Experimental laser system for monitoring deformations in large radio reflectors

The design of an instrument for rapidly measuring the changes in the profile of large steerable radio reflectors is described. Its use is illustrated by measurements of the reflector deformation of the UK Science Research Council´s 25m steerable aerial at Chilbolton, Hants., England, as the aerial is tilted and accelerated. The laser instrument surveys 36 points distributed on the reflector in 3s, and the overall accuracy of measurement as installed on the aerial is estimated to be within ±0.4mm(r.m.s.), with a repetition error of 0.2mm(r.m.s.). Lower figures should be achievable with smaller aerials.