Calibration improvements in the detector-to-detector differences for the MODIS ocean color bands

Abstract

The Moderate Resolution Imaging Spectroradiometer (MODIS), a major instrument within NASA’s Earth Observation System missions, has operated for over 16 and 14 years onboard the Terra and Aqua satellites, respectively. Its reflective solar bands (RSB) covering a spectral range from 0.4 to 2.1 μm are primarily calibrated using the on-board solar diffuser (SD), with its on-orbit degradation monitored using the Solar Diffuser Stability Monitor. RSB calibrations are supplemented by near-monthly lunar measurements acquired from the instrument’s space-view port. Nine bands (bands 8-16) in the visible to near infrared spectral range from 0.412 to 0.866 μm are primarily used for ocean color observations. During a recent reprocessing of ocean color products, performed by the NASA’s Ocean Biology Processing Group, detector-to-detector differences of up to 1.5% were observed in bands 13-16 of Terra MODIS. This paper provides an overview of the current approach to characterize the MODIS detector-to-detector differences. An alternative methodology was developed to mitigate the observed impacts for bands 13-16. The results indicated an improvement in the detector residuals and in turn are expected to improve the MODIS ocean color products. This paper also discusses the limitations, subsequent enhancements, and the improvements planned for future MODIS calibration collections.