Low-Level Water Vapor Fields from the VISSR Atmospheric Sounder (VAS) “Split Window” Channels

Abstract

A simple physical algorithm is developed which calculates the water vapor content of the lower troposphere from the 11 and 12 ?m (split window) channels on the VISSR Atmospheric Sounder (VAS) on the Geostationary Operational Environmental Satellites (GOES). The algorithm is applied to a time series of VAS split window radiances observed at 15 km horizontal resolution over eastern North America during a twelve hour period on 13 July 1981. Color coded images of the derived precipitable water (g cm?2) fields show vivid water vapor features whose broad structure and evolution are verified by the radiosonde and surface networks. The satellite moisture fields also reveal significant mesoscale features and rapid developments which are not resolved by the conventional networks. The VAS split window clearly differentiates those areas in which water vapor extends over a deep layer and is more able to support convective cells from those arms in which water vapor is confined to a shallow layer and is therefore less able to support convection. The spatial and temporal continuity of the water vapor features indicates very good relative accuracy, and point verification at radiosonde sites indicates fair absolute accuracy. Surface temperature variations are very effectively removed by the algorithm. Consequently, the VAS split window could be used operationally to monitor mesoscale developments in the low-level moisture fields over relatively cloud-free areas of the United States.