Preliminary estimate of calibration of the moderate resolution imaging spectroradiometer thermal infrared data using Lake Titicaca

The absolute radiometric accuracy of Moderate Resolution Imaging Spectroradiometer (MODIS) thermal infrared (TIR) data was evaluated with in situ data collected in a vicarious calibration field campaign conducted in Lake Titicaca, Bolivia during May 26 and June 17, 2000. The comparison between MODIS TIR data produced by the version 2.5.4 Level-1B code and the band radiances calculated with atmospheric radiative transfer code MODTRAN4.0 based on lake surface kinetic temperatures measured by five IR radiometers deployed in the high-elevation Lake Titicaca and the atmospheric temperature and water vapor profiles measured by radiosondes launched on the lake shore on June, 15 2000, a calm clear-sky day, shows good agreements in bands 31 and 32 (within an accuracy of 0.4%) in the daytime overpass case. Sensitivity analysis indicates that the changes on the measured atmospheric temperature and water vapor profiles result in negligible or small effects on the calculated radiances in the atmospheric window bands (bands 20–23, 29, and 31–32). Therefore, comparisons for these bands were made for cases when lake surface temperature measurements were available but no radiosonde data were available and in subareas of 10×16 pixels where there was no in situ measurement but MODIS brightness temperatures in band 31 vary within ±0.15 K by using the validated band 31 to determine lake surface temperatures through the MODTRAN4.0 code. Comparisons and error analysis show that the specified absolute radiometric accuracies are reached or nearly reached in MODIS bands 21, 29, and 31–33 and that there is a calibration bias of 2–3% in bands 20, 22, and 23. The error analysis also shows that the radiosondes cannot provide accurate atmospheric temperature and water vapor profiles to estimate the calibration accuracies in the atmospheric sounding bands (bands 24–25, 27–28, and 34–36) at the specified 1% level and that the calibration accuracy in the ozone band 30 cannot be estimated without in situ measurements of ozone.