Abstract
Two parabolic reflector antennas are calibrated: one a converted WWII searchlight and one a fiberglass “sugar scoop.” The technique of calibration is to aim the main lobe of each antenna at a corner reflector mounted atop a 300-m distant 150-m high tower instrumented with meteorological sensors. Acoustic pulses 40 to 200 msec in length at several frequencies between 1 kHz and 5 kHz are propagated toward the reflector and subsequently reflected back toward the same antenna for reception. Data from the meteorological sensors are used to compute the expected spreading of the beam due to atmospheric turbulence, and this predicted beam shape is compared with the antenna gain pattern (measured a few Rayleigh distances from the apertures) by moving the reflector down the tower. To obtain a reasonable estimate of the mean log intensity, averaging must allow the wind variance to refractively move the main beam through a total of several Fresnel zones. This requires the averaging of 10 to 20 pulses.
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