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Results From the Deep Convective Clouds-Based Response Versus Scan-Angle Characterization for the MODIS Reflective Solar Bands

TitleResults From the Deep Convective Clouds-Based Response Versus Scan-Angle Characterization for the MODIS Reflective Solar Bands
Publication TypeJournal Publication
Year of Publication2018
AuthorsAngal, A., X. Xiong, Q. Mu, D. R. Doelling, R. Bhatt, and A. Wu
JournalIEEE Transactions on Geoscience and Remote Sensing
KeywordsC6; calibration; collection 6; DCC; deep convective clouds; desert; Moderate-Resolution Imaging Spectroradiometer; MODIS; response versus scan angle; RVS

The Terra and Aqua Moderate-Resolution Imaging
Spectroradiometer (MODIS) scan mirror reflectance is a function
of the angle of incidence (AOI) and was characterized prior
to launch by the instrument vendor. The relative change of
the prelaunch response versus scan angle (RVS) is tracked and
linearly scaled on-orbit using observations at two AOIs of 11.2°
and 50.2° corresponding to the moon view and solar diffuser,
respectively. As the missions continue to operate well beyond
their design life of six years, the assumption of linear scaling
between the two AOIs is known to be inadequate in accurately
characterizing the RVS, particularly at short wavelengths. Con-
sequently, an enhanced approach of supplementing the on-board
measurements with response trends from desert pseudoinvariant
calibration sites (PICS) was formulated in MODIS Collection 6
(C6). An underlying assumption for the continued effectiveness of
this approach is the long-term (multiyear) and short-term (month
to month) stability of the PICS. Previous work has shown that the
deep convective clouds (DCC) can also be used to monitor the on-
orbit RVS performance with less trend uncertainties compared
with desert sites. In this paper, the raw sensor response to the
DCC is used to characterize the on-orbit RVS on a band and
mirror-side basis. These DCC-based RVS results are compared
with those of C6 PICS-based RVS, showing an agreement
within 2% observed in most cases. The pros and cons of using a
DCC-based RVS approach are also discussed in this paper.
Although this reaffirms the efficacy of the C6 PICS-based RVS,
the DCC-based RVS approach presents itself as an effective
alternative for future considerations. Potential applications of this
approach to other instruments, such as Suomi National Polar-
orbiting Partnership, Joint Polar Satellite Systems, and Visible
Infrared Imaging Radiometer Suite, are also discussed.