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A method for combining passive microwave and infrared rainfall observationsBecause passive microwave instruments are confined to polar-orbiting satellites, rainfall estimates must interpolate across long time periods, during which no measurements are available. In this paper the authors discuss a technique that allows one to partially overcome the sampling limitations by using frequent infrared observations from geosynchronous platforms. To accomplish this, the technique compares all coincident microwave and infrared observations. From each coincident pair, the infrared temperature threshold is selected that corresponds to an area equal to the raining area observed in the microwave image. The mean conditional rainfall rate as determined from the microwave image is then assigned to pixels in the infrared image that are colder than the selected threshold. The calibration is also applied to a fixed threshold of 235 K for comparison with established infrared techniques. Once a calibration is determined, it is applied to all infrared images. Monthly accumulations for both methods are then obtained by summing rainfall from all available infrared images. Two examples are used to evaluate the performance of the technique. The first consists of a one-month period (February 1988) over Darwin, Australia, where good validation data are available from radar and rain gauges. For this case it was found that the technique approximately doubled the rain inferred by the microwave method alone and produced exceptional agreement with the validation data. The second example involved comparisons with atoll rain gauges in the western Pacific for June 1989. Results here are overshadowed by the fact that the hourly infrared estimates from established techniques, by themselves, produced very good correlations with the rain gauges. The calibration technique was not able to improve upon these results.
Document ID
19950040819
Document Type
Reprint (Version printed in journal)
Authors
Kummerow, Christian (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Giglio, Louis (Science Systems and Applications, Inc. Lanham, MD, United States)
Date Acquired
August 16, 2013
Publication Date
February 1, 1995
Publication Information
Publication: Journal of Atmospheric and Oceanic Technology
Volume: 12
Issue: 1
ISSN: 0739-0572
Subject Category
METEOROLOGY AND CLIMATOLOGY
Distribution Limits
Public
Copyright
Other