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Retrievals of Thick Cloud Optical Depth from the Geoscience Laser Altimeter System (GLAS) by Calibration of Solar Background SignalLaser beams emitted from the Geoscience Laser Altimeter System (GLAS), as well as other space-borne laser instruments, can only penetrate clouds to a limit of a few optical depths. As a result, only optical depths of thinner clouds (< about 3 for GLAS) are retrieved from the reflected lidar signal. This paper presents a comprehensive study of possible retrievals of optical depth of thick clouds using solar background light and treating GLAS as a solar radiometer. To do so we first calibrate the reflected solar radiation received by the photon-counting detectors of GLAS' 532 nm channel, which is the primary channel for atmospheric products. The solar background radiation is regarded as a noise to be subtracted in the retrieval process of the lidar products. However, once calibrated, it becomes a signal that can be used in studying the properties of optically thick clouds. In this paper, three calibration methods are presented: (I) calibration with coincident airborne and GLAS observations; (2) calibration with coincident Geostationary Operational Environmental Satellite (GOES) and GLAS observations of deep convective clouds; (3) calibration from the first principles using optical depth of thin water clouds over ocean retrieved by GLAS active remote sensing. Results from the three methods agree well with each other. Cloud optical depth (COD) is retrieved from the calibrated solar background signal using a one-channel retrieval. Comparison with COD retrieved from GOES during GLAS overpasses shows that the average difference between the two retrievals is 24%. As an example, the COD values retrieved from GLAS solar background are illustrated for a marine stratocumulus cloud field that is too thick to be penetrated by the GLAS laser. Based on this study, optical depths for thick clouds will be provided as a supplementary product to the existing operational GLAS cloud products in future GLAS data releases.
Document ID
20080045513
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
Authors
Yang, Yuekui (Maryland Univ. Baltimore County Baltimore, MD, United States)
Marshak, Alexander (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Chiu, J. Christine (Maryland Univ. Baltimore County Baltimore, MD, United States)
Wiscombe, Warren J. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Palm, Stephen P. (Science Systems and Applications, Inc. Lanham, MD, United States)
Davis, Anthony B. (Los Alamos National Lab. NM, United States)
Spangenberg, Douglas A. (Science Systems and Applications, Inc. Lanham, MD, United States)
Nguyen, Louis (NASA Langley Research Center Hampton, VA, United States)
Spinhirne, James D. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Minnis, Patrick (NASA Langley Research Center Hampton, VA, United States)
Date Acquired
August 24, 2013
Publication Date
January 1, 2008
Subject Category
Earth Resources And Remote Sensing
Distribution Limits
Public
Copyright
Public Use Permitted.

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