Instrument for rapid measurement of surface deformations of a 210ft radio telescope

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Abstract
A description is given of an instrument designed for the rapid measurement of the surface deformations of the 210ft (64 m) radio telescope at Parkes, Australia. The method is based on the measurement, from the vertex, of small differences in the angular positions of targets, fixed to the dish surface, at known radial distances. The results are recorded photographically for later analysis. It is shown that the instrument, in conjunction with auxiliary attachments, can measure the dish shape with errors not exceeding 1.2mm at the zenith, and deformation due to tilting of the telescope with errors generally not exceeding 1.5mm at a zenithal angle of 60°. A complete survey of the dish at any zenithal angle can be made in 9–13h. Measurements with the equipment also permit the radio axis of the dish, computed from the measured feed position and geometrical dish axis, to be related to the ‘vertical’ of the telescope (defined as the mean normal to the azimuthal track).

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