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| Titel |
Scientific impact of MODIS C5 calibration degradation and C6+ improvements |
| VerfasserIn |
A. Lyapustin, Y. Wang, X. Xiong, G. Meister, S. Platnick, R. Levy, B. Franz, S. Korkin, T. Hilker, J. Tucker, F. Hall, P. Sellers, A. Wu, A. Angal |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 7, no. 12 ; Nr. 7, no. 12 (2014-12-10), S.4353-4365 |
| Datensatznummer |
250115989
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| Publikation (Nr.) |
 copernicus.org/amt-7-4353-2014.pdf |
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| Zusammenfassung |
| The Collection 6 (C6) MODIS (Moderate Resolution Imaging Spectroradiometer) land and atmosphere data sets are scheduled for
release in 2014. C6 contains significant revisions of the calibration
approach to account for sensor aging. This analysis documents the presence of
systematic temporal trends in the visible and near-infrared (500 m) bands of
the Collection 5 (C5) MODIS Terra and, to lesser extent, in MODIS Aqua
geophysical data sets. Sensor degradation is largest in the blue band (B3) of
the MODIS sensor on Terra and decreases with wavelength. Calibration
degradation causes negative global trends in multiple MODIS C5 products
including the dark target algorithm's aerosol optical depth over land and
Ångström exponent over the ocean, global liquid water and ice cloud
optical thickness, as well as surface reflectance and vegetation indices,
including the normalized difference vegetation index (NDVI) and enhanced
vegetation index (EVI). As the C5 production will be maintained for another
year in parallel with C6, one objective of this paper is to raise awareness
of the calibration-related trends for the broad MODIS user community. The new
C6 calibration approach removes major calibrations trends in the Level 1B
(L1B) data. This paper also introduces an enhanced C6+ calibration of the
MODIS data set which includes an additional polarization correction (PC) to
compensate for the increased polarization sensitivity of MODIS Terra since
about 2007, as well as detrending and Terra–Aqua cross-calibration over
quasi-stable desert calibration sites. The PC algorithm, developed by the
MODIS ocean biology processing group (OBPG), removes residual scan angle,
mirror side and seasonal biases from aerosol and surface reflectance (SR)
records along with spectral distortions of SR. Using the multiangle
implementation of atmospheric correction (MAIAC) algorithm over deserts, we
have also developed a detrending and cross-calibration method which removes
residual decadal trends on the order of several tenths of 1% of the
top-of-atmosphere (TOA) reflectance in the visible and near-infrared MODIS
bands B1–B4, and provides a good consistency between the two MODIS sensors.
MAIAC analysis over the southern USA shows that the C6+ approach removed an
additional negative decadal trend of Terra ΔNDVI ~ 0.01 as
compared to Aqua data. This change is particularly important for analysis of
vegetation dynamics and trends in the tropics, e.g., Amazon rainforest, where
the morning orbit of Terra provides considerably more cloud-free observations
compared to the afternoon Aqua measurements. |
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