Estimation of 3-D water vapor distribution using a network of compact microwave radiometers

Quantitative precipitation forecasting is limited by the paucity of observations of water vapor in the troposphere. In particular, severe storms have been observed to develop in regions of strong and rapidly evolving moisture gradients. Conventional measurements of water vapor density profiles are obtained using in-situ probes on-board weather balloons, including radiosondes. These in-situ profile measurements have high vertical resolution, but have severe limitations in both temporal and spatial sampling. Lidars use differential absorption techniques to estimate water vapor with comparable resolution to that of radiosonde observations. However, lidars are expensive, and their operation is limited to clear-sky conditions due to the high opacity of clouds at optical wavelengths. Inversion of brightness temperatures measured by upward-looking, ground-based microwave radiometers allows the estimation of vertical profiles with high temporal resolution in both clear and cloudy conditions. However, assimilation of retrieved water vapor fields with improved spatial coverage has the potential for more substantial impacts on numerical weather prediction of convective storm initiation. Measurements using a network of multi-frequency microwave radiometers can provide information to retrieve the 3-D distribution of water vapor in the troposphere.