Precipitable-water measurements with sun-photometer

In this paper a method is described of retrieving precipitable water from sun-photometer measurements. The quantitative relationship between water vapor transmission and precipitable water is established by means of LOWTRAN 7 model. Calibration of the water vapor absorption channel is made through a modified Langley method. The good agreement between the sunphotometer and radiosonde water vapor retrieval indicates that this method is feasible. The sun-photometer is operated at Hefei to monitor the precipitable water within one year period. Characteristics of both diurnal evolution and within-one-year variation of the precipitable water and their relation with synoptic system as well as surface dew-point temperature are presented and analyzed. Errors in the retrieved precipitable water from the sun-photometer measurements are also calculated and discussed.