Aligning the GBT Quadrant Detector
John Shelton, an engineer at Green Bank, uses a transit scope to align the quadrant detector under the dish of the Green Bank Telescope. In order to measure the precise amount of movement of the feed arm due to wind, and to temperature and gravitational fluctuations, engineers installed a rangefinder and mirror system beneath the surface of the dish. The rangefinder is on the feed arm and points directly through a hole in the dish surface. There, it is reflected by a mirror into a measurement device that compares all relative movements of the feed arm that affect the distance measured by the ranger.
Credit: NRAO/AUI/NSF
