Quantifying Marine Boundary Layer Water Vapor beneath Low Clouds with Near-Infrared and Microwave Imagery

Abstract

his study investigates the synergy of collocated microwave radiometry and near-infrared imagery to estimate the marine boundary layer water vapor beneath uniform cloud fields. Microwave radiometry provides the total column water vapor, while the near-infrared imagery provides the water vapor above the cloud layers. The difference between the two gives the vapor between the surface and the cloud top, which may be interpreted as the boundary layer water vapor. In combining the two datasets, we apply several flags as well as proximity tests to remove pixels with high clouds and/or intrapixel heterogeneity. Comparisons against radiosonde and ECMWF reanalysis data demonstrate the robustness of these boundary layer water vapor estimates. Last, it is shown that the measured AMSR-MODIS boundary layer water vapor can be analyzed using sea surface temperature and cloud-top pressure information by employing simple equations based on the Clausius?Clapeyron relationship.