AIRCRAFT DETECTION BEFORE RADAR. As someone much of whose professional career has been spent obsessing over radar detection, tracking, and location, these historical photos of acoustical tracking of aircraft are fascinating.


Notice the azimuth ring to allow for direction finding. The two "antennas" are offset-fed parabolic dishes, much like you see today in satellite cable system antennas. It appears to me that the two are slightly offset in elevation, which would suggest an amplitude monopulse capability to estimate elevation angle as well as azimuth.


The pedestal the men are standing on suggests an azimuth ring for rotation to direction-find in azimuth. The two vertical plane horns on the right suggest a capability to estimate elevation angle. One man probably controls elevation; the other azimuth.


The final picture is clearly an AZ/EL capable system. Most likely the man on the right controls the azimuth-finding horns; the man on the left controls the elevation-finding horns, and the man in the center is a spotter using a telescope for visual detection. Once an aircraft is spotted, he would control fine guidance.

It's interesting to note how the details have changed, but not the process. We use phase interferometry today for the accuracy it provides, but the physical structure hasn't changed a whit.