The optical turbulence profile from a SLODAR analysis of mWFS data is shown in the figure above (left).  This is the average of approximately 30 profiles obtained from data spread out over the four nights of the 88” runs corrected to the zenith.  As predicted the turbulence in the ground-layer is confined to within the first tens of meters.   Taking these data and the corresponding measurements from the Mauna Kea MASS/DIMM (MKAM) we find that the predicted level of residual phase after a GLAO correction (over 30 arcminutes) is well predicted by the free-atmosphere seeing (figure on the right).  The free-atmosphere seeing measured by mWFS (“SLODAR”) and the MKAM MASS (blue dots) though the integrated seeing is typically worse from SLODAR.  This is presumably due to dome seeing at the UH88”.  We also show a prediction of the GLAO correction from a Zernike reconstruction from the mWFS data.  By applying a correction consisting of the average Zernike modes over this half-degree field of view we reach a residual phase variance which is comparable to that predicted by the MKAM MASS (free-atmosphere seeing). 

Nov 2012 - Initial results from mWFS on the UH88”

A comparison between the mWFS derived seeing and the Mauna Kea seeing monitor (MKAM).   The “free-atmosphere” seeing (left) is derived from the integral of the optical turbulence above the highest altitude profiled by mWFS (about 400m) while for MKAM we’ve taken the MASS seeing.  The “ground-layer” seeing (middle) is derived from the mWFS profiled turbulence (h~40m to 400m for CFHT) and from the total integrated seeing (h>7m) and MASS free-atmosphere seeing on MKAM.  The good correlation between the two “GL” measurements is somewhat unexpected (given the different lower altitude limits of mWFS and MKAM).  The similarity points to the surface layer lifting up and flowing over the CFHT dome as is seen in the numerical computational fluid dynamics models for CFHT.    Finally, the “dome seeing” (here everything arising from altitudes within the CFHT dome) is not correlated with the measured ground-layer turbulence.  The at times strong dome seeing arises from a different physical mechanism from the ground-layer and is comparable in strength.

May 2013 - Initial results from mWFS on CFHT