NASA Logo

NTRS

NTRS - NASA Technical Reports Server

Back to Results
Quantifying Global Uncertainties in a Simple Microwave Rainfall AlgorithmWhile a large number of methods exist in the literature for retrieving rainfall from passive microwave brightness temperatures, little has been written about the quantitative assessment of the expected uncertainties in these rainfall products at various time and space scales. The latter is the result of two factors: sparse validation sites over most of the world's oceans, and algorithm sensitivities to rainfall regimes that cause inconsistencies against validation data collected at different locations. To make progress in this area, a simple probabilistic algorithm is developed. The algorithm uses an a priori database constructed from the Tropical Rainfall Measuring Mission (TRMM) radar data coupled with radiative transfer computations. Unlike efforts designed to improve rainfall products, this algorithm takes a step backward in order to focus on uncertainties. In addition to inversion uncertainties, the construction of the algorithm allows errors resulting from incorrect databases, incomplete databases, and time- and space-varying databases to be examined. These are quantified. Results show that the simple algorithm reduces errors introduced by imperfect knowledge of precipitation radar (PR) rain by a factor of 4 relative to an algorithm that is tuned to the PR rainfall. Database completeness does not introduce any additional uncertainty at the global scale, while climatologically distinct space/time domains add approximately 25% uncertainty that cannot be detected by a radiometer alone. Of this value, 20% is attributed to changes in cloud morphology and microphysics, while 5% is a result of changes in the rain/no-rain thresholds. All but 2%-3% of this variability can be accounted for by considering the implicit assumptions in the algorithm. Additional uncertainties introduced by the details of the algorithm formulation are not quantified in this study because of the need for independent measurements that are beyond the scope of this paper. A validation strategy for these errors is outlined.
Document ID
20070023726
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Kummerow, Christian
(Colorado State Univ. Fort Collins, CO, United States)
Berg, Wesley
(Colorado State Univ. Fort Collins, CO, United States)
Thomas-Stahle, Jody
(Colorado State Univ. Fort Collins, CO, United States)
Masunaga, Hirohiko
(Colorado State Univ. Fort Collins, CO, United States)
Date Acquired
August 23, 2013
Publication Date
January 1, 2006
Publication Information
Publication: Journal of Atmospheric and Oceanic Technology
Publisher: American Meteorological Society
Volume: 23
Issue: 1
Subject Category
Meteorology And Climatology
Funding Number(s)
CONTRACT_GRANT: NNG04H245G
CONTRACT_GRANT: NAG5-13694
Distribution Limits
Public
Copyright
Other

Available Downloads

There are no available downloads for this record.
No Preview Available