On-orbit calibration and inter-comparison of Terra and Aqua MODIS surface temperature spectral bands

Two moderate resolution imaging spectroradiometer (MODIS) instruments have been operating on board the NASA EOS Terra and Aqua spacecraft for 7 and 4.5 years, respectively. The MODIS is a cross-track scanning radiometer that collects data in 36 spectral bands with wavelengths from visible (VIS) to long-wave infrared (LWIR). MODIS thermal emissive bands (TEB) on-orbit calibration is performed using an on-board blackbody (BB). Bands 31 and 32, with centre wavelengths at 11 and 12 mu m, are primarily used for surface temperature (ST) retrieval. This paper provides a brief description of MODIS TEB calibration methodology and presents bands 31 and 32 on-orbit performance in terms of their calibration stability and detector noise characterization. It also describes an approach to examine the ST spectral band calibration consistency between two MODIS instruments using similar spectral channels of an advanced very high resolution radiometer (AVHRR) instrument currently operated on board NOAA-16 and NOAA-17. Inter-comparison data sets are carefully selected from near-simultaneous and near-nadir observations made by each pair of MODIS and AVHRR instruments. Results show that ST spectral bands 31 and 32 in both the Terra and Aqua MODIS are performing better than their design requirements, with excellent calibration stability and satisfactory cross-sensor calibration consistency. The on-orbit noise equivalent temperature differences (NEdTs) of all detectors have been continuously below the design specifications of 0.05 K. The calibration coefficients are extremely stable with scan-by-scan variations of less than 0.10%. In addition, calibration differences between two MODIS instruments are less than 0.10 K for both bands 31 and 32.