Mitigation of transient meteor events in sodium layer by TMT NFIRAOS

Glen Herriot; Craig Irvin

doi:10.1117/12.924926

13 September 2012 Mitigation of transient meteor events in sodium layer by TMT NFIRAOS

Glen Herriot, Craig Irvin

Proceedings Volume 8447, Adaptive Optics Systems III; 844734 (2012) https://doi.org/10.1117/12.924926
Event: SPIE Astronomical Telescopes + Instrumentation, 2012, Amsterdam, Netherlands

Abstract

NFIRAOS Small meteors usually bum up near the bottom of the sodium layer. Meteor trails can lead to temporary dra matic 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 I 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 (Is) jumps of 30-80 nm WFE at the beginning and ending of meteor transients.

Citation Download Citation

Glen Herriot and Craig Irvin "Mitigation of transient meteor events in sodium layer by TMT NFIRAOS", Proc. SPIE 8447, Adaptive Optics Systems III, 844734 (13 September 2012); https://doi.org/10.1117/12.924926

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