![]() ![]() Terrestrial laser scanners (TLS) have been used to measure the deformations in large reflector antennas due to gravity, but have not yet been used for measuring thermal deformations. To efficiently carry out these observations gravitational and thermal deformations have to be corrected. This suggests that using a commercial off-the-shelf terrestrial laser scanner it is possible to measure deformations induced by thermal gradients on a large parabolic reflector.Īstronomical observations in the molecule rich 3 mm window using large reflector antennas provide a unique view of the Universe. From these differences we estimate that it should be possible to bring the surface error of the GBT down to $240\pm6~\mu$m. The difference between the amplitudes of known deformations and those measured are $<140~\mu$m when the wind speed is $\lesssim2$ m s$^$. We find that when using differential measurements it is possible to accurately measure deformations corresponding to different Zernike polynomials down to an amplitude of 60 $\mu$m. We use the active surface of the primary reflector of the GBT to validate our method and explore its limitations. Our method involves the use of differential measurements to reduce the systematic effects of the terrestrial laser scanner. In this work we investigate the use of a terrestrial laser scanner to measure thermal deformations on the primary reflector of the Green Bank Telescope (GBT). Terrestrial laser scanners have been used to measure the deformations in large reflector antennas due to gravity, but have not yet been used for measuring thermal deformations. The individual actuators, it continues to be an essential tool to supportĪstronomical observations in the molecule rich 3 mm window using large reflector antennas provide a unique view of the Universe. ![]() The holography system is now fully integrated into the GBTĬontrol system, and by enabling the telescope staff to monitor the health of Gravity and thermal gradients, are in general agreement with finite-element By computing average images forĮach tier of panels from the holography images, we confirm that the magnitudeĪnd direction of the panel distortions, in response to the combination of Pattern have emerged which are consistent with a repetitive pattern in theĪperture due to systematic panel distortions. With greater than 60 dB of dynamic range. Improvement in the telescope beam pattern has also been measured at 11.7 GHz The expected improvement in the radiometric apertureĮfficiency has been rigorously modeled and confirmed at 43 GHz and 90 GHz. We have also performed manual adjustments of the corner Have allowed us to infer and apply improved position offsets for the 2209Īctuators which control the active surface of the primary mirror, therebyĪchieving a dramatic reduction in the total surface error (from 390 microns to Holographic images of the telescope mirror surface irregularities. We have used a geostationary satellite beacon to construct high-resolution Holography system installed on the Robert C. We describe the successful design, implementation, and operation of a 12 GHz
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