Consistency of MODIS surface BRDF/Albedo retrievals 1. Algorithm performance
Consistency of MODIS surface BRDF/Albedo retrievals 1. Algorithm performance
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Date
2003-03-08
Authors
Liang, Shunlin
Jin, Yufang
Lucht, Wolfgang
Schaaf, Crystal B.
Gao, Feng
Li, Xiaowen
Strahler, Alan H.
Advisor
Citation
Jin, Y., C. B. Schaaf, F. Gao, X. Li, A. H. Strahler, W. Lucht, and S. Liang, Consistency of MODIS surface bidirectional reflectance distribution function and albedo retrievals: 1. Algorithm performance, J. Geophys. Res., 108(D5), 4158, doi:10.1029/2002JD002803, 2003.
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Abstract
The first consistent year (November 2000 to November 2001) of global albedo product
was produced at 1-km resolution every 16 days from the observations of the Moderate-
Resolution Imaging Spectroradiometer (MODIS) instrument aboard NASA’s Terra
spacecraft.We evaluated the quality of the operational albedo retrievals in two ways: (1) by
examining the algorithm performance using the product quality assurance (QA) fields (this
paper) and (2) by comparing retrieved albedos with those observed at ground stations and
by other satellite instruments (in a companion paper). The internal diagnostics of the
retrieval algorithm adequately reflect the goodness of the model fit and the random noise
amplification in the retrieved albedo. Global QA statistics show that the RossThick-
LiSparse-Reciprocal model fits the atmospherically corrected surface reflectances very
well, and the random noise amplification factors for white sky albedo and reflectance are
generally less than 1.0. Cloud obscuration is the main reason for the activation of the
backup magnitude retrieval algorithm. Over the 60°S to 60°N latitude band, 50% of the
land pixels acquire more than six clear looks during 14–29 September 2001, and only 5%
of these pixels are inverted with the backup algorithm. The latitude dependence and
temporal distribution of the QA fields further demonstrate that the retrieval status mainly
follows the pattern of angular sampling determined by cloud climatology and the
instrument/orbit characteristics. A case study over the west coast of the United States shows
that white sky shortwave albedos retrieved from magnitude inversions agree on average
with those from full inversions to within 0.033 in reflectance units and have a slightly lower
bias ranging from 0.014 to 0.023. We also explored the effect of residual cloud and aerosol
contamination in the atmospherically corrected surface reflectance inputs in another case
study over southern Africa. The quality assurance procedure of the operational MODIS
bidirectional reflectance distribution function and albedo algorithm compensates for some
of these residual effects and improves the albedo retrieval results by an order of 0.005
(10%) in the visible for more than 12% of pixels.