NASA Logo

NTRS

NTRS - NASA Technical Reports Server

Back to Results
Nighttime Cirrus Detection using Atmospheric Infrared Sounder Window Channels and Total Column Water VaporA method of cirrus detection at nighttime is presented that utilizes 3.8 and 10.4 (micro)m infrared (IR) window brightness temperature differences (dBT) and total column precipitable water (PW) measurements. This technique is applied to the Atmospheric Infrared Sounder (AIRS) and Advanced Microwave Sounding Unit A (AMSU-A) instrument suite on board EOS-Aqua, where dBT is determined from sets of carefully selected AIRS window channels, while PW is derived from the synergistic AIRS and AMSU-A water vapor retrievals. Simulated and observed dBT for a particular value of PW are not constant; several physical factors impact dBT, including the variability in temperature and relative humidity profiles, surface emissivity, instrument noise, and skin/ near-surface air temperature differences. We simulate clear-sky dBT over a realistic range of PWs using 8350 radiosondes that have varying temperature and relative humidity profiles. Thresholds between cloudy and uncertain sky conditions are derived once the scatter in the clear-sky dBT is determined. Simulations of optically thin cirrus indicate that this technique is most sensitive to cirrus optical depth in the 10 (micro)m window of 0.1-0.15 or greater over the tropical and subtropical oceans, where surface emissivity and skin/near-surface air temperature impacts on the IR radiances are minimal. The method at present is generally valid over oceanic regions only, specifically, the tropics and subtropics. The detection of thin cirrus, and other cloud types, is validated using observations at the Atmospheric Radiation Measurement (ARM) program site located at Manus Island in the tropical western Pacific for 89 coincident EOS-Aqua overpasses. Even though the emphasis of this work is on the detection of thin cirrus at nighttime, this technique is sensitive to a broad cloud morphology. The cloud detection technique agrees with ARM-detected clouds 82-84% of the time, which include thin cirrus, as well as other cloud types. Most of the disagreements are well explained by AIRS footprint-scale heterogeneity compared to ARM point measurements, cirrus overlying lower-layer water clouds, possible mixed phase microphysics in midlevel clouds, and significant IR channel noise for cold BT scenes over deep convective towers.
Document ID
20070024429
Acquisition Source
Jet Propulsion Laboratory
Document Type
Reprint (Version printed in journal)
Authors
Kahn, Brian H.
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Liou, Kuo Nan
(California Univ. Los Angeles, CA, United States)
Lee, Sung-Yung
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Fishbein, Evan F.
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
DeSouza-Machado, Sergio
(Maryland Univ. Baltimore, MD, United States)
Eldering, Annmarie
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Fetzer, Eric J.
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Hannon, Scott E.
(Maryland Univ. Baltimore, MD, United States)
Strow, L. Larrabee
(Maryland Univ. Baltimore, MD, United States)
Date Acquired
August 23, 2013
Publication Date
April 2, 2005
Publication Information
Publication: Journal of Geophysical Research D07203, doi:10.1029/2004JD005430,2005
Volume: 110
Subject Category
Geophysics
Funding Number(s)
CONTRACT_GRANT: NGT5-30372
Distribution Limits
Public
Copyright
Other
Keywords
Atmospheric Radiation Measurement (RAM)
brightness temperature differences (dbt)
cirrus detection

Available Downloads

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