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On-orbit Performance and Calibration Improvements for the Reflective Solar Bands of Terra and Aqua MODIS

TitleOn-orbit Performance and Calibration Improvements for the Reflective Solar Bands of Terra and Aqua MODIS
Publication TypePresentation
Year of Publication2016
AuthorsAngal, A., X. Xiong, A. Wu, H. Chen, X. Geng, D. Link, Y. Li, A. Wald, and J. Brinkmann
ProceedingsProc. of SPIE Earth Observing Missions and Sensors: Development, Implementation, and Characterization IV
MCST ConferenceProc. of SPIE Earth Observing Missions and Sensors: Development, Implementation, and Characterization IV
Volume9881
Abstract

Moderate Resolution Imaging Spectroradiometer (MODIS) is the keystone instrument for NASA’s EOS Terra and
Aqua missions, designed to extend and improve heritage sensor measurements and data records of the land, oceans
and atmosphere. The reflective solar bands (RSB) of MODIS covering wavelengths from 0.41 μm to 2.2 μm, are
calibrated on-orbit using a solar diffuser (SD), with its on-orbit bi-directional reflectance factor (BRF) changes
tracked using a solar diffuser stability monitor (SDSM). MODIS is a scanning radiometer using a two-sided paddle-
wheel mirror to collect earth view (EV) data over a range of ±550 off instrument nadir. In addition to the solar
calibration provided by the SD and SDSM system, lunar observations at nearly constant phase angles are regularly
scheduled to monitor the RSB calibration stability. For both Terra and Aqua MODIS, the SD and lunar observations
are used together to track the on-orbit changes of RSB response versus scan angle (RVS) as the SD and SV port are
viewed at different angles of incidence (AOI) on the scan mirror. The MODIS Level 1B (L1B) Collection 6 (C6)
algorithm incorporated several enhancements over its predecessor Collection 5 (C5) algorithm. A notable
improvement was the use of the earth-view (EV) response trends from pseudo-invariant desert targets to characterize
the on-orbit RVS for select RSB (Terra bands 1-4, 8, 9 and Aqua bands 8, 9) and the time, AOI, and wavelength-
dependent uncertainty. The MODIS Characterization Support Team (MCST) has been maintaining and enhancing
the C6 algorithm since its first update in November, 2011 for Aqua MODIS, and February, 2012 for Terra MODIS.
Several calibration improvements have been incorporated that include extending the EV-based RVS approach to
other RSB, additional correction for SD degradation at SWIR wavelengths, and alternative approaches for on-orbit
RVS characterization. In addition to the on-orbit performance of the MODIS RSB, this paper also discusses in detail
the recent calibration improvements implemented in the MODIS L1B C6.

DOI10.1117/12.2223912