Xiong, XX, Wenny, BN, Wu, AS, Barnes, WL (2009). MODIS Onboard Blackbody Function and Performance. IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING, 47(12), 4210-4222.
Two Moderate Resolution Imaging Spectroradiometer (MODIS) instruments are currently in orbit, making continuous global observations in visible to long-wave infrared wavelengths. Compared to heritage sensors, MODIS was built with an advanced set of onboard calibrators, providing sensor radiometric, spectral, and spatial calibration and characterization during on-orbit operation. For the thermal emissive bands (TEB) with wavelengths from 3.7 to 14.4 mu m, a v-grooved blackbody (BB) is used as the primary calibration source. The BB temperature is accurately measured each scan (1.47 s) using a set of 12 temperature sensors traceable to the National Institute of Standards and Technology (NIST) temperature standards. The onboard BB is nominally operated at a fixed temperature, 290 K for Terra MODIS and 285 K for Aqua MODIS, to compute the TEB linear calibration coefficients. Periodically, its temperature is varied from 270 K (instrument ambient) to 315 K in order to evaluate and update the nonlinear calibration coefficients. This paper describes MODIS onboard BB functions with emphasis on on-orbit operation and performance. It examines the BB temperature uncertainties under different operational conditions and their impact on TEB calibration and data product quality. The temperature uniformity of the BB is also evaluated using TEB detector responses at different operating temperatures. On-orbit results demonstrate excellent short-term and long-term stability for both the Terra and Aqua MODIS onboard BB. The on-orbit BB temperature uncertainty is estimated to be 10 mK for Terra MODIS at 290 K and 5 mK for Aqua MODIS at 285 K, thus meeting the TEB design specifications. In addition, there has been no measurable BB temperature drift over the entire mission of both Terra and Aqua MODIS.