MODIS on-orbit spatial characterization results using ground measurements

摘要

MODerate resolution Imaging Spectro-radiometer (MODIS), as part of NASA's Earth Observe System (EOS) mission, is widely utilized in diversified scientific research areas. Both Terra and Aqua MODIS observe the earth in sun-synchronous orbit at three nadir spatial resolutions. MODIS has thirty-six bands that are located in four Focal Plane Assembles (FPAs) by wavelength: Visible (VIS), Near-Infrared (NIR), Short-and Middle-wavelength IR (SMIR), and Long wavelength IR (LWIR). MODIS Band-to-Band Registration (BBR) was measured pre-launch at the instrument vendor. Mis-registration exists between bands and FPAs. The spatial characterization could change in storage, at launch, and years on-orbit. In this study, a special ground scene with unique features has been selected as our study area to calculate the spatial registration in both along-scan and along-track for bands 2-7 relative to band 1. The results from the earth scene targets have been compared with on-board calibrator, the Spectro-Radiometric Calibration Assembly (SRCA), with good agreement. The measured differences between the SRCA and our ground scene approach are less than 20m on average for VIS/NIR bands both along-scan and along-track. The differences for SMIR bands are 20m along-scan and 0.1 - 0.18 km for along track. The SMIR FPA crosstalk could be a contributor to the difference. For Aqua MODIS instruments, the spatial deviation is very small between the bands located on the same FPA or between VIS and NIR FPAs but is relatively large between warm (VIS and NIR) and cold (SMIR and LWIR) FPAs. The spatial deviation for MODIS/Terra can be ignorable but not for MODIS/Aqua. The results from this study show that the spatial deviation of Aqua MODIS may impact on the science data when multi-band data from both warm and cold FPAs is combined.