Estimation of seeing quality using low-resolution solar image data

Modulation transfer functions (MTFs). generated as a by-product of the anal ysis of low resolution solar images taken for the Global Oscillation Networ k Group, were used to estimate the quality of seeing at its six sites. Thes e MTFs, after approximate correction for the effects of the instrumental po int spread function, were fitted with physically-motived functional forms r epresenting the effects of seeing and scattering. It was found that the est imates of seeing quality were relatively robust to the effects of scatterin g, but were severely biased by effects caused by changes in instrumental fo cus. Relative trends in seeing quality are preserved on time scales shorter than a few months and it is found that local topography dominates the obse rved trends in daytime seeing quality.