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Seeing Monitors Installed at the Evans Facility...(1Sep92)
and the Vacuum Tower Telescope
(from NSO, NOAO Newsletter No. 31, 1 September 1992)

A non-telescopic method of determining the quality of seeing has been
developed for large angular-diameter objects, such as the Sun. In this
method the concept of thermodynamic fluctuations is used to relate the
observed intensity fluctuations (solar scintillations) to the RMS
angular diameter of the atmospheric seeing cells and the telescopic
angle of arrival fluctuations. Because the seeing monitors are
non-telescopic, the seeing measurements do not interfere with the
telescope operation. The seeing monitor detector at the Evans Facility
is mounted on the spar adjacent to the large coronagraph aperture. At
the Tower Telescope, the detector is placed at the vacuum periscope
feed, which provides an unvignetted view of the Sun directly from the
coelostat mirrors.  Analog outputs are provided from the monitors where
one volt represents an RMS seeing angle of one arcsecond.  Software is
available at each facility for digitizing and recording the seeing time
dependence, as well as camera threshold triggering at a given seeing
level. The method is applicable to nighttime measurements, using the
full moon as a source. However, more sensitive detectors would be
required.

E. J. Seykora, East Carolina University

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