Retrieval Of Total Column Water Vapor With Multi-filter Rotating Shadow-band Radiometer

MFRSR (multifilter rotating shadow-band radiometer) uses automated rotating shadow-band technique to make measurements of total horizontal and diffuse horizontal irradiances at seven wavelengths simultaneously, and infer direct normal irradiance. The MFRSR has seven wave bands which measure visible and near-IR solar irradiance. Six of these wave bands are narrow bands, approximately 10 nm wide, centered on 414.3, 495.3, 613.7, 671.5, 867.6 and 939.3nm and these sets of wavelengths are sensitive to ozone absorption, water vapor absorption, aerosol scattering; the seventh measures the entire spectrum over 300-1100nm.In this paper, our main purpose is to retrieve total column water vapor (TCWV) with MFRSR at XiangHe. Firstly, we introduce the instrument of MFRSR and its measurement principle, and also introduce several relative methods of TCWV. The Langley method and modified Langley method were applied respectively for calibration in water vapor band based on the instrument characteristic of MFRSR. Then the water vapor transmission parameter counted by MODTRAN. Using the calculated data mentioned above, we eliminated the effect of aerosol optical depth and Rayleigh scattering in water vapor band, and the TCWV was derived from September 23, 2004 to June 20, 2005 at XiangHe. In order to illuminate the reliability of TCWV from MFRSR, we compared the results of MFRSR with AERONET data. The comparison is satisfaction and the TCWV derived from MFRSR is believable. The seasonal, monthly and daily variations of water vapor at XiangHe were analyzed using the TCWV. At last, we also compared the results of MFRSR with MODIS Near-Infrared Total Precipitable Water Product (MOD05), and the reasons why the difference aroused between them were carefully discussed.