During test runs of the new ASR-2 radar equipment, a large number of unidentified moving targets appeared on the scope at approximately 4 p.m. The sun was low in the sky, and the sky was clear of all clouds. Ceiling and visibility were unrestricted. Pilot temperature reports from a departing aircraft indicated that a pronounced temperature inversion existed at the 6,000-foot level.
Although no targets were plotted, a check on several indicated that their movement corresponded to the direction of the wind at the inversion level, with a velocity roughly double the wind velocity. Targets were larger, stronger, and more numerous than those observed by the writers during the Washington observations. At times the clutter made it difficult to keep track of actual aircraft targets on the scope.
At approximately 4 p.m., a group of similar targets appeared on the Indianapolis ASR-2 scope. Again the sky was clear of clouds; ceiling and visibility were unrestricted. Targets were strong. numerous, and of various shapes and sizes.
A simultaneous check of the L-band radar showed that only a few targets were being picked up by this equipment. The L-band targets appeared considerably weaker than those seen on the ASR-2 scope, although L-band aircraft targets appeared normal.
By manipulation of the ASR-2 antenna motor switch, it was possible to slew the antenna to beam it directly at some of the unidentified targets. The video return was displayed on an A-scope for closer analysis of the target characteristics. Comparisons were made with the A-scope characteristics of aircraft targets.
Aircraft targets showed sharp rise a "decay times as well as relatively constant shape and amplitude. The unidentified targets showed gradual rise and decay times, amplitude and shape showed wide variation which resulted in a random interlaced sign envelope similar to that returned by rain and cloud formations. These target characteristics are sketched in Fig. 15.