Long‐term assessment of Aqua MODIS radiance observation using comparisons with AIRS and IASI

Abstract

AbstractThis paper presents a detailed comparison between Atmospheric Infrared Sounder (AIRS) and Moderate Resolution Imaging Spectroradiometer (MODIS) measurements over the period 2003–2013 and also between MODIS and Infrared Atmospheric Sounding Interferometer (IASI) for the years 2007–2014. For this study AIRS and IASI high spectral resolution data are degraded to MODIS broadband spectral resolution and MODIS fields of view are averaged within the AIRS and IASI footprints. Using spatially uniform scenes, the brightness temperature differences (ΔBT) between MODIS and AIRS are analyzed as a function of scene temperature, scan angle, and solar zenith angle. In general, the measurements of the two sensors are in good agreement (ΔBT less than ±0.2 K) with little or no dependence on the scene temperature. A small dependence is found for the scan angle, where ΔBT varies off nadir up to about ±0.4 K; dependence on the solar zenith angle is also observed, with ΔBT varying up to ±0.5 K. Finally, the variation of ΔBT over time is stable with BT trending less than 0.02 K/yr, with exception of ΔBT for MODIS bands 33 and 35 in the 2011–2013 timeframe. This behavior, which is also identified in MODIS/IASI comparisons, correlates to adjustments in that timeframe of the MODIS nonlinear calibration coefficients.