The Day-time Seeing Monitor at Fuxian Lake and Some Primary Results

A new instrument named SDIMM (Solar Differential Image Motion Monitor)is developed to detect the daytime seeing in Yunnan Observatory,which is based on differential image motion method 2,6 .The main body of the new instrument is a 300mm Maksutov telescope which has an adjustable slit put on the main focus plane.The slit is put at right angles to the solar limb,another lens collimate the light to parallel beam.A mask which has two sub-apertures is put in the parallel beam,one of these sub-apertures is covered by a little prism which changes the direction of the light with a littel angle,then the image lens behind the mask images two slit images on a video CCD.The equivalent diameter of sub-apertures is 56mm,the equivalent separation between two sub-apertures is 225mm,the sample rate is 12Hz,and exposure time of each sample is 7ms.The Fried parameter r 0 is calculated from 200 samples and need 17 seconds for sampling and calculation.The SDIMM also has an auto guide system and a precipitable water vapor detector. The SDIMM has been used in the solar site testing near the Fuxian lake since Apr.1998.Later in Nov.1999,one of the authors(Beckers) built a Scintillometer system in the new site near Fuxian lake.The data obtained from SDIMM and Scintillometer are compared, and the characteristics of these two instruments are discussed in this paper. The difference between the mountain-site and the lake-site will be discussed elsewhere.The conclusion of difference between the mountain-site and the lake-site is simply reported in this paper.