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 b Sciences and Exploration Directorate, NASA/GSFC, Greenbelt, MD 20707, USA (SPIE Defense, Security, and Sensing, Baltimore, MD, USA, 05/01/2013)

 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 Outlines

Introduction IASI Pixel MODIS Pixel Onboard SatelliteSpectral Channels Spectral Range Nadir Spatial Res. Sample # in scan direction Scan Angle Range MODIS Terra:13+yrs Aqua:10+yrs band 1-19, 26 (RSB) 0.4~2.3μm 250m 500m 1km 1354 frames  55  band 20-25, (TEB) 3.6~14.4μm1km IASIMetOp-A:6+yrs8461 spectral samples3.62 ~15.5 μm12km 30 2x2 IFOV ±48  20’ IFOV: instantaneous field of view; RSB: reflectance solar band; TEB: thermal emissive band MODIS: Moderate Resolution Imaging Spectroradiometer IASI : Infrared Atmospheric Sounding Interferometer Spectral Channels Spatial Resolution

Introduction IASI Pixel MODIS Pixel Spectral Channels Spatial Resolution  Terra/Aqua MODIS intercomparison is conducted using IASI 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

 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/Aqua MODIS differences are estimated in brightness temperature (BT) for all thermal emissive bands (TEB), except B21 (low gain band for fire detection) Introduction

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 Methodology

Data Processing  IASI simulated MODIS radiance Methodology λ IASI(low), λ IASI(up) : adjacent wavelengths in IASI spectral samples lower and higher than λ. [λ 1,λ 2 ]: range of Relative Spectral Response (RSR) wavelength rad simulated(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

Data Collected Results

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

Results MODIS / IASI SNO Locations Terra Aqua

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

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

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

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

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

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

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

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

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

Results Average Differences between MODIS and IASI Measurements

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

Results Long-term Comparison Time Series

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