Evaluating the impact of cold focal plane temperature on Aqua MODIS thermal emissive band calibration

Abstract

Aqua MODIS, the second MODIS instrument of the NASA Earth Observation System, has operated for over thirteen years since launch in 2002. MODIS has sixteen thermal emissive bands (TEB) located on two separate cold focal plane assemblies (CFPA). The TEB are calibrated using onboard blackbody and space view observations. MODIS CFPA temperature is controlled by a radiative cooler and heaters in order to maintain detector gain stability. Beginning in 2006, the CFPA temperature gradually varies from its designed operating temperature with increasing orbital and seasonal fluctuations, with the largest observed impacts on the TEB photoconductive (PC) bands. In Aqua Collection 6 (C6), a correction to the detector gain due to the CFPA temperature variation is applied for data after mid-2012. This paper evaluates the impact of the CFPA temperature variation on the TEB PC band calibration through comparisons with simultaneous nadir overpasses (SNO) measurements from the Infrared Atmospheric Sounding Interferometer (IASI) and Atmospheric Infrared Sounder (AIRS). Our analysis shows that the current L1B product from mid-2011 to mid-2012 is affected by the CFPA temperature fluctuation. The MODIS-IASI comparison results show that no drift is observed in PC bands over the CFPA temperature variation range. Similarly, in the MODIS-AIRS comparison, bands 31-34 show nearly no trend over the range of CFPA temperature while a slight drift in bands 35-36 are seen from the comparison results.