The Second Term Site Survey in Gaomeigu Station,Lijiang—Comparative Observation of the Seeing Between No.3 and No.6 Hill

Based on the experience of many site surveys in the world,the seeing shows difference at various hills in the same site.In order to check the difference of the seeing at various hills in Gaomeigu site,we firstly observed at ten hills using the method of eye diffraction ring observation,then we selected No.3 and No.6 hills to do the comparative observation of the seeing using two of the three-subaperture DIMMs(Differential Image Motion Monitor) at the second term site survey.The two DIMM equipments have the same technical parameters and are installed on two 35cm telescopes respectively.Based on the statistical results of 4756 sets of observed data from 6 Feb.1999 to 31 Dec.1999,we have found the following results:(1) The average seeingis are 11.2623cm for No.3 and 11.5952cm for No.6. It is shown that two hills have no obvious difference for the seeing.This result is consistent with the previous eye diffraction ring observation.(2) There are 16 days in which the seeing in No.3 hill is better than one in No.6 (about 43.24%),while there are 21 days in which the seeing in No.6 hill is better than one in No.3 (about 56.76%).It shows that the seeing in No.6 is slightly better than one in No.3. (3) The curves of seeing variation with time were obtained in two days of 29 March and 16 May in 1999.It shows that the curves have a similar shape.(4) The curves with obviously different shapes in two hills were observed on 11 April in 1999.This situation could be caused by the local wind velocities and directions.In summary,the whole mountain in the Gaomeigu site has good seeing.No obvious seeing difference has been observed at the various hills in the Gaomeigu site.