The DIMM Seeing and UT Image Quality
|ISAAC (horizontal) vs. DIMM (vertical) at ISAAC observing airmass and wavelength before and after correction of DIMM seeing for finite Outer Scale. The original DIMM seeing (zenith and 0.5mu) is given to show the amplitude of the correction (green crosses). In good seeing conditions, DIMM (L0=25m) predicts better IQ than measured by ISAAC.|
|The comparison is now made at zenith and 0.5mu: DIMM seeing (horizontal) vs. ISAAC IQ (vertical) before and after inverse correction of ISAAC IQ for infinite L0. The raw ISAAC IQ is given to show the amplitude of the correction (green crosses). In good seeing conditions, ISAAC IQ (infinite L0) is worse than DIMM seeing.|
|DIMM predicted seeing at ISAAC observing wavelength before and after correction for finite outer scale, for all the observations of the database. At ISAAC wavelength and with a large telescope, the images have 30% better quality than the site seeing.|
DIMM indeed characterises the site seeing, as a proof the the good agreement of DIMM and UT4 active optics hartmann FWHM, both using apertures much smaller
The quality of the images obtained with large telescopes is better than the site seeing, the correction varies from a few % to a few hundred % depending on wavelength and seeing conditions.