Monitor And Research On Observing Condition At Optical Observatory Site

Improving the optical telescope capability of detecting faint object and distinguish its detailed structure not only require accurate telescope designing and manufacturing technique,but also need advanced telescope control method.Moreover,a good observation environment of the site is also crucial for fully realising the potential of the telescope.Therefore,the construction of an costly optical telescope should be based on long-term systematic environment test of the site.This is also important for rational and efficient operation of a telescope,to help formulating a flexible and realistic observing schedule for instance.In this thesis,we introduced the key elements of the optical site selection,including astronomical seeing,night sky brightness,water vapor and meteorological conditions.The principle and approaches of monitoring and the advantages and disadvantages of different equipment are analyzed.Finally,the data from long term monitoring of optical observation environment at Nanshan Observatory are processed and the results are present.Astronomical seeing is an important parameter to determine the imaging quality of optical telescope.It is a physical quantity used to describe the combined effect of complex atmospheric turbulence to the observing target astrology,and it also determines the limit to the diameter of a telescope.We used the SBIG to monitor the seeing conditions of the Nanshan Observatory The monthly changes of the seeing and the average changes of the nighttime period were analysed.Our work revealed that the seeing value FWHM of Nanshan is 1.74 ".The night sky brightness is originated from the natural light and human light source,and these will brighten the observation sky background and directly affect the limitation of the observation magnitude.We used the SQM for the continuous night sky brightness monitoring.We querying the weather observation log daily to select the whole clear night observation data,then used the Bessel formula to remove coarse error data,we then obtained the maximum value from daily record.The further analysis results in a night sky brightness value of 21.7 mag arcsec-2 for visible bands.Water vapor has an intermittent absorption zone in the infrared observation band from 10 nm to 100 nm.Hence observing at infrared band has a very demanding requirement to the atmospheric water vapor content which is usually not higher than 0.4g/cm2.In addition,the monitoring of the site environment also includes the temperature,relative humidity and wind speed,to ensure the effective work of telescope and other astronomical instruments.We used the CE-318 sun photometer and the PC-4 four-element automatic weather station to monitor the water vapor and meteorological parameters at Nanshan.Our analysis revealed average annual water vapor content of 0.9g/cm2,average temperature of 3.4 ℃ and average relative humidity of 57.3%.The winds are in the range of 2-3m/s,most in south-east direction.Our experience and methods applied in this work,as well as the monitoring results provide useful comparison and reference information for the other optical sites and the undergoing tests in China.