H'rvetl it
and detemined it to he a star which was near thC' horizon
180