Analysis of the Preliminary Measurements Taken by the Multi-Color Photometric System of the YNAO Sky Brightness Monitor

A modern Sky Brightness Monitor(SBM) is a precision instrument for measuring various atmospheric parameters. Such an SBM has been listed as an important instrument in our site survey program in the west China. We have used an SBM to obtain multi-color sky brightness data at Mt.Dashanbao, Zhaotong. Based on our careful analysis of the preliminary photometric data, we have found ways to improve the optical system for the SBM. We have also tested the improved SBM by collecting data at the site of Fenghuang Mountain, Kunming for a few times. The data are of good quality showing that the multi-color photometric system of the SBM can be used for the site survey in the west China for solar observation. It should be noted that the data used to test the SBM were collected during the dry season of Yunnan (from the end of 2010 to the beginning of 2011). The observational results show that the aerosol contents are almost same at the two sites indicating the atmospheric compositions of the two sites are stable. However, at Gaomeigu, Lijiang, the Rayleigh scattering effect weakens after high noon, and there is an obvious increase in aerosol content. There are significant differences among calibrated sky brightness intensities at Mt.Dashanbao, Fenghuang Mountain, and Gaomeigu. The average sky brightness intensity at Mt.Dashanbao is between 10ppm and 20ppm of the brightness of the solar disk center, that at Gaomeigu is about 10ppm, and that at Fenghuang Mountain is between 40ppm and 50ppm. These results objectively reflect the sky brightness intensities and atmospheric characteristics at different sites during a given period of time.