Intercomparison of On-Orbit Calibration Consistency Between Terra and Aqua MODIS Reflective Solar Bands Using the Moon

Abstract

Two nearly identical Moderate Resolution Imaging Spectroradiometer (MODIS) sensors, one on the Terra and the other on the Aqua satellite, are currently operating in space, making continuous global observations in 36 spectral bands: 20 reflective solar bands (RSBs) and 16 thermal emissive bands. For MODIS RSB with wavelengths from 0.41 to 2.1 mum, the sensor-specified calibration-accuracy requirements are plusmn2% for reflectance and plusmn5% for radiance products. They are calibrated on-orbit by a solar diffuser (SD) and an SD stability monitor. In addition, lunar observations are scheduled regularly to monitor the RSB radiometric calibration stability. This letter describes an intercomparison method developed for evaluating the calibration consistency between Terra and Aqua MODIS RSBs and calibration differences among detectors in each spectral band. It presents intercomparison results derived from Terra and Aqua MODIS lunar observations made over their overlapped mission operation. This method uses predicted lunar irradiances derived from a lunar model to remove lunar-viewing-geometry differences among different observations made by each sensor. The results, excluding the bands which either have electronic crosstalk or saturate during lunar observations, show that the Terra and Aqua MODIS RSBs have been consistently calibrated to within plusmn1%. For the detectors within any one spectral band, the calibration differences are less than plusmn0.5%. The methodology developed here can be applied to other sensors for intercomparison studies.