Water Vapor Profiling over Ocean Surface from Airborne 90 and 183 GHz Radiometric Measurements Under Clear and Cloudy Conditions

Abstract

Radiometric measurements at 90 GHz and three sideband frequencies near the water vapor absorption line of 183.3 GHz were made with the advanced microwave moisture sounder (AMMS) aboard the NASA DC-8 aircraft over some regions of the Pacific Ocean during November 1989. These measurements were used to retrieve atmospheric water vapor profiles over ocean surface using the algorithm developed by Wilheit. The algorithm incorporates a mechanism to estimate cloud liquid water when the estimated relative humidity is greater than 95%. The results were compared with the estimated values from the measurements of special sensor microwave imager (SSMI) and TIROS operational vertical sounder (TOVS). The water vapor profiles estimated from AMMS are generally higher at low altitudes and lower at high altitudes compared to those from the TOVS measurements. Values of total precipitable water estimated from the AMMS and SSM/I are in general agreement. Cloud liquid water is retrieved from both AMMS and SSM/I measurements over the same general regions. The water vapor profiles retrieved from the AMMS show more fluctuations in these regions; frequently, there is a deficiency of water vapor at low altitudes. Most likely, the AMMS with only four channels of measurements cannot retrieve both water vapor and cloud information with authority. © 1993 IEEE