Evaluation of the SSM/I Rain Analyses for Selective Storms in the ERICA Project
Abstract
Evaluation of the SSM/I HAC precipitation algorithm is presented. SSM/I rain rate data from five passes during ERICA IOP 2 and 3 were compared to all available ship observations, dropwinsonde soundings and coastal radar. Four different techniques were applied to the seven SSM/I channels to analyze rain rate. They are: SSM/I HAC algorithm, the Tb(19H) GHz channel with a threshold of 160 deg K, the Tb(37H) GHz channel with a threshold of 190 K, and the Tb(37V- 37H) image with a threshold of less than a 30 deg K difference. For the two IOP 2 passes the Spencer et al (1989) Polarized Correction Temperature (PCT) algorithm using the two 85 GHz channels were also studied. There is considerable uncertainty in the interpretation of the SSM/I HAC rain rate algorithm. Specifically large areas of out-of-limit values are present in the vicinity of mid-latitude winter cyclones. Study of the SSM/I HAC rain rate has indicated the out-of-limit areas occur when the rain flag is triggered, but the calculated rain rate from the HAC algorithm is less than zero. From this study it is obvious that the four channel SSM/I HAC regression algorithm, in its current form, can not satisfactorily analyze the precipitation. Further study is needed to determine if a regression equation can be used to estimate precipitation areas, particularly those with light precipitation. Treating the out-of-limits values as light precipitation would dramatically improve the quality of the SSM/ I HAC analysis. However, if a regression equation can not be used to estimate precipitation, using the Tb(37H) channel for a better overall analysis of light precipitation and showers and the Tb(19H) channel for a better analysis of the moderate to heavy precipitation is a viable solution.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 1990
- Accession Number
- ADA241321
Entities
People
- Edmund F. Cataldo Iii
Organizations
- Naval Postgraduate School