Thirty Meter Telescope Site Testing VII: Turbulence Coherence Time

Abstract

ABSTRACTAs one of the atmospheric turbulence figures of merit, the Thirty Meter Telescope (TMT) site-testing campaign is aimed at measuring the time constant that dictates adaptive optics observations. We hence present the coherence time statistics of the TMT candidate sites, measured using a Multi Aperture Scintillation sensor (MASS) and a Differential Image Motion Monitor (DIMM). We find, using radiosonde and NCEP reanalysis data, that the MASS underestimates the free atmosphere component of the coherence time by a factor of 1.73. After debias of the MASS data and including the ground layer component, we find median coherence times ranging from 4.2 to 5.6 ms for our five candidate sites. This is the seventh article in a series discussing the TMT site-testing project.