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Yonghong Li a , Aisheng Wu a , Xiaoxiong Xiong b

Evaluating Calibration of MODIS Thermal Emissive Bands Using Infrared Atmospheric Sounding Interferometer Measurements. Yonghong Li a , Aisheng Wu a , Xiaoxiong Xiong b a Sigma Space Corporation, 4801 Forbes Blvd, Lanham, MD 20706, USA

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Yonghong Li a , Aisheng Wu a , Xiaoxiong Xiong b

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  1. Evaluating Calibration of MODIS Thermal Emissive Bands Using Infrared Atmospheric Sounding Interferometer Measurements Yonghong Lia, Aisheng Wua, Xiaoxiong Xiongb • aSigma Space Corporation, 4801 Forbes Blvd, Lanham, MD 20706, USA • bSciences and Exploration Directorate, NASA/GSFC, Greenbelt, MD 20707, USA (SPIE Defense, Security, and Sensing, Baltimore, MD, USA, 05/01/2013)

  2. Outlines • Introduction • Methodology • Simultaneous Nadir Overpasses (SNOs) • Data processing • Results • Data collected • Terra/Aqua MODIS vs. IASI comparison scatter plots • Terra/Aqua MODIS C5 vs. C6 inter-comparison • Long-term comparison time series • Summary

  3. Introduction MODIS: Moderate Resolution Imaging Spectroradiometer IASI : Infrared Atmospheric Sounding Interferometer IFOV: instantaneous field of view; RSB: reflectance solar band; TEB: thermal emissive band Spectral Channels Spatial Resolution IASI Pixel MODIS Pixel

  4. Introduction • Terra/AquaMODIS intercomparison is conducted usingIASI measurements as a transfer reference • IASI hyperspectral measurements are converted to MODIS spectral band radiances • Measurements from multiple MODIS pixels geo-collocated within an IASI instantaneous fields of view (IFOV) are aggregated Spectral Channels Spatial Resolution IASI Pixel MODIS Pixel

  5. Introduction • MODIS inter-comparison is focused on L1B products • current calibration version Collection 5 (C5) has produced L1B products since 2005 • recently released Collection 6 (C6) contains a major adjustment in calibration coefficient estimate to handle known issues with the aging MODIS sensors • Terra/AquaMODIS differences are estimated in brightness temperature (BT) for all thermal emissive bands (TEB), except B21 (low gain band for fire detection)

  6. Methodology Simultaneous Nadir Overpasses (SNOs) • SNO time difference was limited to within 30 seconds • IASI nadir includes two pairs of IFOVs at scan center (~ ±1.6) • MODIS nadir includes ±10 around nadir point • Aqua / IASI SNOs: • near ±73.9 latitude • ~ 20 IASI IFOVs in each IASI/Aqua SNO event • Terra / IASI SNOs: • near ±80.9 latitude • ~ 77 IASI IFOVs in each IASI/Terra SNO event • Two SNO events are chosen in each month from May 2007 ~ Dec. 2012

  7. Methodology Data Processing • IASI simulated MODIS radiance λIASI(low), λIASI(up): adjacent wavelengths in IASI spectral samples lower and higher than λ. [λ1,λ2]: range of Relative Spectral Response (RSR) wavelength radsimulated(MODIS): band average. • Multiple MODIS pixel measurements in an IASI IFOV are aggregated • MODIS 1-km pixels are collocated with an IASI 12-km IFOV • A radius of 6-km is used to represent one IASI IFOV • Typically >100 MODIS pixels are collocated within one IASI IFOV • Only IFOVs with >70 MODIS pixels are considered in SNO data collection MODIS Pixel IASI Pixel

  8. Results Data Collected

  9. Results Correlations between IASI and MODIS on Band Average Terra C6 Terra vs. IASI correlations are larger than 0.99 for B27-36. For other bands, the correlations vary in the range of [0.93, 0.98] except B24 with correlation of 0.89. Aqua vs. IASI correlations are larger than 0.99 for all TEB bands. The correlations are very close between C6 and C5 data.

  10. Results MODIS / IASI SNO Locations Terra Aqua

  11. Results MODIS / IASI SNO Match Pixels Aqua C6 Sept.02, 2012 Terra C6 Sept.01, 2012 IASI Pixel MODIS Pixels

  12. Results MODIS Band Average Intercomparison Scatter Plots C5 C6 + Terra ◇ Aqua

  13. Results MODIS Band Average Intercomparison Scatter Plots C5 C6 + Terra ◇ Aqua

  14. Results MODIS Band Average Intercomparison Scatter Plots C5 C6 + Terra ◇ Aqua

  15. Results MODIS Band Average Intercomparison Scatter Plots C5 C6 + Terra ◇ Aqua

  16. Results MODIS Band Average Intercomparison Scatter Plots C5 C6 + Terra ◇ Aqua

  17. Results MODIS Band Average Intercomparison Scatter Plots C5 C6 + Terra ◇ Aqua

  18. Results MODIS Band Average Intercomparison Scatter Plots C5 C6 + Terra ◇ Aqua

  19. Results MODIS Band Average Intercomparison Scatter Plots C5 C6 + Terra ◇ Aqua

  20. Results Average Differences between MODIS and IASI Measurements

  21. Results Long-term Comparison Time Series Terra C6 MODIS-IASI comparison time series for band 31

  22. Results Long-term Comparison Time Series

  23. Summary • IASI vs. MODIS SNO data are highly correlated (~0.99) indicating a good quality of comparison between IASI and MODIS • In comparison with MODIS C5, current C6 significantly reduces the differences between MODIS and IASI measurements as well as differences between Terra /Aqua MODIS in bands 20,22-25,27-32 • Long-term comparison time series show MODIS calibration consistency over time

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