Statistics for the global applicability of retrieval algorithms for geophysical parameters using the SSM/I

Abstract

Brightness temperatures (TB), measured by the SSM/I (Special Sensor Microwave Imager) at 85.5 GHz (vertical and horizontal polarization) during August-November 1987 and January- March 1993, are examined over the Earth's oceans between 60' N and 60' S. Collected data are placed into regions of dimension 5' latitude by 5' longitude. For each region, an absorption and scattering regime is identified based upon the frequency of occurrence between the average brightness temperature ((TB85V + TB85H)/2) and the polarization difference (TB85V TB85H). A global distribution of sensitivities is then constructed which allows us to determine how often our new and improved algorithms can be used for computing various geophysical parameters: cloud liquid water (CLW), precipitable water (PW), sea surface temperature (SST), and sea surface wind speed (WS). Results indicate the algorithms can be applied 75-90 % of the time over the majority of the Earth's oceans. These algorithms will serve as a simulation study for the performance of the Multi-frequency Imaging Microwave Radiometer which is scheduled for launch in the year 2000. Additionally, a quantitative assessment of CLW distributions for nonprecipitating clouds is presented over selected oceanic regions. This gives insight into the amount and variability of CLW present in clouds within the radiometer's field of view. The results indicate little variability in subtropical regions with a median value around .05 k g/M2. Increased variability and higher