28 July 2010 Wind-induced pointing errors and surface deformation of a 10-m submillimeter antenna
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Abstract
Two types of field measurements on the Atacama Submillimeter Telescope Experiment 10-m antenna have been made to diagnose antenna oscillations in strong wind gusts and to reduce pointing errors due to static/quasi-static wind loadings. The measurements with seismic accelerometers on the reflector have been compared with those from axis angle encoders. Our results have confirmed that the dominant wind effects are at low frequencies, and have found that twist and pitching motion of yoke arms are the dominant source of pointing jitters and decrease with frequency along the Kolmogorov slope of -5/3. In the range from about 1 to 10 Hz, the servo-loop excites and dominates pointing error oscillations. For azimuth oscillations, the frontal wind has the largest effects, compared with side- or tail-wind. To improve pointing performance against static/quasi-static wind effects, we have implemented and tested an auxiliary auto-pointingcorrection system with a lookup table compiled from all-sky pointing measurements under strong winds, invoking the Taylor's "frozen turbulence" hypothesis. We have successfully demonstrated that use of upwind data from a nearby anemometer helps to reduce the pointing errors of static wind effects from 2.4 " rms (correction OFF) to 1.2 " rms (correction ON) under a mean wind speed of 9.3 m s-1.
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Nobuharu Ukita, Hajime Ezawa, Sachiko Onodera, Masao Saito, "Wind-induced pointing errors and surface deformation of a 10-m submillimeter antenna", Proc. SPIE 7733, Ground-based and Airborne Telescopes III, 77331D (28 July 2010); doi: 10.1117/12.857279; https://doi.org/10.1117/12.857279
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