NASA Logo

NTRS

NTRS - NASA Technical Reports Server

Back to Results
Model studies of the beam-filling error for rain-rate retrieval with microwave radiometersLow-frequency (less than 20 GHz) single-channel microwave retrievals of rain rate encounter the problem of beam-filling error. This error stems from the fact that the relationship between microwave brightness temperature and rain rate is nonlinear, coupled with the fact that the field of view is large or comparable to important scales of variability of the rain field. This means that one may not simply insert the area average of the brightness temperature into the formula for rain rate without incurring both bias and random error. The statistical heterogeneity of the rain-rate field in the footprint of the instrument is key to determining the nature of these errors. This paper makes use of a series of random rain-rate fields to study the size of the bias and random error associated with beam filling. A number of examples are analyzed in detail: the binomially distributed field, the gamma, the Gaussian, the mixed gamma, the lognormal, and the mixed lognormal ('mixed' here means there is a finite probability of no rain rate at a point of space-time). Of particular interest are the applicability of a simple error formula due to Chiu and collaborators and a formula that might hold in the large field of view limit. It is found that the simple formula holds for Gaussian rain-rate fields but begins to fail for highly skewed fields such as the mixed lognormal. While not conclusively demonstrated here, it is suggested that the notionof climatologically adjusting the retrievals to remove the beam-filling bias is a reasonable proposition.
Document ID
19950048946
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Ha, Eunho
(Texas A&M University College Station, TX, United States)
North, Gerald R.
(Texas A&M University College Station, TX, United States)
Date Acquired
August 16, 2013
Publication Date
April 1, 1995
Publication Information
Publication: Journal of Atmospheric and Oceanic Technology
Volume: 12
Issue: 2
ISSN: 0739-0572
Subject Category
Meteorology And Climatology
Accession Number
95A80545
Distribution Limits
Public
Copyright
Other

Available Downloads

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