To this date, experimental data useful for understanding the dome
seeing phenomenon may appear surprisingly scarce if one consider
the impact of the problem on the quality of
observations (see section 
).
There are some reasons
for this lack of reliable measurements.
One reason is due to the difficulty of measurements methods. Dome seeing is only one of several sources of image spread, which include in particular natural seeing which has a very high variability. There are no direct methods for the distinct evaluation of the local contribution to seeing which is caused by thermal turbulent inhomogeneities in and around the telescope. Only if a large collection of homogeneous and precise data of image quality together with all relevant environmental parameters are available, it is possible to perform a statistical analysis in which the local seeing effects effects can be outlined through the fluctuations of the natural seeing. Local seeing is of course more easily detectable on sites where the average natural seeing is low.
Unfortunately the operating procedures of most astronomical observatories do not particularly facilitate such measurements. Astronomical observatories are generally operated as service institutions for the use of individual astronomers. Requests for observing time on the best telescopes far exceeds the availability. A severe selection is done on proposed observing programs and successful astronomers typically obtain observing runs of 2 to 4 nights during which they are hard pressed to perform all the intended observations. Therefore this continuous shift of observers, whose priorities are their own immediate observation objectives, is an operational obstacle to the establishment of research programs on local seeing, which will take a fraction of observing time over long periods, and only offer eventually a perspective for quality improvements.
To this date the Canadian-French-Hawaii Telescope is the only observatory in which image quality, temperature and wind data are systematically taken and therefore provides the best database for studying dome seeing. Thanks to the courtesy of the CFHT direction, the author had access to this important set of data, which was analyzed for the first time in its entirety.
Figure: The Canadian-French-Hawaii Telescope