August 13-14, 1952; Washington D.C.
The observation period started at 1830 Eastern standard time (EST) on the evening of August 13. At the beginning of this period, the
moving target indicator was gated to cancel out ground returns up to a range of 10 nautical miles. Beyond this range the scope was clear
except for a few permanent echoes that were visible.
Suddenly, at approximately 1957 EST, a group of seven strong stationary targets became visible in an area about 15 miles north-northeast
of the radar antenna. During the next two or three antenna revolutions, the area on the scope between Washington and Baltimore became
heavily sprinkled with stationary targets in a belt about 6 miles wide. A group of additional targets became visible in an area approximately
10 to 15 miles south of the radar antenna. This was evidence of the beginning of a temperature inversion.
Within the next minute, at approximately 1958 EST. four unidentified moving targets showed up 5 miles southeast of the radar antenna
and moved in a southerly direction away from it. When the radar beam was switched from high to low, the targets disappeared. The beam
was switched back to high, and the targets returned.
Targets were uniformly small and usually had a weak, fuzzy appearance. However, the target intensity varied from sweep to sweep.
Occasionally one or two very strong returns would be received in succession, followed by almost total blanking.
For the next four and one-half hours, many unidentified targets were carefully plotted with a grease pencil on the face of the Type VG
scope. The time for each was entered on these plots in order to calculate ground speeds. To secure a permanent record, time data and<>track plots were transferred from the scope face to a sheet of frosted acetate. These plots are reproduced in
Figs. 1, 2, and
Fig. 3. The distribution of target ranges is shown in
Fig. 4. The average distance that any target was tracked continuously was approximately 2.1 nautical miles.
The observation period was discontinued at 0030 EST on August 14, and steps were taken to secure all available meteorological data
relevant to the observation period. The local radiosonde observation which was taken near the midpoint of the observation period,
at 2200 EST on August 13, is reproduced in
Fig. 5. Winds aloft, as observed at the same time, are listed in Table II.
A PRELIMINARY STUDY OF
UNIDENTIFIED TARGETS OBSERVED
ON AIR TRAFFIC CONTROL RADARS
Richard C. Borden, Electronics Division and
Tirey K. Vickers, Navigation Aids Evaluation Division
Technical Development -Report No, 180