Performance of the Terra MODIS on-board blackbody

The Moderate Resolution Imaging Spectroradiometer (MODIS) has 36 spectral bands covering wavelengths from 0.41 to 14.4_m. It is a cross-track scanning radiometer that uses a two-sided paddle-wheel scan mirror to make observations over a wide field-of-view (FOV). Each scan of 1.478 seconds, it produces a swath of 10km along-track (at nadir) by 2330km along-scan. Bands 1-19 and 26 are the reflective solar bands (RSB) and bands 20-25 and 27-36 are the thermal emissive bands (TEB). There are a total of 160 detectors (10 detectors per band) for the thermal emissive bands that are calibrated on-orbit by a blackbody (BB) on a scan-by-scan basis. The spectral radiance of each individual TEB detector is calculated every scan from the BB source temperature. The temperature of the BB is measured by a set of 12 thermistors. On-orbit performance of the BB, such as its temperature stability and uncertainty, directly impacts the TEB calibration and data product quality. Excluding a few spacecraft and instrument related anomalies or safe hold events, the Terra MODIS (launched in December 1999) BB has operated continuously on-orbit for more than five years. Using its on-orbit calibration data, this paper examines the Terra MODIS BB performance and its impact on the TEB calibration uncertainty. The results show that the Terra MODIS BB has been performing extremely well in terms of its reliability and stability. Under the same operating configuration, the average BB temperature drift per year (long-term stability) is less than 0.005K. The scan-to-scan temperature variation (short-term stability) is within ±0.03K. Also illustrated in this paper are examples of the TEB detectors' responses to the on-board BB and the detectors' noise characterization results at different BB temperatures.