Possible shift of spectral response function of the MODIS 6.8 μm water vapor channel causing a cold bias of 2ndash;3 K

摘要

The calibration of the Moderate-resolution Imaging Spectroradiometer (MODIS)6.8 μm water vapor (WV) channel was assessed by comparing Terra/MODISmeasurements with the WV channel brightness temperatures equivalent toInfrared Atmospheric Sounding Interferometer (IASI) measurements for June 2007 and December 2007. IASI spectral information was transferred to theJapanese Multifunctional Transport Satellite (MTSAT)-1R WV channel and thento the MODIS WV channel. Results indicate that the MODIS WV channel isbiased low by 2–3 K, possibly caused by the shift of the spectral responsefunction by about +11 cm. This finding is particularly importantbecause the bias of −3 K can cause about +30% relative errors in theretrieval of upper tropospheric humidity (UTH) over the tropics. In otherwords, the current MODIS measurements may result in higher UTH values,showing relative errors up to +30%.