SPIE Journal Paper | 15 April 2022
KEYWORDS: MODIS, Reflectivity, Calibration, Near infrared, Cameras, Domes, Sensors, Space operations, Polarization, Spatial resolution
As a part of NASA’s Earth Observing System (EOS), the Terra spacecraft was launched on December 18, 1999, with the goal of understanding the changes of the Earth, by examining the Earth’s hydrological, geophysical, and climatic processes. The Moderate-resolution Imaging Spectroradiometer (MODIS) and Multi-angle Imaging Spectroradiometer (MISR) instruments on the Terra platform, combined with their continuous operation, broad spectral coverage, and different spatial resolutions, have played an important role to achieve the goals of the EOS. Over two decades of successful operations, these multispectral imaging instruments have benefited a variety of scientific applications. Being on the same platform, the two sensors complement each other in terms of spatial coverage (and target viewing geometry) and facilitate synergistic applications using multispectral data. A consistent radiometric calibration between these sensors is a prerequisite for creating high-quality science products from their observations. Both instruments underwent intensive prelaunch characterization and their on-orbit calibrations are monitored using their onboard calibrators. We perform a calibration inter-comparison of the spectrally matching bands of the two instruments using vicarious techniques. These techniques include multiyear simultaneous views of the North African desert, North Atlantic Ocean, and Dome Concordia; therefore, covering different reflectance regimes. Moreover, the near-simultaneous top-of-atmosphere (TOA) reflectance measurements from Railroad Valley (RRV), as provided by the radiometric calibration network (RadCalNet) (converted to TOA), are also included, which is used as a calibration reference to compare the on-orbit observations between MODIS and MISR. Simultaneous overpasses from desert, ocean, Dome C, and RadCalNet over RRV reveal that the agreement between the four spectrally matching bands is within 3% for the time-period between 2014 and 2020. Furthermore, some long-term drifts are observed in the TOA reflectance time-series from MISR for the red and NIR bands that are expected to be corrected in a future calibration reprocess.
