Comparison of columnar water-vapor measurements from solar transmittance methods

In the fall of 1997 the Atmospheric Radiation Measurement program conducted a study of water-vapor-abundance-measurement at its southern Great Plains site. The large number of instruments included four solar radiometers to me asure the columnar water vapor (CWV) by measuring solar transmittance in th e 0.94-mum water-vapor absorption band. At first, no attempt was made to st andardize our procedures to the same radiative transfer model and its under lying water-vapor spectroscopy. In the second round of comparison we used t he same line-by-line code (which includes recently corrected H2O spectrosco py) to retrieve CWV from all four solar radiometers, thus decreasing the me an CWV by 8-13%. The remaining spread of 8% is an indication of the other-t han-model uncertainties involved in the retrieval. (C) 2001 Optical Society of America.