Assessment of MODIS collection 6.1 thermal emissive band calibration using hyperspectral IASI observations

Abstract

The Moderate Resolution Imaging Spectroradiometer (MODIS), a key instrument of the NASA Earth Observing System missions, has operated for over 20 years and 18 years onboard the Terra and Aqua satellites, respectively. Sixteen thermal emissive bands (TEBs) are distributed on two cold focal place assemblies with photovoltaic (PV) HgCdTe detectors for bands 20-25 and 27-30 and photoconductive (PC) HgCdTe detectors for bands 31-36. This paper evaluates the performance of the latest MODIS Collection 6.1 (C6.1) Level-1B products with a focus on the relative differences between the Terra and Aqua MODIS TEBs. The Infrared Atmospheric Sounding Interferometer (IASI) onboard the Metop-A satellite serves as a reference. Observations obtained from the simultaneous nadir overpass between the Terra (or Aqua) and Metop-A satellites are used to track the brightness temperature differences between MODIS and IASI. The assessment is based on the temperature differences as a function of scene temperature and their trends in comparison with IASI from years 2007 to 2020. The results confirm that the calibration of Terra MODIS bands 27-30 significantly improved in C6.1 after implementing the electronic crosstalk correction. In spite of these corrections, Terra MODIS shows a larger drift in PV LWIR bands 27-30 than Aqua MODIS when compared to IASI.A sensitivity study is performed, where the center wavelength of the MODIS relative spectral response is shifted, and as a result some of these bands show a significant improvement in scene temperature dependency and their consistency with IASI measurements.