Further Study on the Calculation and Statistics of the three Subaperture DIMM

The atmospheric turbulence is an important factor that affects the image quality of optical telescopes. From the point of view of the site testing, its origination, characteristics, and influence on the wave-front of the star light are described in detail in this paper. The atmospheric seeing that represents the atmospheric quality is introduced. The different measurment methods of the atmospheric seeing and the principle of the differential image motion monitor (DIMM)are also presented. The optical structure and hardware system of the three sub-apeture DIMM in Yunnan Observatory are described in more detail. The difference between the Waldie method and the Roddier method for calculating the atmospheric seeing is theoretically analysed. Programs by using the Roddier method are presented and applied to the seeing observations.