Mitigation of transient meteor events in sodium layer by TMT NFIRAOS

  1. Get@NRC: Mitigation of transient meteor events in sodium layer by TMT NFIRAOS (Opens in a new window)
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Proceedings titleSPIE - International Society for Optical Engineering. Proceedings
ConferenceAdaptive Optics Systems III, 1 July 2012 through 6 July 2012, Amsterdam
Article number844734
SubjectBurn up; Centroiding; Control architecture; Defocus; Focus measurement; Focus sensors; Frame rate; Meteor trails; Meteors; NFIRAOS; Normal condition; Shack-Hartmann; Simulink simulations; Sky coverage; Sodium layer; Spot displacement; TMT; Tracking errors; Wavefront errors; Blending; Computer simulation; Errors; Ionization of gases; Magnetohydrodynamics; Optical radar; Optimization; Sodium; Electric appliances
AbstractNFIRAOS Small meteors usually burn up near the bottom of the sodium layer. Meteor trails can lead to temporary dramatic changes in the altitude of the sodium layer. This altitude change is very rapid, typically over 1 second, and after some unpredictable period of 10-20 seconds, can transition back to the nominal mean altitude also in about 1 second. The altitude change is very drastic and can jump by up to 1 km which, on the face of it, would cause 4 micrometers defocus errors on LGS WFS measurements for a 30-m telescope, unless properly tracked. Measurements by the UBC Lidar detected ~20 meteor trails / hour, and of these, 1-2 are significant events. We report on a full end-to-end Simulink simulation for TMT NFIRAOS including: meteor events measured by the UBC Lidar; on-instrument NGS focus sensor running at 90 Hz (median sky coverage frame rate); optimal temporal blending with LGS WFS focus measurements; LGS WFS centroiding matched filter update and Truth WFS update very 3s; full trombone servo model including non-linear focus range vs stage position. We optimized our control architecture and traded off motor power dissipation versus residual wavefront error and Shack-Hartmann spot displacement and found range tracking errors induce 12 nm WFE in normal conditions and brief (1s) jumps of 30-80 nm WFE at the beginning and ending of meteor transients. © 2012 SPIE.
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AffiliationNational Research Council Canada (NRC-CNRC); NRC Herzberg Institute of Astrophysics (HIA-IHA)
Peer reviewedYes
NPARC number21269524
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Record identifier70e2b992-62d9-4908-a440-bfb42a23910a
Record created2013-12-12
Record modified2017-04-24
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