Millimeter-wave measurements of low amounts of precipitable water vapor

Abstract

An experiment was conducted to measure low amounts of total-column precipitable water vapor (PWV). Extremely dry conditions commonly occur in polar regions during the winter months. Accurate measurements of the PWV during such dry conditions are needed to improve our understanding of the regional radiation energy budgets. D. C. Jones et al. (1998) have shown that the strength associated with the 183 GHz water vapor absorption line makes radiometry in this frequency regime promising for measuring low amounts of PWV. However, retrievals using these frequencies are complicated by uncertainties in absorption models and the fact that these frequencies also respond to the vertical temperature distribution as well as to liquid and ice clouds. NASA Goddard Space Flight Center and NOAA Environmental Technology Laboratory conducted an experiment to investigate millimeter wave measurements for making ground-based estimates of PWV during dry conditions. The experiment was conducted at the DOE's North Slope of Alaska/Adjacent Arctic Ocean Cloud and Radiation Testbed site located just outside Barrow, Alaska. NASA and NOAA deployed a suite of radiometers covering 28 channels in the frequency range of 20 GHz up to 340 GHz including 8 channels around the 183 GHz water vapor absorption line.