A robust retrieval of water vapor column in dry Arctic conditions using the rotating shadowband spectroradiometer

A method to retrieve water vapor column using the 940-nm water vapor absorp tion band in dry Arctic conditions is presented. The retrievals with this m ethod are stable with respect to uncertainties in instrument radiometric ca libration, air pressure, solar source function, and aerosols. The water vap or column was retrieved with this method using spectra obtained with the ro tating shadowband spectroradiometer (RSS) that was deployed during an inten sive observation period near Barrow, Alaska, in March 1999. A line-by-line radiative transfer model was used to compute water vapor transmittance. The retrievals with this method are compared with retrievals obtained from thr ee independent measurements with microwave radiometers. All four measuremen ts show the same pattern of temporal variations. The RSS results agree most closely with retrievals obtained with the millimeter-wave imaging radiomet er (MIR) at its 183 GHz 7 double-side band channel. Their correlation over a period of 7 days when water vapor column varied between 0.75 mm and 3.6 m m (according to RSS) is 0.968 with MIR readings 0.12 mm higher on average.