Island- and Ship-based Infrared and Microwave Radiometric Measurements of Atmospheric Water During ASTEX

The Wave Propagation Laboratory (WPL) operated infrared (IR) and microwave radiometers for measurement of atmospheric water substance from two platforms during the Atlantic Stratocumulus Transition Experiment (ASTEX). A three-channel (20.6, 31.7, and 90 GHz) microwave radiometer, a narrow-band 10.7 micrometer IR radiometer, and short- and long-wave radiometers were operated on Porto Santo Island, Madeira. A two-channel (23.8 and 31.7 GHz) radiometer and 10.7 micrometer IR radiometer were operated onboard the NOAA research vessel Malcolm Baldrige. Supporting data from Colorado State University (Porto Santo) and WPL (Baldrige) included radiosondes, lidar ceilometers, wind profilers, and other instruments.

We present various inter-comparisons from ASTEX: measured brightnesses with values predicted by current absorption models, precipitable water vapor derived from microwave radiometer data and that measured by radiosondes, and solar irradiance and liquid water path. We present a statistical summary of the water vapor and cloud liquid measurements and compare ASTEX results with marine stratocumulus cloud data from San Nicolas Island.

The island- and ship-board observations during ASTEX are examined for evidence of island-induced effects on precipitable water vapor and liquid water. The implications for use of island-based remote sensors for satellite data verification are described.